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SMITHSONIAN DEPOSIT. 



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CHEMISTEY 

INORGANIC AND ORGANIC 



>p*~ 



CHEMISTRY 



INORGANIC AND ORGANIC 



WITH EXPERIMENTS 



BY 



CHARLES LOUDON BLOXAM, 

u 

rROFESSOR OF CHEMISTRY IN KINO'S COLLEGE ,10KDOSj IN THE ROYAL VI LIT ART AC1DIMV 
WOOLWICH AND IV THE DEPARTMENT OF ARTILLERY STUDIES , WOOL WICU. 




SECOND EDITION, 



PHILADELPHIA: 
LINDSAY & BLAKISTON, 



1872. 



«$u 



?1 



EXTRACTS 



FROM THE 



PREFACE TO THE FIEST EDITION 



This work is designed to give a clear and simple description of 
the elements and their principal compounds, and of the chemical 
principles involved in some of the most important branches of 
manufacture. Keeping this in view, I have employed as few 
technical terms as possible, especially at the commencement, so 
that the student may glide into Chemistry without having first 
to toil through a difficult chapter on the terminology of the 
science, which he can never appreciate until he has become 
acquainted with the examples which serve to illustrate its appli- 
cation. 

Convinced, by experience, of the great assistance afforded to 
the learner by referring him to a simple illustrative experiment, 
I have introduced, generally in smaller type, a description, and 
in most cases a wood-engraving, of the experiments which I 
have found most useful in illustrating lectures, hoping that these 
may prove of service in fixing the attention of the student, and 
may assist those who are desirous of performing such experiments 
for their own instruction, or for that of a class. 

In general, English weights and measures, and Fahrenheit ther- 
mometric degrees, have been employed, as conveying more clearly 
to the beginner the absolute values expressed, since the mental 
effort of converting what must still be called the Continental 
systems, slight though it be, might have the effect of diverting 
the attention of the reader from the chemical question under 
consideration. The various calculations have been conducted in 
the simplest arithmetical form, because the more compendious 



VI PREFACE. 

algebraical expressions are not so generally intelligible, and when 
the principle is once understood, a general algebraical formula for 
the calculation is easily constructed by the learner. 

The special attention devoted to Metallurgy and some other 
branches of Applied Chemistry, will render the work useful to 
those who are being educated for employment in manufacture. 

The military student will find more than the usual space allotted 
to the chemistry of the various substances employed in warlike 
stores. 

C. L. B. 



PREFACE TO THE SECOND EDITION, 



During the five years which have elapsed since the publication 
of the First Edition of this work, the adoption of the atomic system 
of notation has become so general among English chemists that 
I have felt obliged to employ it in the present edition. This 
change has rendered it necessary to commence the study of the 
non-metallic elements with Hydrogen instead of Oxygen, a course 
attended with some disadvantage to beginners, because Hydrogen 
is prepared and studied by processes which are strictly technical, 
whereas Oxygen is known in a free state in the atmosphere, where 
we constantly witness its chemical action upon other bodies. 
Moreover, the circumstance that the science of chemistry origin- 
ated in the careful study of the phenomena of combustion towards 
the end of the last century, appears to me greatly in favour of our 
commencing a course of elementary chemistry from that point. 
Since, however, Hydrogen is the chemical unit of the atomic 
system, whilst Oxygen is a diatomic element, I have found it 
absolutely necessary to assign to this latter the second place. 
Indeed, to teach the atomic system in its integrity, it would be 
necessary to postpone the study of Oxygen until all the monatomic 
elements had been disposed of, and thus to defer, till a late period, 
the consideration of the processes of combustion which awaken 
the interest of even the least observant student. 

Although I thoroughly appreciate the beauty and harmony of 
the atomic system, and acknowledge the immense assistance which 
it has afforded in research, I contemplate with regret its almost 



Vlll PREFACE. 

universal adoption by chemical teachers in this country, since it 
involves the necessity of propounding the difficult hypothesis of 
the finite divisibility of matter at the commencement of a study 
which has been recommended to the student as strictly experi- 
mental, and as affording a mental relief from the abstractions of 
mathematics. Even if it be alleged that it is not necessary to 
mention atoms to beginners, but that the teacher .may confine 
himself, as is now sometimes the case, to combining proportions, 
the combining weight of hydrogen in water must be represented 
as 2 ; a perplexing, and at this stage totally unnecessary inquiry 
being suggested to the mind of the pupil, why it is set down as 1 
in the lists of combining weights. 

The numerous failures in Chemistry at the examinations now so 
much in vogue, appear to indicate the difficulty experienced by 
the immature minds of the young in laying hold of the ideas of 
atomicity and quantivalence which pervade many of the questions, 
whereas the mutual relations between the elements and their com- 
pounds, which are easily impressed on the mind by experiment, 
and involve as much Chemistry as the young student can grasp, 
are treated as of subordinate importance. 

The tendency to regard Chemistry as a modified Algebra has 
become so great since the general introduction of the atomic 
system, that it is not uncommon for teachers in schools to prepare 
the pupils for examination in Chemistry, who have themselves 
never had the opportunity of learning how to conduct the simplest 
chemical operation. 

To acquire a knowledge of the rudiments of Chemistry by per- 
sonal observation, has, without doubt, a very beneficial effect ; but 
to get tip a number of formulas and equations, with the sole object 
of gaining a certain number of marks at examination, altogether 
defeats the object with which Chemistry should be introduced into 
a system of liberal education. 

In this edition I have endeavoured to preserve, as far as possible, 
the simple and experimental character of the work, and at the 
same time to employ formulae in harmony with those now gene- 
rally used. The nomenclature has undergone very little change, 
since there is by no means a general agreement upon this subject ; 
and I deem it of the greatest importance that tie names by which 



PREFACE. IX 

chemical compounds are known in common life should be kept 
before the student in a chemical treatise. 

The attention of the student is called to the Table of Contents, 
which has been drawn up to serve the purpose of an abstract, by 
which he may examine himself upon each paragraph of the book. 
The Index is also a dictionary of the most important formulas, in 
which either the name of a compound may be referred to, in order 
to find its formula, or the formula may be sought when it is 
desired to ascertain the compound to which it belongs. 

C. L. B. 

King's College, London, 
July 1872. 



*j* In the following pages, the smaller type contains not only 
the descriptions of experiments, but all such matter as would be 
of less importance to a student desiring only a general knowledge 
of the subject without going into details.' 

A Table of Atomic Weights w T ill be found at page 628. 



TABLE OF CONTENTS. 



Paragraph 

Introduction. — Definitions, . . . . . 1 

Enumeration and classification of elements, with their symbols, . 2 

Classification of compounds into organic and inorganic, . . 3 

Chemistry of the Non-metallic Elements and their Compounds. 
Water. — Analysis of water by the galvanic battery ; construction of 

Grove's battery, ....... 4 

Electrolysis ; electro-positive and electro-negative elements, . . 5 

Relative volumes of hydrogen and oxygen in water ; difference in ap- 
plication of electricity according to quantity and intensity, . 6 
Decomposition of steam into detonating gas by heat and electric 

sparks, ........ 7 

Law of definite proportions ; atomic theory ; atomic heat, . . 8 

Disengagement of hydrogen from water by metals ; definition of an 
alkali ; definition of chemical equivalent of a metal ; action of 
potassium and sodium on water; classification of metals according 
to their action upon water, ..... 9 

Hydrogen. — Preparation of hydrogen by action of red-hot iron upon 

steam ; by action of zinc or iron upon diluted sulphuric acid, . 1 

Physical properties of hydrogen ; its value as a theoretical unit of 

volume ; illustrations of its extreme lightness, . . .11-12 

Diffusibility of gases defined and illustrated"; separation of hydrogen 

and oxygen by atmolysis ; law of the velocities of diffusion, . 13 

Chemical properties of hydrogen ; character of its flame, . . 14 

Explosive mixtures of hydrogen with air and oxygen, . . 15 

Oxygen. — Its occurrence in nature, . . . . .16 

Physical properties of oxygen. Specific gravity of gases defined, . 17 
Chemical properties of oxygen. Combustion, . . . 18 

Relations of oxygen to phosphorus ; effects of heat and minute divi- 
sion upon chemical attraction ; nature of acids, . . 19 
Relations of oxygen to sulphur, . ... .20 

Relations of oxygen to carbon, . . . • .21 

Etymology of oxygen. Definition of an acid, . . .22 

Relations of oxygen to the metals ; sodium and oxygen, . . 23 

Relations of oxygen to zinc ; definition of base, salt, salt-radical, . 24 
Relations of oxygen to iron ; naming of oxides to indicate their com- 

K position ; definition of a metal, . . . ■ .25 

Indifferent oxides, . . . . . . .26 

Preparation of oxygen from atmospheric air, . . .27 

„ „ binoxide of manganese, . . .28 



Xll CONTENTS. 

Paragraph 
Preparation of oxygen from chlorate of potash ; calculation of the 

weight of a given volume of gas, ... .29 

Water. — Synthesis of water from its elements, . . . .30 

Explosion of hydrogen and oxygen in the eudiometer, . . . 31 

Eudiometric analysis of air, ...... 32 

Synthesis of vapour of water ; atoms and molecules, . . .33 

Synthesis of water by weight, ...... 34 

Reciprocal character of combustion, . . ,. .. .35 

Oxyhydrogen blow-pipe, ...... 36 

Chemical relations of hydrogen ; Hydrogenium ; occlusion of hydrogen 

by palladium, . . . . . . .37 

Chemical relations of ivater to other substances ; hydrates ; nature of 
simple solution ; crystallisation from water ; super-saturated 
solutions, ........ 38 

Efflorescence ; water of crystallisation and water of constitution of 

salts ; deliquescence, ...... 39 

Hydrated bases ; unitary and dualistic views of alkaline hydrates, 40 

Hydrated acids ; unitary and dualistic views of hydrated sulphuric 

acid, . . . . . • . .41 

Water from various natural sources ; air dissolved in water, . . 42 

Saline components of natural waters ; hardness ; boiler incrustations ; 

petrifying springs; stalactites; processes for softening waters; 

temporary and permanent hardness ; organic matter in waters, . 43 

Action of water upon leaden cisterns and pipes. Mineral waters, . 44 

Sea-water, . . . . . . . .45 

Purification of water by distillation ; the still and worm ; Liebig's 

condenser, . . . . . .46 

Physical properties of water ; specific gravity of liquids and solids 

defined ; definition of boiling-point, . . . .47 

Peroxide of hydrogen : its preparation and properties ; decomposi- 
tion by contact ; positive and negative oxygen, . . 48 
Ozone : its constitution and production ; ozonic ether ; Dr Day's test 

for blood, . . . . . .49 

Atmospheric air. — Its composition ; rough demonstration of the pro- 
portions of oxygen and nitrogen by phosphorus ; exact analysis of 
air by copper, ....... 50 

Air a mixture, not a chemical compound ; functions of the nitrogen 
in air ; uniform composition of the atmosphere maintained by 
diffusion; dialysis of air ; Sprengel's air-pump, . . 51 

Carbon. — Its natural varieties ; demonstration of the nature of diamond ; 

exact synthesis of carbonic acid ; graphite; its useful applications, . 52 
Artificial varieties of carbon ; lamp-black, wood-charcoal ; destructive 
distillation defined ; charcoal-burning ; decolorisation and deodor- 
isation by charcoal ; animal charcoal ; calorific value of carbon, . 53 
Coal. — Chemistry of its formation ; composition and special uses of lig- 
nite, bituminous coal and anthracite, . . . .54 

Oxides of carbon ; their composition by weight, . . 55 

Carbonic acid. — Sources of atmospheric carbonic acid ; respiration ; fer- 
mentation ; decomposition of carbonic acid by plants, . . 56 
Occurrence of carbonic acid in the mineral kingdom ; preparation of 

carbonic acid, . . . . . .57 



CONTENTS. xill 

Paragraph 
Properties of carbonic acid ; illustrations of its high specific gravity 
and power of extinguishing flame ; limit to combustion of a taper 
in confined air ; limit to respiration of animals in confined air; 
noxious effects of carbonic acid ; principles of ventilation ; solu- 
bility of carbonic acid in water ; sparkling drinks ; importance 
of dissolved carbonic acid to plants, . . . .58 

Liquefaction of carbonic acid in glass tubes and in iron cylinders ; 
continuity of the gaseous and liquid states of matter ; experi- 
ments with solid carbonic acid, ..... 59 

Separation of carbonic acid from other gases, . . .60 

Ultimate analysis of organic substances ; calculation of formula? exem- 
plified ; empirical and rational formulae, . . . .61 

Salts formed by carbonic acid. Table of the commonest carbonates, 

with their common names, additive and substitutive formulae, . 62 
Analytical proof of the composition of carbonic acid, . . 63 

Carbonic oxide. — Its formation in fires and furnaces ; its poisonous 

character, . . . . . . .64 

Formation of carbonic oxide by passing steam over red-hot carbon ; 

its useful applications, . . x . . . .65 

Carbonic oxide compared with carbonic acid, . . .66 

Preparation of carbonic oxide ; from oxalic acid ; from ferrocyanide 

of potassium, . . . . . . .67 

Reduction of metallic oxides by carbonic oxide ; preparation of pyro- 

phoric iron, . ... . . . .68 

Composition by volume of carbonic oxide and carbonic acid, . 60 

Atomic weight of carbon, ...... 70 

Compounds of carbon and hydrogen ; formula' of acetylene, marsh-gas, 

and olefiant-gas, . . . . . . .71 

Acetylene. — Its production by direct synthesis ; its preparation in quantity 
by the imperfect combustion of coal-gas ; new radicals derived from 
acetylene ; cupros-acetyle, argent- acetyle ; fulminating oxide of 
argent-acetyle ; remarkable properties of acetylene ; formation of 
styrole by action of heat upon acetylene f synthesis of prussic acid 
with acetylene and nitrogen, . . . . .72 

Olefiant gas. — Its preparation and properties ; formation of Dutch liquid ; 

production of acetylene from olefiant gas by the spark-discharge, . 73 
2Iarsh-gas. — Its occurrence in nature ; fire-damp ; preparation and pro- 
perties of marsh-gas; chemistry of explosions in coal-mines; safety- 
lamps, . . . . . . . .74 

Structure of flame ; cause of luminosity in ordinary flames ; experiments 
illustrating the structure of flame ; influence of the supply of air 
upon the character of flames ; smokeless gas-burners ; effect of 
atmospheric pressure upon the luminosity of flames ; composition 
of illuminating fuels, . . . . . .75 

The bloivpipe flame. — Functions of its different parts ; reduction of metals 

by the blowpipe, on charcoal ; hot-blast blowpipe, . . 76 

Eudiometric analysis of marsh-gas, . . . . .77 

Coal-gas. — Products of the distillation of coal, . . .78 

Silicon. — Its occurrence as silica in nature ; conversion of silica into a 
soluble form ; preparation of pure silica by dialysis ; crystallised and 
arnorphorous silica, ....... 79 



XIV 



CONTENTS. 



Apparatus for effecting fusions in the laboratory, 

Silicates ; bibasic character of silicic acid, .... 

Preparation and properties of silicon ; amorphous, graphitoid, and 
adamantine silicon ; comparison of silicon with carbon ; hydride of 
silicon ; atomic weight of silicon, .... 

Boron. — Boracic acid; its extraction from the soffioni; properties of 
boracic acid ; borates, ..... 

Extraction of boron from boracic acid ; amorphous and diamond boron 
Eeview of carbon, boron,- and silicon, ... 
Nitrogen. — Its occurrence in Nature and preparation from air ; inert 
character of the element, and activity of its compounds, 
Ammonia. — An important medium of circulation for nitrogen ; extrac 
tion from the ammoniacal liquor of the gas-works ; sublimation 
preparation of ammonia gas ; solution of ammonia ; mode of ascer- 
taining its strength ; liquefaction of ammonia ; Carry's refrigerator 
combination of ammonia with acids ; the ammonium-theory ; for- 
mation of ammonium-amalgam, . 
Atomic weight and volume of nitrogen, 
Process for ascertaining the proportion of nitrogen in an organic sub 

stance ; calculation of the formula of urea, 
Formation of ammonia in the rusting of iron ; nascent state of elements 
Production of nitrous and nitric acids from ammonia ; nitrification 

formation of nitrates in nature, . 
Compounds of nitrogen and oxygen, . . . 

Nitric acid. — Preparation in the laboratory and on the large scale ; pro- 
perties of nitric acid ; its action upon metals and organic substances, 
Oxidising effects of nitrates. Combining weight and formula of nitric 
acid, . 
Anhydrous nitric acid or nitric anhydride. Table of the chief nitrates 
with their common names, and additive and substitutive for- 
mulae, ....... 

Nitrous oxide, . . . . • . . 

Nitric oxide ; rough analysis, of air by nitric oxide, 
Nitrous acid ; preparation of nitrite of potash, . 
Nitric peroxide ; commercial nitrous acid, 

General review of the oxides of nitrogen ; combination in multiple 
proportions ; determination of the composition of the oxides 
of nitrogen ; tabular review of their composition, 
Chlorine. — Its occurrence in nature and extraction from common salt ; 
Weldon's and Deacon's chlorine processes. Striking physical and 
chemical properties of chlorine ; powerful attraction for non-metal- 
lic and metallic elements, ....... 

Relations of chlorine to hydrogen ; synthesis of hydrocholoric acid 
effected by natural and artificial light ; displacement of oxygen 
from water by chlorine ; action of chlorine upon other hydrogen- 
compounds ; substitution of chlorine for hydrogen in organic sub- 
stances ; oxidising action of moist chlorine, 
Bleaching properties of chlorine ; their application, 
Chloride of lime. — Mode of using it for bleaching, and for printing white 
patterns on a coloured ground ; disinfecting properties of chlorine ; 
application of chloride of lime for disinfecting, '.'■'. 



Paragraph 
80 
81 



83 
84 
85 

86 



87 



90 

91 

92 

93 

94 



95 

96 
97 
98 
99 



100 



101 



102 
103 



104 



CONTENTS. XV 

Paragraph 

History of the discovery of chlorine ; phlogiston, . . ,105 

Hydrochloric acid. — Preparation and properties of the gas ; production 
of solution of hydrochloric acid in the alkali works. "Weak acid 
properties of liquefied hydrochloric acid, . . . .106 

Action of hydrochloric acid upon metals ; demonstration of its com- 
position by volume, ...... 107 

Action of hydrochloric acid upon metallic oxides ; formation of 

chlorides, ....... 108 

Molecular weight of hydrochloric acid, . . . .109 

Types of atomic formula? ; atomicity of the elements. — Molecules of hy- 
drochloric acid, water, ammonia, and marsh-gas; monad, dyad, triad, 
and tetrad elements ; graphical representation of atoms, . . 110 

Compounds of chlorine with oxygen, . .. . . .111 

Hypochlorous acid. — Its use for erasing ink ; the hypochlorites ; prepa- 
ration of oxygen from chloride of lime. Chloride of soda, . 112 
Chloric acid. Chlorate of potash ; preparation ; from carbonate of 
potash ; from chloride of potassium. Preparation and properties 
of hydrated chloric acid. Useful applications of chlorate of potash. 
Combustion of chlorate of potash in coal-gas. Coloured fire com- 
positions. Anomalous evolution of heat in the decomposition of 
chlorate of potash, . . . . . . .113 

Perchloric acid. — Explosive properties of the hydrated acid, . .114 

Chloric peroxide. — Its unstable character and powerful oxidising action. 

Euchlorine, . . . . . , .115 

Chlorous acid, . . . . ... . .116 

General review of the oxides of chlorine ; their composition by volume, 117 
Chlorides of carbon. — Preparation of the bichloride or tetrachloride. 
Composition by volume of the chlorides of carbon. Influence of 
the composition by volume of a compound upon its properties. 
Table of the molecular formulae, weights and volumes of the 
chlorides of carbon, . . . . . .118 

Phosgene gas or oxychloride of carbon, . . . . .119 

Chloride of silicon. Chloride of boron, ■> • • .120 

Chloride of nitrogen. — Processes for preparing it ; violent explosive 

character, ........ 121 

Aqua regia. — Chloronitric and chloronitrous gases, . . .122 

Bromine. — Extraction from the waters of mineral springs ; great chemical 

resemblance to chlorine ; hypobromous and bromic acids, . .123 

Hydrobromic acid,. Bromide of nitrogen. Chloride of bromine, . 124 

Iodine. — Extraction from ashes of sea-weed. Characteristic properties of 

iodine and the iodides, . . . . . .125 

Iodic acid. Periodic acid, . . . . . .126 

Hydriodic acid. — Its powerful reducing properties, . . .127 

Iodide of nitrogen.— Explosive character, . ... .128 

Chlorides and bromides of iodine, ..... 129 

Iodide of potassium. — Its preparation. Iodide of iron, . . 130 

Fluorine. — Fluorspar, . . . . . . .131 

Hydrofluoric acid ; etching on glass. Fluorides ; Jcryolite, . . 132 

Fluoride of silicon ; artificial formation of staurolite, . . . 133 

Hydrofluosilicic acid, . . . . . .134 

Fluoride of boron ; fluoboric and hydrofluoboric acids, . . . 135 



XVI CONTENTS. 

Paragraph 

General review of chlorine, bromine, iodine, and fluorine, . .136 

Sulphur. — Its occurrence in nature ; composition of the principal sulphides 
and sulphates found in the mineral kingdom. Extraction of sulphur 
in Sicily. Kenning of sulphur. Distillation of sulphur from pyrites. 
Commercial varieties of sulphur, . . . . .137 

Properties of sulphur ; remarkable transformation by heat ; electro- 
positive and electro-negative sulphur ; soluble -and insoluble 
varieties ; octahedral and prismatic sulphur]; table of the chief allo- 
typic forms of sulphur, . . ■ . . . .138 

Influence of temperature upon the specific gravity of gases and 

vapours ; anomalous expansion of sulphur vapour, ■ . .139 

Uydrosulphuric acid. — Its preparation for laboratory use; preparation of 
sulphide of iron. Properties of sulphuretted hydrogen ; action upon 
metals and their oxides ; blackening of paint, pictures, &c. , by im- 
pure air ; use of sulphuretted hydrogen in analysis ; sulphur acids, 
bases and salts ; action of air upon metallic sulphides, . . 140 

Pur sulphide of hydrogen, . . . . . .141 

Compounds of sulphur with oxygen, . . . . .142 

Sulphurous acid. — Its bleaching and antiseptic properties. Sulphite of 

soda, ......... 143 

Sulphuric acid. — Direct combination of sulphurous acid and oxygen ; 
Nordhausen oil of vitriol ; preparation of anhydrous sulphuric acid ; 
gradual development of the English manufacture of oil of vitriol ; 
experiments illustrating the theory of the process ; preparation of 
oil of vitriol in the laboratory and on the large scale ; plan for 
economising nitric oxide ; commercial varieties of sulphuric acid. 
Properties of oil of vitriol ; its action upon organic substances and 
upon metals. Other hydrates of sulphuric acid, . . .144 

Sulphuric anhydride ; determination of the composition of sulphuric 

acid and oil of vitriol, . . . . . .145 

Sulphates. Action of sulphuric acid upon metallic oxides. Neu- 
tral acid, and double sulphates. Decomposition of sulphates 
by heat and by reducing agents. Table of the chief sulphates, 
with their common names, and additive and substitutive 
formulae, . . . . . . . .146 

Hyposulphurous acid. — Hyposulphite of soda; its preparation and use 
for fixing photographic prints, and for making antimony ver- 
milion, . . . . . . . .147 

Hypo sulphuric or dithionic acid, ..... 148 

Trithionic or sulphuretted hyposulphuric acid, . . . .149 

Tdrathionic or bisulphuvctted hyposulphuric acid, . . . 150 

Peutathionic acid, . . . . . . .151 

Bisulphide of carbon. — Its use in spectrum analysis ;- its diathermanous 
character, resistance to congelation and inflammability ; a starting- 
point for the synthesis of organic compounds. Sulphocarbonates. 
Removal of bisulphide of carbon from coal-gas. Preparation and 
properties of carbonic oxysulphide, . . . .152 

Bisulphide of silicon, . . . . • . .153 

Sulphide of nitrogen. — Its explosive character, . . .154 

Chlorides of sulphur. — Preparation of the subchloride or chloride of 
sulphur. Iodides of sulphur, ..... 



155 



CONTENTS. 



XV11 



Paragraph 

Selenium. — Its extraction from the deposit in the vitriol chambers. Sele- 
nious and selenic acids. Selenietted hydrogen. Chlorides and 
sulphides of selenium, ...... 

Tellurium. — Tellurous and telluric acids ; telluretted hydrogen ; chlorides 
and sulphides of tellurium, 
Review of the sulphur group of elements, comprising sulphur, selenium, 
and tellurium, . ... 

Phosphorus. — Its distribution in nature ; extraction from bones on the 
large and small scales ; action of light on phosphorus. Phosphores- 
cence. Allotropic modifications of phosphorus. Preparation of red 
phosphorus. Precipitation of metals by phosphorus, 
Lucifer matches ; silent matches ; safety matches, 
Armstrong fuze composition, . 
Oxides of phosphorus. — Table of their composition, 
Phosphoric acid. — Its natural sources ; preparation from bones. Phos- 
phoric anhydride. Metaphosphoric, pyrophosphoric, and ortho- 
phosphoric acids, ...... 

Phosphorous acid ; phosphites, .... 

Hypophosphorous acid, 

Suboxide of phosphorus. — Combustion of phosphorus under water, 

Phosphides of hydrogen. — Preparation and properties of phosphuretted 

hydrogen gas, 
Chlorides of phosphorus. — Oxychloride, and sulphochloride of phos- 
phorus ; sulphoxyphosphate of soda. Action of iodine on phos- 
phorus, .... 

Sulphides of phosphorus, 

Action of ammonia upon phosphoric anhydride. Phosphamic acid. 

Phospham. Action of ammonia on oxychloride and penta- 

chloride of phosphorus. Amides of phosphoric acid, 

Arsenic. — Formula? of natural arsenides and arseniosulphides. Extraction 

of arsenic from mispickel. Properties and chemical relations of 

arsenic, ........ 

Oxides of arsenic. Arsenious acid. — Composition of arsenious and 

arsenic acids. Arsenites. Scheele's green," 
Arsenic acid. — Its hydrates. Arseniate of soda, 

Arsenietted hydrogen. — Marsh's test for arsenic. Composition and mole- 
cular formula of arsenietted hydrogen. General review of ammonia, 
phosphuretted and arsenietted hydrogen, .... 

Terchloride of arsenic. Terbromide of arsenic, 
Teriodide and terfluoride of arsenic, 
Sulphides of arsenic. Realgar. King's yellow. 
sulpharsenic acids, .... 

General review of the non-metallic elements.- 

ing to their atomicities. Elucidation of the constitution of compound 
bodies by the doctrine of atomicity, ..... 

Constitution of salts. — Haloid and oxy-acid salts. Difference between 
neutral and normal salts. Criterion of normality. Normal ratios. 
Binary theory of salts. Water-type theory. Constitution of poly- 
basic acids and their salts, . . . . . .179 



Sulpharsenious and 
-Classification accord- 



156 



157 



158 



159 
160 
161 
162 



163 
164 
165 
166 

167 



168 
169 



170 



171 

172 
173 



174 
175 
176 

177 



178 



xvm 



CONTENTS. 



CHEMISTEY OF THE METALS. 



Paragraph 
Hydrate of 
potassium. 



of 



Nitrate 
Chlorate 



Potassium. — Its occurrence in nature. Carbonate of potash, 
potash. Extraction of potassium. Blowpipe test for 
Chloride of potassium. Bicarbonate of potash, 
Sodium. — Extraction of salt. Salt-gardens of Marseilles, 

Manufacture of carbonate of soda from common salt -Soda-ash 
Soda-crystals. Soda-lye. Hydrate of soda, 
Extraction of sodium from the carbonate. Uses of sodium, . 
Borax. Refining of tincal. Crystallisation of borax, 
Silicate of soda. Soluble glass. Artificial stone. Sulphate of soda 
Phosphate of soda, ..... 

Salts of ammonia, ...... 

Sulphate of ammonia, . . . 

Sesquicarbonate of ammonia, ..... 

Hydrochlorate of ammonia ; its dissociation by heat, 
Hydrosulphate of ammonia, ..... 

Lithium. — Lepidolite, petalite, spodumene. Lithia. Carbonate 
lithia. Rubidium. Ccesium, .... 

Spectrum analysis, ...... 

General review of the group of alkali-metals, 
Barium. — Preparation of barium-compounds from heavy spar, 
and hydrate of baryta. Binoxide and chloride of barium, 
of baryta, ........ 

Strontium. — Preparation of nitrate of strontia, .... 

Calci dm.— Carbonate of lime; its various mineral forms. Lime-burning. 
Sulphate of lime. Preparation of plaster of Paris. Chloride of 
calcium, . • . 

Magnesium. — Extraction and properties of the metal. Preparation of 
sulphate and carbonate of magnesia. Chloride of magnesium, 
General review of the metals of the alkaline earths, 
Equivalent and atomic weights of barium, strontium, calcium, and mag- 
nesium. Relation between specific heats and equivalent weights. 
Atomic heats, ....... 

Aluminum. — Minerals containing alumina. Composition of clay. Manu- 
facture of alum. Alumina. Chloride of aluminum, 
Extraction of aluminum from bauxite. Aluminate of soda. Properties 
and uses of aluminum, ...... 

Mineral silicates of alumina. Exchange of isomorphous metals in 
minerals. Natural and artificial ultramarine, 
Glucinum, Thorinum, Yttrium, Erbium, Terbium, Cerium, Lan- 

thanium, Didymium, Zirconium, .... 203-207 

Zinc. — Properties upon which its usefulness depends. Galvanised iron. 
Ores of zinc. Distillation of zinc. English method of extracting the 
metal from its ores. Belgian and Silesian processes. Oxide, sul- 
phate and chloride of zinc, ...... 208 

Cadmium. — Sulphide and iodide of cadmium. Indium, . . . 209 

Uranium, ......... 210 

Iron. — Its occurrence in nature. Ores of iron. Table of composition of 

British iron ores, . . . . . . .211 

Metallurgy of iron. — Its physical properties, .... 212 



180 
181 

182 
183 

184 

185 
186 

187 
188 
189 
190 

191 
192 
193 



194 
195 



196 

197 
198 



199 



200 



201 



202 



CONTENTS. 



XIX 



Paragraph 
English process of smelting clay iron-stone. — Blast-furnace. Chemical 
changes in the blast-furnace. Composition of gas from blast- 
furnace. The hot blast. Composition of slag from the blast- 
furnace, ........ 213 

Cast-iron. — Composition of different varieties of cast-iron. Grey, mot- 
tled, and white iron. Chill-casting, . . . .214 

Conversion of cast-iron into bar-iron. — Eefining. Puddling. Varieties 
of bar-iron. Chemical effect of puddling and forging on cast-iron. 
Composition of tap-cinder. Defects of the puddling process. 
Bessemer's process. Conditions influencing the strength of bar-iron, 21 5 
Manufacture of steel. — The cementation process. Shear steel. Pro- 
duction of cast-steel. Hardening and tempering steel. Case- 
hardening. Malleable cast-iron. Bessemer steel. Spiegel-eisen. 
Homogeneous iron. Puddled steel. Natural or German steel. 
Krupp's cast-steel, . . . . ; .216 

Direct extraction of wrought iron from the ore. — The Catalan process, . 217 
Extraction of iron on the small scale. Sefstrom furnace, . . 218 

Chemical properties of iron. Passive state of iron, . . .219 

Oxides of iron. Ferrous oxide. Ferric oxide. Magnetic oxide of 

iron. Ferric acid, . . . . . . 220 

Protosulphate of iron. Persulphate of iron, . . . .221 

Perchloride of iron, ....... 222 

Equivalent and atomic weights of iron. Varying atomicity of iron. 

Ferrosum and ferricum, ...... 223 

Manganese, . . . . .• . . . 224 

Oxides of manganese. Binoxide, protoxide, sesquioxide, red oxide. 

Manganic acid. Permanganic acid. Permanganate of potash, . 225 
Chlorides of manganese. Eecovery of waste manganese, . . 226 

Cobalt. — Protoxide and sequioxide of cobalt. Chloride and sulphide of 

cobalt, ........ 227 

Nickel. — Oxides, sulphate, and sulphides of nickel, . . . 228 

Chromium. — Preparation of bichromate of potash from chrome-iron, . 229 
Chromic acid. Chromate of potash. Chromat© of lead. Sesquioxide 

of chromium. Protoxide of chromium. Perchromic acid, . 230 

Protochloride and sesquichloride of chromium. Chlorochromic acid. 

Fluoride and sulphide of chromium, . . . .231 

General review of zinc, iron, cobalt, nickel, manganese, and chromium, . 232 
Copper. — Its occurrence in nature, ..... 233 

Ores of copper. Copper pyrites. Malachite. Grey copper ore, . 234 

Smelting of copper-ores. Calcining the ore. Copper smoke. Fusion 
for coarse metal. Calcining the coarse metal. Fusion for white 
metal. Eoasting the white metal. Kefining the blister copper. 
Toughening or poling. Underpoled and overpoled copper. Table 
of products obtained in smelting copper-ores, . . . 235 

Extraction of copper from copper-pyrites in the laboratory, . . 236 

Effect of impurities upon the quality of copper, . . . 237 

Properties of copper, ....... 238 

Effect of sea- water upon copper. Muntz-metal, . . .239 

Danger attending the use of copper vessels in cooking food, . . 240 

Alloys of copper with other metals. — Table of their composition. Brass. 

Bronzing. Aich metal. Sterro-metal, . . . .241 



XX CONTENTS. 

Paragraph 
Oxides of copper. Cupric and cuprous oxides. Quadrantoxide. Cupric 

acid, • 242 

Sulphate of copper. Carbonates and silicates of copper, . . 243 

Chlorides of copper. Oxychloride ; Brunswick green. Cuprous 

chloride, ........ 244 

Sulphides of copper. Extraction of copper by kernel-roasting. Sub- 
sulphide of copper. Copper pyrites. Phosphide of copper, . 245 
Lead. — Its useful qualities. Ores of lead. Galena, . . . 246 

Smelting of galena. Old English process. Ecohomico-furnace, . 247 

Improving process for hard lead, ..... 248 

Extraction of silver from lead. — Pattinson's process for concentrating 

silver in lead, ....... 249 

Cupellation of argentiferous lead. Sprouting of silver, . .250 

Extraction and cupellation of lead in the laboratory, . .251 

Uses of lead. Type metal. Shot. Solder, . . . .252 

Lead pyrophorus. Oxides of lead. Litharge. Minium. Peroxide 

of lead, ........ 253 

Manufacture ofivhite lead. — Dutch process. Pattinson's process. Car- 
bonate, sulphate, and phosphate of lead, . . . . 254 

Chloride and oxychloride of lead. Turner's yellow. Iodide of lead, 255 
Sulphides, chlorosulphide, and selenide of lead, . . .256 

Thallium. — Its discovery by the spectroscope. Its position among the 

metals, ........ 257 

Silver. — Extraction of silver from copper by liquation. Amalgamation 
of silver-ores. Standard silver. Plating and electro-plating. Silver- 
ing glass. Preparation of pure silver, . . . .258 

Properties of silver, . . . . • . . . . 259 

Oxides of silver. Preparation and uses of nitrate of silver. Perma- 
nent ink, ........ 260 

Chloride of Silver. Eecovery of silver from photographic baths. 

Subchloride, bromide, iodide, and sulphide of silver, . .261 

Mercury. — Extraction from cinnabar at Idria and Almaden. Purification 

of mercury, . . . . . . . 262 

Medicinal preparations of metallic mercury, .... 263 

Uses of mercury. Silvering looking-glasses. Amalgams, . . 264 

Mercurous and mercuric oxides. Mercuramine, . . . 265 

Mercurous and mercuric nitrates and sulphates, . . . 266 

Chlorides of mercury. Corrosive sublimate. White precipitate, . 267 

Calomel. Its preparation and properties. Mercurous and mercuric 

iodides, ........ 268 

Sulphides of mercury. Preparation of vermilion, . . . 269 

Bismuth. —Extraction and properties. Fusible alloy, . . . 270 

Bismuthous and bismuthic oxides. Bismnthic acid, . . . 271 

Trisnitrate of bismuth or flake-white. Pearl-white. Terchloride of 

bismuth. Bismuthous and bismuthic sulphides, . . . 272 

Antimony. — Extraction of regulus of antimony. Amorphous antimony, 273 
Oxides of Antimony. Antimonic acid. Antimoniate, metantimon- 

iate and bimetantimoniate of potash, .... 274 

Antimonietted hydrogen, ...... 275 

Terchloride and pentachloride of antimony, . . . .276 

Sulphides of antimony. Mineral kermes. Schlippe's salt, . .277 



CONTENTS. XXI 

Paragraph 

Tin. — Cornish treatment of tin ores. Extraction and purification of tin, 278 
Physical properties of tin. Manufacture of tin-plate. Tinning of 

copper vessels, . . . - . . . . 279 

Alloys of tin. Solder. Gun-metal. Bronze. Bell-metal, . . 280 

Oxides of tin. Stannous oxide. Stannic acid. Preparation of stan- 

nate of soda. Metastannic acid, . . . .281 

Protochloride of tin or tin-crystals. Perchloride or nitromuriate of 

tin. Pink salt, . . . . . . 282 

Sulphides of tin. Preparation of mosaic gold, . . .283 

Titanium. — Titanic acid ; its extraction from iron-sand. Other com- 
pounds of titanium, ....... 284 

Tungsten. — Preparation of tungstate of soda from wolfram. Dialysed 

tungstic acid. Oxides, chlorides, and sulphides of tungsten, . 285 

Molybdenum. — Preparation of molybdate of ammonia, . . . 286 

Vanadium. — Preparation of vanadic acid from vanadiate of lead, . 287 

Niobium. — Tantalum, ....... 288 

Platinum. — Treatment of platinum ores by the wet and dry processes. 

Spongy platinum. Platinum black, .... 289 

Platinous and platinic oxides. Preparation of perchloride of platinum. 

Its double salts with alkaline chlorides. Platinous chloride. Its 

behaviour with ammonia. Platosamine and platinamine, . . 290 

Palladium. — Its separation from platinum ores, . . .291 

Ehodium. — Extraction of the metal from rhodio-chloride of sodium, . 292 

Osmium. — Osmic acid. Chlorides of osmium, .... 293 

Ruthenium. — Oxides of ruthenium. Ruthenic acid, . . . 294 

Iridium. — Extraction from the native osmiridium alloy, . . . 295 

Tabular view of the analysis of platinum ores. Summary of the group 

of platinoid metals, . . . . . .296 

Gold. — Washing for gold-dust. Smelting of auriferous ores ; with lead ; 
with pyrites. Amalgamation of gold ores. Standard gold. Testing 
and assaying gold, . ...... 297 

Physical properties of gold. Gold leaf. Ruby gold. Manufacture of 

goldthread. Gilding, ..."... 298 
Oxides and chlorides of gold. Fulminating gold. Sel cVor. Purple of 

Cassius, ........ 299 

Chemical principles of the manufacture of glass. — Window glass. 
Plate glass. Crown and flint glass. Production of coloured 
glasses, ......... 300 

Chemistry of the manufacture of pottery and porcelain. — Sevres 
porcelain. English porcelain. Stone-ware. Earthenware. Bricks. 
Dinas fire-bricks. Blue bricks, . . . . 301 

Chemistry of building materials. — Varieties of building stones. Free- 
stone. Portland and Bath stones. Magnesian limestones. Test of 
resistance of building stones to frost, ..... 302 

Mortar. Hydraulic cements. Concrete, .... 303 

Gunpowder. — Nitre or saltpetre. Grough nitre. Conversion of nitrate 
of soda into nitrate of potash. Artificial production of nitre in the 
nitre-heaps. Saltpetre-refining, ..... 304 

Properties of saltpetre. Relation to combustible bodies, . . 305 

Charcoal for gunpowder. — Composition of charcoal prepared at different 

temperatures, ....... 306 



XX11 CONTENTS. 

Paragraph 
Sulphur for gunpowder. — Tests of its purity. Functions of sulphur in 

gunpowder, ....... 307 

Manufacture of gunpowder — Incorporation. Pressing. Granulating 

or corning. Glazing, ...... 308 

Properties of gunpowder. — Effects of air, water, and heat upon powder, 309 
Products of explosion of gunpowder. — Difference in results obtained by- 
different experimenters. Most recent experiments, . . 310 
Calculation of the force of fired gunpowder. — Gas furnished by calcula- 
tion from a given quantity of powder. Temperature of the gas at 
instant of explosion. Specific heats of the products of explosion. 
Expansion of the gas by heat. Mechanical equivalent of gun- 
powder. Effect of size of grain on the firing of powder. Blasting- 
powder, . . . . . . . .311 

Effect of variations of atmospheric pressure on the combustion of gun- 
powder. — Manufacture of gunpowder in the laboratory, . . 312 
Chemistry of Fuel. — Calorific value of fuel calculated. Theoretical and 
actual calorific values. Difference between calorific value and calori- 
fic intensity. Calculation of the calorific intensity of carbon burning 
in oxygen and in air. Calculation of the calorific intensity of hydrogen 
burning in air. Calculation of the calorific intensity of fuel contain- 
ing carbon, hydrogen, and oxygen. Theoretical and actual calorific 
intensities. Waste of heat in furnaces. Economy of heat in Siemens' 
regenerative furnace. Table of composition, calorific values, and in- 
tensities of ordinary fuels, . . . . . .313 



OEGAOTC CHEMISTEY. 

Introductory, . . . . . . . . 314 

Cyanogen and its Compounds. — History of cyanogen, . . . 315 

Yellow prussiate of potash or ferrocyanide of potassium. Prussian blue. 
Hydroferrocyanic acid. Hydrocyanic or prussic acid. Cyanide of 
mercury, . . . . . . . 316 

Preparation and properties of cyanogen. Cyanide of potassium. Cyan- 
ate of potash. Cyamelide. Hydrated cyanic acid. Sulphocyanide 
of potassium. Hydrosulphocyanic acid. Liebig's test for prussic 
acid, . . . . . . . .317 

Keel prussiate of potash or ferricyanide of potassium. Turnbull's blue. 

Ferri cyanogen and other compound cyanogen radicals, . . 318 

Chlorides of cyanogen. Cyanuric acid. Cyanide of phosphorus, . 319 

Nitroprussides. Hadow's and Stadeler's investigation of their constitu- 
tion. Economical preparation of nitroprusside of sodium, . 320 
The fulminates. — Preparation of fulminate of mercury. Its properties. 
Percussion cap composition. Fulminate of silver. Experiments 
with the fulminates. Chemical constitution of the fulminates. 
Fulminurates or isocyanurates, . . . . .321 

Products of the destructive distillation of coal. — Manufacture of 

coal-gas. Composition of coal-tar, ..... 322 

Coal-naphtha. Separation of its constituents by fractional distillation, . 323 
Benzole. Chloride of benzole. Trichlorhydrine of phenose. Phenose, 324 
Aniline. Its preparation from nitrobenzole. Production of colouring 

matters from aniline, . . • ... . 325 



CONTENTS. 



XX111 



Paragraph 

Coal-tar dyes.—Mimve or aniline-purple. Mauveine. Magenta or ani- 
line-red. Eosaniline and its salts. Leucaniline. Chrysaniline or 
aniline-yellow. Triphenylic rosaniline or aniline-blue, Ethyl- 
iodate of tri-ethyl-rosaniline. Hydrocyan-rosaniline, 
Chemical constitution of aniline. Formation from phenic acid and 

ammonia. Picoline. Quinoline, . . 

Benzole series of homologous hydrocarbons. Their relation to the 
aromatic acids. Homologous nitro-compounds and bases derived 
from them, ....••• 

Carbolic acid. Preparation from the dead-oil of coal-tar. Examina- 
tion of commercial carbolic acid, .... 

Carbazotic or picric acid. Chloropicrine. The phenyle series. Kre- 
sylic acid, . . ... 

Naphthaline. Substitution products from naphthaline. Phthalic 
acid. Connection of naphthaline with the phenyle series. Para- 
naphthaline. Chrysene. Pyrene, .... 

Products of the destructive distillation op wood. — Proximate 

constituents of wood. Cellulose. Lignine. Composition of different 

woods. Products of the action of heat upon wood, . 

Wood-naphtha or methylic alcohol. Purification. Methyle- compounds 

Oil of winter-green. Metamerism illustrated by formiate of methyle 

and acetic acid, ...... 

Parafnne. Extraction from wood-tar. Paraffine oil. Stockholm tar 

Petroleum. Eangoon tar. Bitumen or asphaltum, 
Oil of turpentine and substances allied to it. — Colophony. Isomeric 
modifications of turpentine. Artificial camphor, 
The turpentine series of hydrocarbons. Essential oils, 
Camphors. Common camphor. Borneo camphor, . 
Balsams. Balsam of Peru. Storax. Styrole and metastyrole, 
Eesins. Copal. Lac. Amber. Varnishes. Benzoin. Benzoic 
acid, ....... 

Oil of bitter almonds and its derivatives — Benzoyle series. — 

Formation of bitter almond oil. Amygdaline. -Emulsine. Benzoine 

Benzoyle. Benzoic anhydride, . . . 

Oil of cinnamon. — Cinnamic acid. Cinnamyle. Cummin oil. Cuminic 

acid, ........ 

Salicine and its derivatives — Glucosides. — Saligenine ; its chlori- 
nated derivatives. Salicylic acid. Oil of spiraea. Benzoyle-salicyle, 
Populine or benzoyle-salicine. Phloridzine. Quercitrine. Esculine. 
Paviine. Saponine. Picrotoxine, .... 

Essential oils containing sulphur — Allyle series. — Formation 
of essence of mustard. Myronicacid. Iodide of allyle. Artificial 
formation of essences of mustard and garlic. Allylic alcohol. Ally- 
lene, 
Gum-resins, Caoutchouc. — Vulcanised caoutchouc. Gutta percha, 
Gums. — Arabine. Mucic acid. Gum tragacanth, 
Starch. — Manufacture of starch. Composition of the potato ; of wheat 
of rice. Properties of starch. Sago. Tapioca, 
Conversion of starch into dextrine and grape-sugar, . 
Germination of seeds — Malting. — Action of diastase on starch. Com- 
position of malted and unmalted barley, and of malt-dust, 



326 



327 



328 



329 



330 



331 



332 



333 

334 

335 
336 
337 
338 

339 



340 



341 



342 



343 



344 
345 
346 

347 

348 

349 



XXIV CONTENTS. 

Paragraph 

Brewing. — Composition of the hop. Nature of yeast. Alcoholic fer- 
mentation. Composition of beer. Viscous fermentation, . . 350 
Acetifcation. — Manufacture of vinegar. The quick vinegar process, . 351 
Bread. — Composition of gluten. Process of bread-making. Aerated 

bread. Leaven. New and stale bread, .... 352 

The Sugars. — Production of sugar from cotton, paper, and other varieties 
of cellulose. Action of sulphuric acid on cellulose. Vegetable parch- 
ment. Sugar of fruits or fructose. Conversion of cane-sugar into 
fructose, . . ... . . . . 353 

Extraction of cane-sugar. —Vacuum pans. Sugar refining, . . 354 

Beetroot sugar. Maple sugar. Sugar-candy. Barley-sugar. Caramel, 355 
Chemical properties of the sugars. Compounds of sugar with bases. 
Action of solutions of the sugars upon polarised light. Ethyle- 
glucose, ........ 356 

Mannite. Glycyrrhizine, . . . . . .357 

Gun-cotton and substances allied to it. — Pyroxyline. Preparation 

of gun- cotton in the laboratory, ..... 358 

Manufacture of gun-cotton. — Abel's process. . . . . 359 

Chemical composition of gun-cotton. Trinitro-cellulose. Keconver- 

sion of gun-cotton into ordinary cotton, . . . 360 

Products of the explosion of gun-cotton. Explosion of loose and con- 
fined gun-cotton. Karolyi's experiments. Effects of gun-cotton 
and gunpowder compared, . . . . .361 

Properties of gun-cotton compared with those of gunpowder, . 362 

Behaviour of gun-cotton with solvents, .... 363 

Collodion-cotton. Action of weak nitro-sulphuric mixtures upon 
cotton. Preparation of soluble cotton for collodion. Process 
for making balloons of collodion, .... 364 

Xyloidine. Nitromannite, ...... 365 

Wine and spirits. — Preparation and composition of wines. Proportion 

of alcohol in wines, ....... 366 

Distilled spirits. Brandy, whisky, gin, &c. Potato-spirit, . . 367 

The Alcohols and their derivatives. — General formula of alcohols of 
the vinic class. Table ' of the vinic or ethylic class of alcohols, with 
their sources, common names, and formulae Gradation in properties 
of the homologous alcohols. Table of their boiling points and vapour 
densities. Chemical definition of an alcohol. General formulae for 
the derivation of an aldehyde, an acid, and an ether from an alcohol. 
Table of the acetic series of acids with their sources and formulae. 
General description of the acetic series. The olefines or olefiant gas 
series of hydrocarbons. Polymerism, ..... 368 

Alcohol as the type of its class. Preparation of absolute alcohol, . 369 

Ether. Continuous etherifying process, Preparation of ethylic iodide, 370 
The alcohol-radicals. Isolation of ethyle. General formula of alcohol- 
radicals. Duplex constitution of the alcohol-radicals. Hydrides of 
alcohol-radicals, or marsh-gas hydrocarbons, . . .371 

Compound ethers. — Oxalic ether. Oxalovinic acid. Acetic ether. 
Nitrous ether. Nitric ether. Hydroxylamine prepared from nitric 
ether. Perchloric ether. Boracic and silicic ether. Carbonic 
ether. Formation of subcarbonate of ethyle from chloropicrine. 
Phosphovinic acid. True sulphuric ether. Oil of wine, . . 372 



CONTEXTS. 



XXV 



Paragraph 
Sulphovinic or sulpliethylic acid. Its preparation, . . . 373 

Vinic acids not formed by monobasic acids, .... 374 

Theory of ether ification. — Formation of double ethers, . . 375 

Water-type view of alcohols and ethers. Potassium and sodium 

alcohols. Thallium alcohol, . . . . . 376 

Sulphuretted derivatives of the alcohols. Mercaptan, . . 377 

Cyanides of alcohol- radicals. Their relation to the acids of the acetic 

series, ........ 378 

Kakodvle-series — Organo-metallic bodies. — Alcarsin. Chloride of 

kakodyle. Kakodylic acid. Cyanide of kakodyle, . . 379 

Preparation and properties of zinc-ethyle. Zinc-methyle. Zinc-amyle. 
Potassium-ethyle. Sodium-ethyle. Arsenio-dimethyle or kako- 
dyle. Arsenio-diethyle, or ethyle-kakodyle, . . . 380 
Arsenio-trimethyle. Arsenio-triethyle. Stibethyle. Mercuric methide. 

Aluminum ethide. Triborethyle. Boric methide. Silicium-ethyle, 381 
Table of the compounds of alcohol-radicals with inorganic elements ; 
with their formulae and inorganic types. Constitution of the 
organo-metallic radicals, ...... 382 

Organic alkaloids — Ammonias. — Table of the alkaloids with their 

sources and formula?. Theories of the constitution of the alkaloids, 383 
Ethylated ammonias and their derivatives. — Ethylamine. Diethyla- 
mine. Triethylamine. Hydrate of tetrethylium. Complex ammo- 
nias, ........ 384 

Investigation of the constitution of the alkaloids, . . . 385 

Poly-ammonias ; their constitution, . .• . . . 386 

Diamines. Ethylene-diamine. Aromatic diamines. Paraniline, . 387 
Triamines. Carbotriamine. Synthesis of guanidine. Melaniline. 

Aniline colours probably triamines, .... 388 

Tetramines. Tetrammonium-bases, .... 389 

Ammonia-bases formed in putrefaction and destructive distilla- 
tion, ........ 390 

Ammonias and ammonium bases containing phosphorus, arsenic, and 

antimony, . . . . r . . . 391 

Platammonium-compounds, ...... 392 

• Amides. Oxamide. Oxamic acid, . . . . .393 

Nitriles. Imides, ....... 394 

Constitution of the amides, . . . . . . 395 

Metal-amides. — Tripotassamide. Zinc-amide. Zinc-acetimide, . 396 

Derivatives of the alcohols. — Chloroform. Chloral, . . 397 

Perfume-ethers. — Pine-apple and pear essences. Apple-oil, . . 398 

Aldehydes. — Preparation and properties of vinic aldehyde. Constitu- 
tion and synthesis of the aldehydes. Action of aldehydes on the 
ammonia-bases, . ...... 399 

Acetones or ketones. — Synthesis of acetic acetone. Methyle-valeryle 

acetone. Metacetone, - . . . . . . 400 

The essential oils regarded as aldehydes, . ■ . . 401 

Polyatomic alcohols. Glycol. — Preparation and properties of glycol. 
Glycolic acid ; its relation to oxalic acid. Lactic series of acids. 
Conversion of the oxalic into the lactic series. Synthesis of leucic 
acid. Conversion of a diatomic into a mon atomic alcohol. Water- 
type view of polyatomic alcohols, ..... 402 



XXVI CONTENTS. 

Paragraph 

Acetic acid — The fatty acid series. — Acetates. Acetone. Chlora- 

cetic acids. Synthesis of acetic acid, .... 403 

Anhydrides of organic acids. — Acetic anhydride. Duplex constitution 
of the anhydrides. Peroxides of organic radicals. Acetic and 
benzoic peroxides, ....... 404 

Formic acid. Synthesis of formic acid. Furfurole. Butyric acid. 
Synthetical formation of acids of the acetic series. Ethacetic, 
dimethacetic, or butyric acid. Dieth acetic acid. Ethylated and 
methylated acetones. Valerianic acid, ... 405 

Separation of volatile acids by the method of partial saturation, . 406 
Soap. — Composition of the neutral fats. Stearine, oleine, palmi- 
tine. Action of alkalies upon them. Preparation of the fatty 
acids, ........ 407 

Candles. — Decomposition of fats by sulphuric acid. Saponification by 

superheated steam, ...... 408 

Synthesis of natural fats. — Glycerides. Water-type view of glycerine 

or glyceric alcohol, . . . . . . 409 

Properties of glycerine. Acroleine. The acrylic series of acids. The 

allyle series, . . . . . . . 410 

Relation between glycerine and mannite. Mannite-glycerides. Stearic 

glucose. Gluco-tartaric acicl, . . . . .411 

Nitroglycerine. — Its preparation and properties, . . .412 

Oils and Fats. — Palmitine. Oleine. Margarine. Oleic acid. Sebacic 
acid. Dibasic fatty acid series. Linseed oil. Drying oils. Castor 
oil. Butter. Spermaceti. Wax. Table of the neutral fats and 
fatty acids, with their formulas, sources, and fusing-points, . . 413 

Vegetable acids. — Oxalic acid. Its manufacture from saw-d ust. Con- 
stitution of the oxalates, . . . . . .414 

Tartaric acid. Preparation from cream of tartar. Tartar-emetic. Con- 
version of tartaric into succinic and malic acids, . . .415 
Eacemic acid. Hemihedrism of the tartrates. Dextrotartaric and laevo- 

tartaric acids. Analysis and synthesis of racemic acid, . . 416 

Citric acid. Preparation from lemon-juice, Conversion of citric acid 

into acetic and butyric acids, . . . . .417 

Malic acid. Extraction from rhubarb and from mountain ash berries. 

Sorbic and parasorbic acids. Asparagine, . . .418 

Tannic acid. Preparation of ink. Tanning of hides. Morocco. Kid. 

Wash-leather. Buckskin, ... . . . .419 

Gallic acid. Its formation from tannic acid. Pyrogallic acid. Analysis 

of air by potash and pyrogalline, ..... 420 

Vegetable alkaloids. — Extraction of the alkaloids from opium. Mor- 
phine, codeine, narcotine. Meconic acid, . . . . 421 

Extraction of quinine from Peruvian bark. Quinoidine. . Quinic acid. 

Kinone and hydrokinone, . . . . . . 422 

Theine or caffeine. Composition of coffee and tea. Extraction of caffeine 
from them. Theobromine. Cocoa and chocolate. Methyle-theo- 
bromine or caffeine, . . . . . .423 

Strychnine. Extraction from nux-vomica. Brucine. Detection of 

small quantities of strychnine. Curarine, .... 424 

Nicotine. Extraction from tobacco. Composition of tobacco. Pre- 
paration of snuff ....... 425 



CONTENTS. XXVii 

Paragraph 

Vegetable colouring matters. — Chlorophyll. Phylloxanthine. Phyl- 

locyanine. Colouring matters of fiowers. Cyanine. Saffron. Saf- 

flower ; carthamine. Aimatto ; bixine. Weld ; luteoline. Dye-woods. 

Madder. Eubian. Alizarine. Artificial alizarine. Turmeric, . 426 

Colouring matters prepared from lichens. — Litmus, archil, cudbear. 

Orcine. Orceine. Azolitmine. Erythrite, 



reduced 



427 



428 
429 

430 
431 



Indigo. — Preparation of indigo blue. Indican. White or 

indigo. Dyeing with indigo, 
Animal colouring matters. — Lac. Carmine, 

Dyeing and calico-printing. — Use of mordants. Dyeing red, blue, 
yellow, brown, black, .... 

Printing in patterns. Resists and discharges, 
Animal chemistry. — Special difficulties attending its study. CJi emistry 
of milk. — Cream. Preparation of butter. Coagulation of milk. 
Preparation of lactic acid. Conversion of lactic into propionic acid. 
Preparation of cheese. Caseine. Legumine. Sugar of Milk. Com- 
position of milk from different animals. Adulterationof milk, . 432 
Chemistry of blood. — Composition of blood globules. Colouring matter 
of blood. Composition of liquor sanguinis. Albumen. Fibrine. 
Proteine. Eggs, ....... 433 

Composition of flesh. — Kreatine. Inosite or sugar of flesh. Cooking 

of meat, ........ 434 

Gelatine. Chondrine. Manufacture of glue. Composition of wool 

and silk, ........ 435 

Chemistry of urine. — Urea. Artificial formation of urea, . . 436 

Constitution of urea. Ethyl-urea. Ureides, . . .437 

Uric acid. Alloxan. Alloxantine. Murexide, . . . 438 

Hippuric acid ; its relation to benzoic acid. Glycocoll. Average 

composition of human urine, . . . . .439 

Chemistry of vegetation. — Components of the food of plants ; their 
sources. Process of formation of a fertile soil from a barren rock. 
Action of manures. Fallowing. Rotation of crops. Growth of 
plants from seeds. Ripening of fruits. Pectose. Pectin e. Pectic 
and pectosic acids. Restoration of the elements of plants to the air. 
Preservation of wood from decay, ..... 440 

Nutrition of animals. — Chemistry of digestion. Pepsine. Composi- 
tion of bile. Taurine. Cholesterine. Chemistry of the circulation. 
Composition of food, ....... 441 

Changes in the animal body after death. — Restoration of its elements 

to the earth and air. Nature of putrefaction, . . . 442 



INTRODUCTION, 



1. Chemistry describes the properties of the different particles of which 
all kinds of matter are composed, and teaches the laws which regulate 
their union with, or separation from, each other. 

Matter is anything which possesses weight. Matter is chemically 
divided into two great classes — elements and compounds. 

An Element is that which has not been found divisible into more than 
one kind of matter. 

A Compound consists of two or more elements held together by chemi- 
cal attraction. 

Chemical Attraction is the force which causes different kinds of 
matter to unite, in order to form a new kind of matter. 

Chemical Combination is the operation of chemical attraction. 

Cliemical Decomposition is the separation of two or more kinds of 
matter previously held together by chemical attraction. 

2. The elements known at present are sixty-four in number, and are 
divided into metallic and non-metallic elements. 



The Non-Metallic Elements are (15). 



Oxygen. 


Sulphur. 


JFluorine. 


Hydrogen. 


Selenium. 


Chlorine. 


Nitrogen. 


Tellurium. 


Bromine. 


Carbon. 


Phosphorus. 


Iodine. 


Boron . 


Arsenic* 




Silicon. 







The Metals are (49). 



Ccesium. 

Rubidium. 

Potassium. 

Sodium. 

Lithium. 

Barium. 

Strontium. 

Calcium. 

Magnesium. 


Aluminum. 

Glucinum. 

Zirconium. 

Thoriuum. 

Yttrium. 

Erbium. 

Terbium. 

Cerium. 

Lanthanum. 

Didymium. 

Niobium. 


Zinc. 

Nickel. 

Cobalt. 

Iron. 

Manganese. 

Chromium. 

Cadmium. 

Uranium. 

Indium. 


Copper. 
Bismuth. 
Lead. 
ThaUium. 

Tin. 

Titanium. 

Tantalum. 

Molybdenum. 

Tungsten. 

Vanadium. 

Antimony. 


Mercury. 

Silver. 

Gold. 

Platinum. 

Palladium. 

Rhodium. 

Ruthenium. 

Osmium. 

Iridium. 



The strict definition of a metal will be given hereafter. 

Many of these elements are so rarely met with, that they have not 



* In many English chemical works arsenic is classed 
resembles in some of its properties. 



among the metals, which it 



enibJ 



2 INTRODUCTION. 

received any useful application, and are interesting only to the profes- 
sional chemist. This is the case with selenium and tellurium, among the 
non-metallic elements, and with a large number of the metals. 

The following list includes those elements with which it is important 
that the general student should become familiar, together with the 



symbolic letters by which it is customary 
of brevity, in chemical writings. 



to represent them, for the sake 



Non- Metallic Elements of practical importance (13). 



Oxygen, 
Hydrogen, 
N itrogen, 
Carbon, 



H 

N 
C 


Sulphur, 

Phosphorus, 
Arsenic, 


S 

P 

As 


Fluorine, 
Chlorine, 
Bromine, 
Iodine, 


F 
CI 

Br 
I 


Boron, 
Silicon 


B 

Si 











Metallic Elements of practical importance (26). 



Potassium, 


K 


(Kalium. ) 


Cadmium, 


Cd 




Sodium, 


Na 


(Natrium. ) 


Uranium, 


U 




Barium, 


Ba 




Copper, 


Cu 


(Cuprum.) 


Strontium, 


Sr 




Bismuth, 


Bi 




Calcium, 


Ca 




Lead, 


Pb 


(Plumbum. ) 


Magnesium, 


Mg 




Tin, 


Sn 


(Stannum. ) 


Aluminum, 


Al 




Titanium, 


Ti 




Zinc, 
Nickel, 


Zn 

Ni 




Tungsten, 


W 


(Wolframium.) 




Antimony, 


Sb 


(Stibium. ) 


Cobalt, 


Co 




Mercury, 


Hg 


( Hydrargyruv i. ) 


| Iron, 


Fe- 


(Ferrum. ) 


Silver, 


Ag 


(Argentum.) 


Manganese, 


Mn 




Gold, 


Au 


(Aurum.) 


Chromium, 


Cr 




Platinum, 


Pt 





Although the 39 elements here enumerated are of practical importance, 
many of them derive their importance solely from their having met with 
useful applications in the arts. The number of elements known to play 
an important part in the chemical changes concerned in the maintenance 
of animal and vegetable life is very limited. 

Elements concerned in the Chemical Changes taking place in Life. 



Non-Metallic. 


Metallic. 


Oxygen . Sulphur. 


Potassium. Aluminum. 


Hydrogen. 

Nitrogen. Phosphorus. 

Carbon. 

Chlorine. 
Silicon. Iodine. 


Sodium. 

Iron. 
Calcium. Manganese. 
Magnesium. 



These elements will, of course, possess the greatest importance for those 
who study Chemistry as a branch of general education, since a knowledge 
of their properties is essential for the explanation of the simplest chemical 
changes which are daily witnessed. 

The student who takes an interest in the useful arts will also acquaint 
himself with the remainder of the 39 elements of practical importance, 



INTRODUCTION. 3 

whilst the mineralogist and professional chemist must extend his studies 
to every known element. 

By far the greater proportion of the various materials supplied to us by 
animals and vegetables consists of the four elements — oxygen, hydrogen, 
nitrogen, and carbon ; and if we add to these the two most abundant 
elements in the mineral world, silicon and aluminum, we have the six 
elements composing the bulk of all matter. 

The symbols of the chemical elements represent, as will be explained 
hereafter, definite relative proportions by weight, or chemical units of the 
elements ; thus represents a chemical unit of oxygen, and C a chemical 
unit of carbon. 

To express a number of chemical units of any element, it is usual to 
place a numeral below and to the right of the symbol ; thus 2 represents 
two chemical units of oxygen. 

The mere contact or mixture of substances is expressed by the sign + ; 
thus, C + 2 implies that a chemical unit of carbon has been brought into 
contact with two chemical units of oxygen. 

But when the elements are chemically combined they are placed side 
by side ; thus C0 2 represents carbonic acid gas ; CaO represents lime. 

To indicate that two compound bodies have combined to form a new 
compound, a point or a comma is placed between them ; thus CaO.C0 2 
represents the compound of lime with carbonic acid, known as carbonate 
of lime or chalk. 

3. Compound substances are commonly classified by the chemist into 
Organic and Inorganic compounds ; and although it is impossible strictly 
to define the limits of each class, the division is a convenient one for the 
purposes of study. 

Organic substances may be defined as those for which we are indebted 
to the operation of animal or vegetable life, such as starch, sugar, &c. 

Inorganic substances are obtained from the mineral world without the 
intervention of life ; as common salt, alum, &c. 

Organic substances always contain carbon, generally also hydrogen and 
oxygen, and very frequently nitrogen. 



INOEGANIC CHEMISTEY. 



CHEMISTEY OF THE NON-METALLIC ELEMENTS 
AND THEIR COMPOUNDS. 



WATEK. 

4. A century has not yet elapsed since water ceased to be regarded as 
an elementary form of matter. It was first resolved into its constituent 
elements, hydrogen and oxygen, by subjecting it to the influence of the 
voltaic current, which decomposes or analyses the water by overcoming 
the chemical attraction by which, its elements are held together. 

An arrangement for this purpose is represented in fig 1. 




Pig. 1.— Electrolysis of water. 

The glass vessel A contains water, to which a little sulphuric acid has been added to 
increase its power of conducting electricity, for pure water conducts so imperfectly that 
it is decomposed with great difficulty. B and C are platinum plates bent into a cylin- 
drical form, and attached to stout platinum wires, which are .passed through corks in 
the lateral necks of the vessel A, and are connected by binding screws with the copper 
wires D and E, which proceed from the galvanic battery G. H and are glass cylin- 
ders with brass caps and stop-cocks, and are enlarged into a bell-shape at their lower 
ends for the collection of a considerable volume of gas. These cylinders are filled 
with the acidulated water, by sucking out the air through the opened stop-cocks ; on 
closing these, the pressure of the air will of course sustain the column of water in 
the cylinders. G is a Grove's battery, consisting of five cells or earthenware vessels 
(A, fig. 2) filled with diluted sulphuric acid (one measure of oil of vitriol to four of 
water). In each of these cells is placed a bent plate of zinc (B), which has been 



ELECTEOLYSIS OF WATER. 



amalgamated or rubbed with mercury (and diluted sulphuric acid) to protect it from 
corrosion by the acid when the battery is not in use. Within the curved portion of 





Fig. 2. 

this plate rests a small flat vessel of unglazed earthenware (C), filled with strong 
nitric acid, in which is immersed a sheet of platinum foil (D. The platinum (D) of 
each cell is in contact, at its upper edge, 
with the zinc (B) in the adjoining cell (fig. 
3), so that at one end (P, fig. 1) of the 
battery there is a free platinum plate, and at 
the other (Z) a free zinc plate. These plates 
are connected with the wires D and E by 
means of the copper plates L and K, attached 
to the ends of the wooden trough in which 
the cells are arranged. The wire D (fig. 1), 
which is connected with the last zinc plate 
of the battery, is often called the ' £ nega- 
tive pole ;" whilst E, in connexion with 
the last platinum plate, is called the "positive 
pole. " 

When the connexion is established by means of the wire D and E with the "de- 
composing cell" (A), the "galvanic current" is commonly said to pass along the 
wire E to the platinum plate C, through the 
acidulated water in the decomposing cell, to the 
platinum plate B, and thence along the wire D back 
to the battery. 

A very elegant apparatus (fig. 4) has been 
devised oy Dr Hofmann for exhibiting the de- 
composition of water by the galvanic current. 
The water displaced by the gases accumulating 
in the tubes h, o collects in the bulb b upon the 
longer branch, and exerts the pressure necessary 
to force the gases out when the stop-cocks are 
opened. The stop-cocks, being made of glass, are 
not corroded by the acid. 

5. During this " passage of the current" 
(which is only a figurative mode of express- 
ing the transfer of the electric influence), 
the water intervening between the plates B 
and C is decomposed, its hydrogen being 
attracted to the plate B (negative pole), 
and the oxygen to the plate C (positive 
pole). The gases can be seen adhering in 
minute bubbles to the surface of each plate, 
and as they increase in size they detach 
themselves, rising through the acidulated 
water in the tubes H and 0, in which the 
two gases are collected. 

Since no transmission of gas is observed b 




Electrolysis of water. 



tween the two plates, it is 
evident that the H and separated at any given moment from each plate 
do not result from the decomposition of one particle of water, but from 



ELECTROLYSIS OF WATER. 



two particles, as represented in fig. 5, where. A represents the particles of 
water lying between the plates P and Z before the " current" is passed, 
and B the state of the particles when the current has been established. 
P is (the positive pole) in connexion with the last platinum plate of the 
battery", and Z is (the negative pole) in connexion with the last zinc 
plate. 









































c 





h 


H 


H 


// 


fi 


ft 


// 


» 




+ 


-*- 


+ 


+ 


+ 


■*■ 


+■ 


+ 





Fig. 5. 

The signs + and - made use of in B refer to a common mode of account- 
ing for the decomposition of water by the battery, on the supposition that 
the oxygen is in a negatively electric condition, and therefore attracted by 
the positive pole P \ whilst the hydrogen is in a positively electric condi- 
tion, and is attracted by the negative pole Z. 

The decomposition of compounds by galvanic electricity is termed elec- 
trolysis* When a compound of a metal with a non-metal is decomposed 
in this manner, the metal is usually attracted to the (negative) pole in 
connexion with the zinc plate of the battery, whilst the non-metal is 
attracted to the (positive) pole connected with the platinum plate of the 
battery. 

Hence the metals are frequently spoken of as electro-positive elements, 
and the non-metals as electro-negative. 

6. If the passage of the " current" be interrupted when the tube H has 
become full of gas, the tube will be only half full, since water contains 
hydrogen and oxygen in the proportion of tivo volumes of hydrogen to one 
volume of oxygen. When the wider portions of the tubes (fig. 1) are 
also filled, the two gases may be distinguished by opening the stop-cocks 
in succession, and presenting a burning match. The hydrogen will be 
known by its kindling with a slight detonation, and burning with a very 
pale flame at the jet; whilst the oxygen will very much increase the 
brilliancy of the burning match, and if a spark left at the extremity of 
the match be presented to the oxygen, the spark will be kindled into a 
flame. 

Another method of effecting the decomposition of water by electricity 
consists in passing a succession of electric sparks through steam. It is 
probable that in this case the decomposition is produced rather by the 
intense heat of the spark than by its electric influence. 

For this purpose, however, the galvanic battery does not suffice, since 
no spark can be passed through any appreciable interval between the wires 
of the battery, — a fact which electricians refer to in the statement that 
although the quantity of electricity developed by the galvanic battery is 
large, its intensity is too low to allow it to discharge itself in sparks like 
the electricity from the machine or from the induction-coil, which pos- 
sesses a very high intensity, though its quantity is small. 

7. The most convenient instrument for producing a succession of elec- 
tric sparks is the induction-coil, by the aid of which the electric influence 

* "YlkeKTpov (amber —root of electricity) ; \vut, to loosen. 



DECOMPOSITION OF STEAM. 7 

of even a single cell of the galvanic battery may be so accumulated as to 
become capable ef discharging itself in sparks, such as are obtained from 
the electrical machine.* 

Fig. 6 represents the arrangement for exhibiting the decomposition of steam by 
the electric spark. 

A is a half-pint flask furnished with a cork in which three holes are bored ; in one 
of these is inserted the bent glass tube B, which dips beneath the surface of the water 
in the trousrh C. 




Fig. 6.— Decomposition of steam by electric sparks. 

D and E are glass tubes, in each of which a platinum wire has been sealed so as 
to project about an inch at both ends of the tube. These tubes are thrust through 
the holes in the cork, and the wires projecting inside the flask are made to approach 
to within about £ s inch, so that the spark may pass easily between them. 

The flask is somewhat more than half filled with water, the cork inserted, and the 
tube B allowed to dip beneath the water in the trough ; the wires in D and E being 
connected with the thin copper wires passing from the induction-coil F, which is 
connected by stout copper wires with the small battery G-. 

The water in the flask is boiled for about fifteen minutes, until all the air con- 
tained in the flask has been displaced by steam. When this is the case, it will be 
found that if a glass test-tube (H) filled with water be invertedf over the orifice of 
the tube B, the bubbles of steam will entirely condense, with the usual sharp rattling- 
sound, and only insignificant bubbles of air will rise to the top of the test-tube. If 
now, whilst the boiling is still continued, the handle of the coil (F) be turned so 
as to cause a succession of sparks to pass through the steam in the flask, large 
bubbles of incondensable gas will accumulate in the tube H. This gas consists of 
the hydrogen and oxygen gases in a mixed state, having been released from their 
combined condition in water by the action of the electric sparks. The gas may be 
tested by closing the mouth of the tube H with the thumb, raising it to an upright 
position, and applying a lighted match, when a sharp detonation will indicate the 
recombination of the gases. X 

It has long been known that a very intense heat is capable of decomposing water. 
The temperature required for the purpose is below the melting point of platinum, as 
may be shown by the apparatus represented in fig. 7. 

A platinum tube (t) is heated by the burner b, the construction of which is shown 
at the bottom of the cut. It consists of a wide brass tube, from which the coal gas 
issues through two rows of holes, between which oxygen is supplied through the holes 
in the narrow tube, brazed into a longitudinal slit between the two rows of holes in 
the gas tube. The oxygen is supplied from a gas-bag or gas-holder, with which the 
pipe (o) is connected. 

The flask (/) containing boiling water is furnished with a perforated cork, carrying 
a brass tube (a), which slips into one end of the platinum tube, into the other end of 

* For a description of the induction-coil, see Miller's "Elements of Chemistry/' Part I. 
p. 575. 

f The end of the tube B should be bent upwards and thrust into a perforated cork with 
notches cut down the sides. By slipping this cork into the neck of the test-tube, the latter 
will be held firmly. 

X With a powerful coil, a cubic inch of explosive gas may be collected in about fifteen 
minutes. 



8 DECOMPOSITION OF STEAM. 

which another brass tube (c) is slipped ; this is prolonged by a glass tube attached by 
india-rubber, so as to deliver the gas under a small jar standing upon a bee-hive shelf 
in the trough. 

The platinum tube is not heated until the whole apparatus is full of steam, and no 



ffc 



« ^A 


I 


^ 








z 


o 








' 


, ^=.-^ 


L#^3 




■■ 



-Decomposition of steam by heat. 



more bubbles of air are seen to rise through the water in the trough ; the gas-burner 
is then lighted, and the oxygen turned on until the platinum tube is heated to a very 
bright red heat ; bubbles of the mixture of hydrogen and oxygen resulting from the 
decomposition of the water may then be collected in the small jar, and afterwards 
exploded by applying a flame. 

8. The decomposition of water by the galvanic current proved that 
there are two volumes of hydrogen combined with one volume of oxygen. 

Hydrogen is the lightest form of matter with which we are acquainted, 
and is therefore generally regarded as the chemical unit of weight and 
volume, i.e., one part by weight of hydrogen occupies one volume. 

Oxygen is found to be sixteen times as heavy as hydrogen, that is, a 
given measure of oxygen weighs sixteen times as much as an equal measure 
of hydrogen. 

Since the two volumes of hydrogen in water represent two parts by 
weight, the one volume of oxygen represents sixteen parts by weight. 

Water is invariably found to contain exactly these proportions of its 
elements, illustrating the low of definite pro-portions ; that a given com- 
pound always contains the same elements in the same proportions. 

This law is characteristic of the force of chemical attraction, no such 
law beiug observed in the operation of either of the other forces of attrac- 
tion by which the particles of matter are influenced, viz., those of gravi- 
tation, cohesion, electricity, and magnetism. To account for the existence 
of such a law limiting the operation of chemical attraction, it is necessary 
to refer to the theory of the atomic constitution of matter. 

Atomic Theory* — All matter is composed of minute particles, which 
are incapable of being further subdivided, and are therefore called atoms, t 

The atoms of the same element have all the same weight, but the atoms 
of different elements have different weights. 

A compound form of matter results from the operation of chemical 
attraction between a definite number of atoms of each of the elements 
composing it. 



Qewpia, a (mode of) viewing. 



t "Ato/jlo's, indivisible. 



ATOMIC THEORY. 9 

Thus, if each atom of oxygen is sixteen times as heavy as each atom of 
hydrogen, water, which contains 16 parts by weight of oxygen, and 2 
parts by weight of hydrogen, must be composed of one atom of oxygen 
and two atoms of hydrogen, as indicated by the formula H 2 0, the atomic 
formula of water. Since it is found that all gases are expanded to the 
same extent by being heated to the same degree, and are contracted to the 
same extent by the application of equal amounts of pressure, they must 
contain equal numbers of atoms in equal volumes.* 

Hence, since water contains twice as many volumes of hydrogen as of 
oxygen, it contains twice as many atoms of hydrogen. 

Very important evidence in favour of the atomic theory is derived from 
the consideration of the specific heats of the elementary forms of matter. 

A given weight of hydrogen gas, in cooling down through one degree 
of the thermometer, gives out sixteen times- as much heat as an equal 
weight of oxygen gas gives out in cooling down through one degree. Or, 
conversely, to raise the temperature of a given weight of hydrogen through 
one degree, requires sixteen times as much heat as would be required to 
raise the temperature of an equal weight of oxygen through one degree. 

This is generally expressed by saying that the specific heat of hydrogen 
is sixteen times that of oxygen. 

Hence, 16 parts by weight of oxygen, in cooling down through one 
degree, gives out as much heat as 1 part by weight of hydrogen. On the 
assumption, therefore, that the atom of oxygen is sixteen times as heavy 
as the atom of hydrogen, the atoms of these elements are associated with 
equal amounts of heat, a conclusion quite in harmony with the results of 
other physical observations. Unfortunately, the specific heats, like the 
specific volumes, of different substances, can only be compared when they 
are in the same physical condition, since the specific heat of a given sub- 
stance varies accordingly as it is in the gaseous, liquid, or solid form, and 
since the greater number of the elements cannot be obtained in the 
gaseous state, it is not possible to compare their specific heats with that 
of hydrogen. Moreover, the determination of the specific heats of gases 
and vapours is attended with great difficulty, so that only oxygen and 
nitrogen have at present been shown by experiment to have the same 
atomic heat as hydrogen. 

(Definition. — The atomic heat of an element is the product of its 
specific heat multiplied by its atomic weight.) 

The atomic heat of hydrogen is 3'4090; those of oxygen and nitrogen 
are 3*48 and 3 - 41 respectively. The atomic heats of the solid elements 
are, as a rule, expressed by a number which is nearly double this, but the 
variations are so considerable (the discrepancy amounting in some cases to 
nearly J^-), that although the identity of the atomic heats is distinctly in- 
dicated, it cannot be said to have been satisfactorily established in all cases. 

9. In the preceding experiments, the force of chemical attraction holding 
the particles of oxygen and hydrogen together in the form of water, has 
been overcome by the physical forces of heat and electricity. But water 
may be more easily decomposed by acting upon it with some element 
which has a sufficiently powerful chemical attraction for the oxygen of 
water to draw it away from the hydrogen. 

No non-metallic element is capable of abstracting the oxygen from water 
at the ordinary temperature. 

* Assuming, of course, £hat the atoms are placed at equal distances apart in the case of 
all 



10 ACTION OF METALS ON WATER. 

Among the practically important metals, there are five which have so 
powerful an attraction for oxygen that it is necessary to preserve them in 
bottles filled with some liquid free from that element, such as petroleum, 
(composed of carbon and hydrogen), to prevent them from combining 
with the oxygen of the atmosphere. These metals are capable of decom- 
posing water with great facility. 

Metals which decompose water at the ordinary temperature. — Potassium, 
Sodium, Barium, Strontium, Calcium. 

When a piece of potassium is thrown upon water, it takes fire and burns 
with a fine violet flame, floating about as a. melted globule upon the surface 
of the water, combining with the oxygen, and producing, in the act of 
combination, enough heat to kindle the hydrogen as it escapes. The 
violet colour of the flame is due to the presence of a little potassium 
in the form of vapour. The same results ensue if the potassium be placed 
on ice. The water in which the potassium has been dissolved will be 
found soapy to the touch and taste, and will have a remarkable action 
upon certain colouring matters. Paper coloured with the yellow dye tur- 
meric becomes brown when dipped in it, and paper coloured with red 
litmus (archil) becomes blue. Substances possessing these properties 
have been known from a very remote period as alkaline substances, ap- 
parently because they were first observed by the alchemists in the ashes 
of plants called kali. 

The alkalies are among the most useful of chemical agents. 

Definition of an alkali. — A compound substance, very soluble in water, 
turning litmus blue and turmeric brown. 

These alkaline properties are directly opposed to the characters of 
sour or acid* substances, such as vinegar or vitriol, which change the 
blue litmus to red. 

When an acid liquid, such as vinegar (acetic acid) or vitriol (sulphuric 
acid), is added to an alkaline liquid, the characteristic properties of the 
latter are destroyed, the alkali being neutralised. 

An acid substance may be known by its property of neutralising an 
alkali (either entirely or partly). 

The minute investigation into the action of potassium upon water 
would require considerable manipulative skill. It would be necessary to 
Aveigh accurately the potassium employed, to evaporate the resulting 
solution in a silver basin (most other materials being corroded by the 
alkali), and after all the water had been expelled by heat, to ascertain the 
composition of the residue by a chemical analysis. 

It would be found to contain, by weight, 1 part of hydrogen, 16 parts 
of oxygen, and 39 parts of potassium. 

Since water contains 2 parts by weight of hydrogen, combined with 
16 parts of oxygen, it is evident that the product of the action of potas- 
sium on water is formed by the substitution of 39 parts of potassium for 
1 part of hydrogen. 

It is found that whenever potassium takes the place of hydrogen in a 
compound, 39 parts of the former are exchanged for one of the latter, and 
this is generally expressed by stating that 39 is the chemical equivalent 
of potassium. 

The chemical equivalent of a metal expresses the weight which is 
required to be substituted for one part by weight of hydrogen in its 
compounds. 

* From «m;, a point, referring to the pungency or sharpness of the acid taste. 



ACTION OF METALS ON WATER. 



11 



The action of potassium upon water is an example of the production of 
compounds by substitution of one element for another, a mode of forma- 
tion which is far more common than the production of compounds by 
direct combination of their elements. 

It is commonly assumed by chemists that the weight of an atom of 
potassium is 39 times that of an atom of hydrogen. 

If the symbol K be taken to represent 39 parts by weight of potassium, 
its action upon water would be represented by the chemical equation 



H,0 + 

Water. 



K = KHO + H 

Caustic potash.* 



Sodium has a less powerful attraction for oxygen than potassium, and 
does not usually take fire when thrown into cold water, although it is at 
once fused by the heat evolved in its combination with the oxygen. By 
holding a lighted match over the globule as it swims upon the water, the 
hydrogen may be kindled, when 
its flame is bright yellow from the 
presence of the sodium. The solu- 
tion will be found strongly alkaline 
from the soda produced. By plac- 
ing the sodium on a piece of blotting- 
paper laid on the water, it may be 
made to ignite the hydrogen spon- 
taneously, because the paper keeps 
it stationary, and prevents it from 
being so rapidly cooled by the water. 
Several cubic inches of hydrogen 
may easily be collected by placing 
a piece of sodium as large as a bean 
in a small wire-gauze box (A, fig. 8), and holding it under an inverted 
cylinder (B) filled with water and standing upon a bee-hive shelf. 

The product of the action of sodium upon water contains 1 part by 
weight of hydrogen, 16 of oxygen, and 23 of sodium, so that the 23 parts 
of sodium have been exchanged for, or been found chemically equivalent 
to, 1 part of hydrogen. 

The atom of sodium is generally taken to be twenty-three times as heavy 
as the atom of hydrogen. 

Taking the symbol Na to represent 23 parts by weight of sodium, its 
action on water would be expressed thus — 




H 2 



Na 



= ]S T aHO + H 

Caustic soda. 



Barium, strontium, and calcium decompose water less rapidly than 
potassium and sodium. 

The tendency of heat to separate the elements of water being known, 
it might be expected that metals which refuse to decompose water at the 
ordinary temperature, would be induced to do so if the temperature were 
raised, and accordingly magnesium and manganese, which are without 
action upon cold water, decompose it at the boiling point, disengaging 
hydrogen, and producing magnesia (MgO, a feebly alkaline earth) and 
oxide of manganese (MnO). 

* Caustic, from Kcu<a, to "burn, in allusion to its corrosive properties ; and potash, from 
its having been originally prepared from the washings of wood ashes boiled down in iron 
pots and decomposed by lime. 



12 



ACTION OF METALS ON WATER. 



But the greater number of the common metals must be raised to a much 
higher temperature than this in order to enable them to decompose water. 
The following metals will abstract the oxygen from water at high tem- 
peratures, those at the commencement of the list requiring to be heated 
to redness (about 1000° F.), and the temperature required progressively 
increasing, until it attains whiteness for those at the end of the list. 

Metals which decompose water at a temperature above a red heat. — 
Zinc, Iron, Chromium, Cobalt, Nickel, Tin, Antimony, Aluminum, Lead, 
Bismuth, Copper. 

The noble metals, as they are called, which exhibit no tendency to 
oxidise in air, are incapable of removing the oxygen from water, even 
at high temperatures. 

Metals which are incapable of decomposing luater. — Mercury, Silver, 
Gold, Platinum. 



HYDROGEN. 

10. Preparation of hydrogen. — The simplest process, chemically speak- 
ing, for preparing hydrogen in quantity, consists in passing steam over 
red-hot iron. An iron tube (A, fig. 9) is filled with iron nails and fixed 




F.g. D. -Preparation ofhy 



ii iruiii steam 



across a furnace (B), in which it is heated to redness by a charcoal fire. 
A current of steam is then passed through it by boiling the water in the 
flask (C), which is connected with the iron tube by a glass tube (D) and 
perforated corks. The hydrogen is collected from the glass tube (G) in 
cylinders (E) filled with water, and inverted in the trough (F) upon the 
bee-hive shelf (H), the first portions being allowed to escape, as containing 
the air in the apparatus. The iron combines with the oxygen of the 
water to form the black oxide of iron (Fe,0 4 ), which will be found in 
a crystalline state upon the surface of the metal. The decomposition is 
represented by the equation 



4H 2 

Water. 



F< 



= Fe A + 

Black oxide of iron. 



II 



PREPARATION OF HYDROGEN. 



13 



The weight of an atom of iron is believed to be 56 times that of an atom 
of hydrogen; hence the Fe 3 in the above equation represent 56 x 3, or 
168 parts by weight of iron. 

The process by which hydrogen is most commonly prepared consists in 
dissolving iron or zinc in a mixture of sulphuric acid and water. 

Zinc is the most conve- 
nient metal to employ for the 
preparation of hydrogen in 
this way. It is used either in 
small fragments or cuttings, 
or as granulated zinc, pre- 
pared by melting it in a ladle 
and pouring it from a height 
of three or four feet into a 
pailful of water. The zinc 
is placed in the bottle 
(A, fig. 10), covered with 
water to the depth of two 
or three inches, and diluted 
sulphuric acid slowly poured 
in through the funnel tube 
(B) until a pretty brisk effervescence is observed. The hydrogen is unable 
to escape through the funnel tube, since the end of it is beneath the surface 
of the water, but it passes off through the bent tube (C), and is collected 
over water as usual, the first portion being rejected as containing air. 

By evaporating the larger excess of water from the solution left in the 
bottle, crystals of sulphate of zinc (white vitriol) may be obtained. 

It will be noticed that the liquid becomes very hot during the action 
of the acid upon the zinc, the heat being produced by the combination 
which is taking place. The black flakes which separate during the solu- 
tion of the zinc consist of metallic lead, which is always present in the 
zinc of commerce, and much accelerates the evolution of hydrogen by 
causing galvanic action. Pure zinc placed in contact with diluted sulphuric 
acid evolves hydrogen very slowly. 

The preparation of hydrogen by dissolving zinc in diluted sulphuric acid 
may be represented by the equation* 




Fig. 10. — Preparation of hydrogen. 



H 2 O.S0 3 + 

Sulphuric acid 
combined with water. 



Zn = ZnO . SG 3 + H 2 

Sulphate of zinc. 



The symbol Zn here represents one atom of zinc, which is believed to 
be 65 times as heavy as the atom of hydrogen. An atom of zinc has 
here displaced two atoms of hydrogen, whereas it was found that an atom 
of potassium displaced only one atom of hydrogen, that is, 39 parts by 
weight of potassium are equivalent to 1 part of hydrogen. 

The atomic weight and equivalent weight of potassium, therefore, are 
represented by the same number, which is often expressed by saying that 
potassium is a monatomic element, i.e., is exchangeable for one atom of 
hydrogen. 

* In this equation the excess of water which must he added to dissolve the sulphate of 
zinc is not set down. Hydrogen could not he prepared according to the equation as it 
stands, because the sulphate of zinc would collect round the metal and prevent further 
action. 



14 PROPERTIES OF HYDROGEN. 

But since 65 parts of zinc displace 2 parts of hydrogen, the equivalent 
of zinc, or that quantity which is exchangeable for 1 part by weight of 
hydrogen, would be 32*5. 

The atomic weight of zinc, therefore, is double its equivalent weight, 
or zinc is a diatomic element, i.e., is exchangeable for two atoms of 
hydrogen. This is commonly expressed by writing the symbol of zinc 
thus— Zn". 

Iron might be used instead of zinc, and the solution when evaporated 
would then deposit crystals of green vitriol or copperas (sulphate of iron 
FeO . S0 3 ), the action of iron upon water in the presence of sulphuric 
acid being represented by the equation 

H 2 . SO, + Fe = FeO . S0 3 + H 2 

Sulphuric acid c , . , . 

combined with water. Sulphate of iron. 

which shows that one atom (56) of iron has taken the place of two atoms 
of hydrogen. 28 would then be the chemical equivalent of iron, and this 
metal is diatomic, like zinc. 

11. Physical properties of hydrogen. — This gas is permanent, invisible, 
and inodorous when pure. The hydrogen obtained by the ordinary 
methods has a very disagreeable smell, caused by the presence of minute 
quantities of compounds of hydrogen with sulphur, arsenic, and carbon ; 
but the gas prepared with pure zinc and sulphuric acid is quite free from 
smell. The most remarkable physical property of hydrogen is its light- 
ness. It is the lightest of all kinds of matter, being about ^ as heavy 
as air, and ytiq2 a §: heavy as water. 

The lightness of hydrogen may be demonstrated by many interesting experiments. 
Soap bubbles or small balloons (of collodion for example) will ascend very rapidly if 
inflated with hydrogen. A light beaker glass may be accurately weighed in a pair 
of scales ; it may then be held with its mouth downwards, and hydrogen poured up 
into it from another vessel. If it be then replaced upon the scale-pan with its 
mouth downwards, it will be found very much lighter than before. Another form 
of the experiment is represented in fig. ]1, where a light glass shade has been sus- 
pended from the balance and counterpoised, the equilibrium being, of course, at once 
disturbed when hydrogen is poured up into the shade. If a stoppered gas jar full 
of hydrogen be held with its mouth downwards, and a piece of smouldering brown 
paper held under it, the smoke, which would rise freely in the air, is quite unable 
to rise through the hydrogen, and remains at the mouth of the jar until the stopper 
is removed, when the hydrogen quickly rises and the smoke follows it. 

12. The employment of hydrogen for filling balloons renders a know- 
ledge of the relation between the weights of equal volumes of hydrogen 
and atmospheric air of great importance. The number expressing this 
relation is termed the specific gravity of hydrogen. 

Definition. — The specific gravity of a gas or vapour is its weight as 
compared with that of an equal volume of some other gas, selected as a . 
standard, at the same temperature and pressure. 

If the weight of a given volume of purified and dried air be repre- 
sented as unity, an equal volume of hydrogen, at the same temperature 
and pressure, would weigh 0*0692, which is expressed by saying that the 
specific gravity of hydrogen (air = 1) is 0*0692. In ascertaining the 
weights of definite volumes of gases, it is of the greatest importance that 
they should have some definite temperature and pressure, since the volume 
of a given weight of gas is augmented by increase of temperature and by 



DIFFUSION OF GASES. 



15 



decrease in pressure. In England it is usual to state the weights of gases 
at the temperature of 60° on the Fahrenheit thermometer, and under a 
pressure of 30 inches of mercury in the barometer, these being regarded 
as the average conditions of the climate. 




Fig. 11. 



On the Continent the standard pressure is very nearly the same, beiug 
760 millimetres of the barometric column, or 29*922 inches; but the 
standard temperature is that of melting ice, or 0° on the centigrade 
scale, corresponding to 32° F., a temperature to which gases may be reduced 
at will, by surrounding with melting ice the vessels in which they are 
collected for the purpose of being weighed. 

One grain of hydrogen, at 60° F. and 30 inches Bar., measures 46*73 
cubic inches. 

Expressed on the Continental system, one gramme (15 "43 grains) of 
hydrogen, at 0° C. and 760 mm. Ear., measures 11*19 litres (one litre = 
61*024 cubic inches = 1*76 pints). 

It is now easy to calculate how much zinc it would be necessary to dissolve in 
sulphuric acid in order to obtain any desired volume, say 100 cubic feet (172,800 
cubic inches) of hydrogen. Referring to the equation for the preparation of hydro- 
gen, Zn + H 2 . S0 3 = H 2 + ZnO . SO s , and remembering that Zn represents 65 
parts by weight of zinc, and H 2 2 parts by weight of hydrogen — 



2 grs. H. 
"46 cub. in. 



grs. Zn. 
: 65 



Cub. in. 
172800 



x(= 12018 grs. zinc). 



13. It will be observed, in the experiment with the balance (fig. 11), 
that the gas gradually falls out of the jar, notwithstanding its lightness, 
and is replaced by air; so that, after a time, the equilibrium is re- 
stored. This is accounted for by a physical property belonging to 
all gases (and vapours) called diffusibility, which may be defined as 
the tendency of the particles of a gas to separate as far as possible from 
each other. If a jar of hydrogen were placed with its mouth down- 
wards over a jar of air, this mutual repulsion among the particles of each 



16 DIFFUSION OF GASES. 

gas would cause it to diffuse itself equally throughout both jars, so that, 
eventually, as much hydrogen will be found in the lower jar as if it had 
been completely exhausted of air before the commencement of the experi- 
ment. This is often expressed by the statement that one gas acts as a 
vacuum to another, which is true as far as the ultimate result is con- 
cerned, though, of course, the time occupied by the passage of a gas into 
a vacuum would be far less than that required for its passage into another 
gas. Even if the two jars be connected only by a tube with the narrowest 
passage possible, the same result would be arrived at, but after a longer 
period. 

This tendency of the particles of a gas to separate as far as possible from each other, 
or as it is sometimes called, the 'mutual repulsion of the particles of gases, is due to the 
constant movement of these particles ; for although no appearance of motion can be 
seen, a little consideration will show that the particles of a gas are never at rest. It 
is well known that in a vessel containing a gas, the pressure of the gas is exerted 
equally in all directions upon the sides of the vessel ; and if two vessels be filled with 
gases of different relative weights, the pressure may be the same in both, notwith- 
standing the difference in the actual weights of the gases. For example, if two jars 
of equal size be filled with hydrogen and oxygen, over the pneumatic trough, the 
pressure of each gas will equal that of the atmosphere, when the water within the 
jars has the same level as the water in the trough, although the actual weight of the 
oxygen is sixteen times that of the hydrogen . 

The pressure of the gas upon the sides of the containing vessel is due to the con- 
stant motion of its particles, which causes them to strike upon the sides of the vessel 
with an amount of force which constitutes the pressure. Thus, in a gas having a 
pressure equal to that of the atmosphere, the particles of gas are delivering blows 
upon the sides of the containing vessel with a force amounting to about 15 lbs. 
upon every square inch of the surface. Since each particle of hydrogen is only -^ of 
the weight of the particle of oxygen, it is evident that, in order to strike the sides of 
the vessel with the same force, the velocity of the hydrogen particles must be much 
greater than that of the oxygen particles. But if the hydrogen particles moved six- 
teen times as rapidly as the oxygen particles; not only would each hydrogen particle 
strike sixteen blows whilst each oxygen particle was striking one blow, but sixteen 
times as many hydrogen particles would deliver their blows in the same time, and 
we should have — 

Weight. Velocity. fftSSbST P — 

Oxygen, 16 x 1 x 1 =16 

Hydrogen, 1 x 16 x 16 16 x 16. 

If, however, the hydrogen particles move with four times the velocity of the oxygen 
particles, the pressures of the gases will be equal, thus — 

No. of strokes P re ssnr P 

in same time. pressure. 

x 1 =16 

x 4 =16. 

This affords an illustration of the law that the rates of diffusion of the gases are 
inversely as the square roots of their relative weights. 

Rate of Diffusion . Rate of Diffusion . . - _ , ._ 
of Hydrogen, of Oxygen, ' * Vl6 : v 1 . 

It has been calculated that the actual velocity or rate of translation of the particles 
of hydrogen amounts to 6050 feet per second. 

"When a jar of hydrogen, having its mouth turned upwards, is open to the air, the 
rapid escape of the hydrogen is due, firstly, to its displacement, in consequence of 
the heavier air falling into the jar, and, secondly, to the rapid motion or diffusion 
of the particles of the hydrogen, which projects them out of the mouth of the vessel. 
It is found that the escape due to the first of these causes may be prevented by clos- 





Weight. 


Velocity 


Oxygen, 
Hydrogen, 


16 

1 


x 1 
x 4 



DIFFUSION OF GASES. 



17 




Fiff. 12. 



ing tlie moutli of the vessel with a plate of dry plaster of Paris, or of certain other 
materials having very minute pores; but this does not prevent the escape of the 
hydrogen by diffusion, and therefore permits the rate of diffusion to be measured. 

The diffusion tube (fig. 12) employed for this purpose 
is a glass tube (A) closed at one end by a plate of plaster 
of Paris (B). If this tube be filled with hydrogen,* and 
its open end immersed in coloured water, the water will 
be observed to rise rapidly in the tube, on account of the 
rapid escape of the hydrogen through the pores of the 
plaster. The external air, of course, passes into the tube 
through the pores at the same time, but much less rapidly 
than the hydrogen passes out, so that the ascent of the 
column of water (C) marks the difference between the 
volume of hydrogen which passes out, and that of air 
which passes into the tube in a given time, and allows a 
measurement to be made of the rate of diffusion; that is, 
of the velocity with which the gas issues on account of 
the repulsion among its particles, as compared with the 
velocity with which the air enters, this velocity being 
always taken as unity. f To determine the rate of diffu- 
sion, it is of course necessary to maintain the water at the 
same level within and without the diffusion tube, so as to 
exclude the influence of pressure. 

To prove that the ascent of the hydrogen due to its lightness is not instrumental 
in drawing up the water in the diffusion tube, the experiment may be made as in 
fig. 13, where the plate of plaster (o) is turned, downwards, so that the diffusion is 
made to take place in opposition to the action of 
gravity. This tube is filled by passing hydrogen in 
through the tube (s), and allowing the air to escape 
through (t), which is afterwards closed by a cork. 
The plaster of Paris (o) is tied over with caoutchouc 
whilst the tube is filled. 

Since the relation between the weights of equal 
volumes of hydrogen and air is that of 0*069 : 
1, the rates of diffusion will be as 1 : VO'069 — 
that is, hydrogen will diffuse about 3 '8 times as 
rapidly as atmospheric air, or 3*8 measures of hydro- 
gen will pass out of the diffusion tube whilst one 
measure of air is passing in through the plaster. In a 
similar manner hydrogen would escape through 
minute openings with nearly four times the velocity 
of oxygen ; and laboratory experience shows that a 
cracked jar, or a bottle with a badly fitting stopper, 
may often be used to retain oxygen, but not hydrogen. 

A. very striking illustration of the high rate of diffusion of hydrogen is arranged 
as represented in fig. 14. A is a cylinder of porous earthenware (such as are 
employed in galvanic batteries) closed at one end, and furnished at the other 
with a perforated bung, through which passes a glass tube B, about three feet long, 
and half an inch in diameter. The bung is made air-tight by coating it with sealing 
wax dissolved in spirit of wine. This tube being supported so that its lower end 
dips about an inch below the surface of water, a jar of hydrogen is held over the 
porous cylinder, when the self-repulsion of the particles of the gas is manifested by 
their being forced (not only out of the mouth of the jar C, which is open at the 
bottom, but also) through the pores of the earthenware jar, the air from which is 
violently driven out, as if by blowing, through the tube, and is seen bubbling up 
rapidly through the water. When the air has ceased to bubble out, and a large 
volume of hydrogen has entered the porous jar, the bell -jar C is removed, when the 
hydrogen escapes so rapidly through the pores, that a column of twenty or thirty 
inches of water is drawn rapidly up the tube B. If the greatest height to which the 
water ascends be marked, and when it has returned to its former level, a jar of coal- 

* This tube must be filled by displacement (see fig. 18), in order not to wet the plaster. 
A piece of sheet caoutchouc may be tied over the plaster of Paris, so that diffusion may 
not commence until it is removed. 

t Air being a mixture of nitrogen and oxygen, its rate of diffusion is intermediate 
between the rates of those gases ; however, since the proportions of the gases are very 
nearly constant, no error of any magnitude arises. 




Diffusion tube. 



18 



PROPERTIES OF HYDROGEN. 




gas be held over the porous cylinder, it will be found that the above phenomena 
are manifested in a much lower degree, showing that coal-gas, being heavier than 

hydrogen, does not pass nearly so rapidly through 
the pores of the earthenware as hydrogen does. 

The great difference in the rates of diffusion of 
hydrogen and oxygen may be easily shown by the 
arrangement represented in fig. 15. A, is a jar 
filled with a mixture of two volumes of oxygen 
with one volume of hydrogen, communicating 
through the stop-cock and flexible tube with the 
glass tube B, which is fitted through a perforated 
cork in the. bowl of the common tobacco pipe C, 
the sealing- waxed end of which dips under water 
in the trough D. By opening the stop-cock and 
pressing the jar down in the water, the mixed 
gases may be forced rapidly through the pipe, and 
if a small cylinder (E) be filled with them, the 
mixture will be found to detonate violently 
on the approach of a flame. But if the gas be 
made to pass very slowly through the pipe (at 
the rate of about a cubic inch per minute), the 
hydrogen will diffuse through the pores of the 
pipe so much faster than the oxygen, that the gas 
collected in the cylinder will contain so little 
hydrogen as to be no longer explosive, and to 
exhibit the property of oxygen to rekindle a 
partly extinguished match. 

If two jars of the same size, one made of glass, 
and the other of porous earthenware, be filled with 
the explosive mixture by holding them over the 
stop-cock of the jar A, and be then closed with 
glass plates and set aside for a few seconds, it will 
be found that the gas in the earthen jar will re- 
kindle a spark on a match, whilst that in the 
glass jar will explode. 

14. Chemical properties of hydrogen. — 
The most conspicuous chemical property of 
hydrogen is its disposition to burn in air 
when raised to a moderately high tempera- 
ture, entering into combination with the 
oxygen of the air to form water. The 
formation of water during the combustion of 
hydrogen gave rise to its name (vSoyp, water). 

On introducing a taper into an inverted jar of hydrogen (fig. 16), the flame of the 
taper will be extinguished, but the hydrogen will burn with a pale flame at the mouth 
of the jar, and the taper may be rekindled at its flame by slowly withdrawing it. 

The lightness and combustibility of hydrogen may be illustrated simultaneously 
by some interesting experiments. If two equal gas cylinders be filled with hydrogen, 
and held with their mouths respectively upwards and downwards, it will be found, 
on testing each with a taper after the same interval, that the hydrogen has entirely 
escaped from the cylinder held with its mouth upwards, whilst the other still remains 
nearly filled with the gas. 

The hydrogen may be scooped out of the jar A (fig. 17). with the small cylinder B . 
attached to a handle. On removing B, and applying a taper to it, the gas will take fire. 

A cylinder may be filled with hydrogen by displacement of air (fig. 18), if the tube 
from the hydrogen bottle be passed up into it. 

If such a dry cylinder of hydrogen be kindled whilst held with its mouth down- 
wards, the formation of water during the combustion of the hydrogen will be indi- 
cated, by the deposition of dew upon the sides of the cylinder. 

By softening a piece of glass tube in the flame of a spirit-lamp, drawing it out 
and filing it across in the narrowest part (fig. 19), a jet can be made from which 
the hydrogen may be burnt. This jet may be fitted by a perforated cork to any 
common bottle for containing the zinc and sulphuric acid (fig. 20). 




Fig. 14, 



PROPERTIES OF HYDROGEN, 



19 



The hydrogen must be allowed to escape for some minutes before applying a light, 
because it forms an explosive mixture with the air contained in the bottle. This 




~— 7 »w/<y ~»am 

Fig. 15. — Separation of hydrogen and oxygen by atmolysis.* 

may be proved, without risk, by placing a little granulated zinc in a soda-water 
bottle, pouring upon it some diluted sulphuric acid, and quickly inserting a perforated 






Fig. 18. 



Fig. 17. 



Fiff. 18. 



cork, carrying a piece of glass tube about three inches long, and one-eighth of an inch 
wide. If this tube be immediately applied to a flame, the mixture of air and hydro- 
gen will explode, and the cork and 
tube will be projected to a consi- 
derable distance. 

By inverting a small test-tube 
over the jet in fig. 20, a specimen 
of the hydrogen may be collected, 
and may be kindled, to see if it 
burns quietly, before lighting the jet, 

* This term has been applied to the separation of gases by diffusion ; £tuos, vapour- 
kvw, to loosen. 




Fig. 19. 



20 



EXPLOSION OF HYDROGEN AND AIR. 



A dry glass, held over the flame, will collect a considerable quantity of water, 
formed by the combustion of the hydrogen. 

The combustion of hydrogen produces a greater heating effect than that 
of an equal weight of any other combustible body. It has been deter- 
mined that 1 gr. of hydrogen, in the act of combining with 8 grs. of 
oxygen, produces enough heat to raise 62,031 grs. of water from 32° F. 
to 33° F. (or 34,462 grs. from 0° C. to 1° C.) The temperature of the 
hydrogen name is higher than that of any other single flame with which 
we are acquainted. Notwithstanding its high temperature, the flame of 
hydrogen is almost devoid of illuminating power, on account of the 
absence of solid particles. 

15. If a taper be held several inches above a cylinder of hydrogen, 
standing with its mouth upwards, the gas will be kindled with a loud 
explosion, because an explosive mixture of hydrogen and air is formed in 
and around the mouth of the cylinder. 





Fig. 20. 

If a stoppered gas jar (fig. 21) be filled with hydrogen, and supported upon three 
blocks, it will be found, if the hydrogen be kindled at the neck of the jar, that it will 
burn quietly until air has entered from below in sufficient proportion to form an 
explosive mixture, which will then explode with a loud report. 

The same experiment may be tried on a smaller scale, with the two-necked copper 
vessel (fig. 22), the lower aperture being opened some few 
seconds after the hydrogen has been kindled at the upper 
one. 

The explosion of the mixture of hydrogen and 
air is due to the sudden expansion caused by the 
heat generated in the combination of the hydrogen 
with the oxygen throughout the mixture. After 
the explosion of the mixture of hydrogen and air 
(oxygen and nitrogen), the substances present are 
steam (resulting from the combination of the hydro- 
gen and oxygen) and nitrogen,- which are expanded 
by the heat developed in the combination to a 
volume far greater than the vessel can contain, so that a portion of the 
gas and vapour issues very suddenly into the air around, the collision 
with which produces the report. 

If pure oxygen be substituted for air, the explosion will be more violent, 
because the mixture is not diluted with the inactive nitrogen. The 
further study of this subject must be preceded by that of oxygen. 




Fig. 22. 



PROPERTIES OF OXYGEN. 21 



OXYGEN. 

0= 16 parts by weight = 1 vol. 16 grs. = 467 cub. in. at 60° F. and 30" Bar. 
16 grammes = 11 *2 litres at 0° C. and 760 mm. Bar. 

1 6. Oxygen is the most abundant of the elementary substances. It con- 
stitutes about one-fifth (by volume) of atmospheric air, where it is merely 
mixed, not combined, with the nitrogen, which composes the bulk of the 
remainder. Water contains eight-ninths (by weight) of oxygen ; whilst 
silica and alumina, which compose the greater part of the solid earth (as 
far as we know it), contain about half their weight of oxygen. 

Before inquiring which of these sources will most conveniently furnish 
pure oxygen, it will be desirable for the student to acquire some know- 
ledge of the properties of this element, and of the chemical relations 
which it bears to other elementary bodies, for without such knowledge it 
will be found very difficult to understand the processes by which oxygen 
is procured. 

17. Physical properties of Oxygen. — From the fact of its occurring in an 
uncombined state in the atmosphere, it will be inferred that oxygen is 
perfectly invisible, and without odour. It is a permanent gas, having 
resisted all attempts to reduce it to a liquid or solid state. Oxygen is a 
little more than one- tenth heavier than air, which is expressed in the 
statement that its specific gravity is 1*1057. 

In the study of theoretical chemistry, it is expedient to select hydro- 
gen instead of air as the standard with which the specific gravities of 
gases are compared ; for since the atomic weights are also referred to 
hydrogen as the unit, and the atomic weights represent the weights of 
equal volumes, the members expressing the atomic weights of the ele- 
mentary gases are identical with their specific gravities (H = I). Thus, 
the specific gravity of oxygen (H = I) is 16. It will be found con- 
venient to remember that the specific gravity of a gas or vapour is the 
iveight of one volume. 

18. Chemical properties of Oxygen. — This element is remarkable for the 
wide range of its chemical attraction for other elementary bodies, with all 
of which, except one, it is capable of entering into combination. Fluorine 
is the only element which is not known to unite with oxygen. 

With nearly all the elements oxygen combines in a direct manner ; 
that is, without the intervention of any third substance. 

There are only seven elements (among those of practical importance) 
■which do not unite in a direct manner with oxygen, viz., chlorine, bromine, 
iodine, fluorine, gold, silver, platinum. 

(Definition. — The compounds of oxygen with other elements are called 
Oxides.) 

The act of combination with oxygen, or oxidation, like all other acts of 
chemical combination, is attended with the development of heat.* When 
the heat thus produced is sufficient to render the particles of matter 
luminous, the act of combination is styled combustion. 

* Though this heat is not always perceptible by the thermometer or by the senses. 
Thus, when chalk is dissolved in an acid, no heat is perceived, because all the heat attend- 
ing the union of the lime with the acid is consumed in converting the carbonic acid from 
the solid chalk into a gas. To explain the manifestation of heat in the act of chemi- 
cal combination falls within the province of the physicist rather than of the chemist. 
Modern writers attribute it to the motion of the molecules which compose the combining 
masses. 



22 



COMBUSTION. 



(Definition.- 
and light.) 



■Combustion is chemical combination attended with heat 



(Definition.— Combustion 



19. Phosphorus, the only non-metal ivhich combines with oxygen at the 
ordinary temperature, affords a good illustration of these propositions. 
This element, a solid at the ordinary temperature, is preserved in bottles 
filled with water, on account of the readiness with which the oxygen of 
the air combines with it. If a small piece of phosphorus be dried by 
gentle pressure between blotting paper, and exposed to the air, its par- 
ticles begin to combine at once with oxygen, and the heat thus developed 
slightly raises the temperature of the mass. 

Now, heat generally encourages chemical union, so that the effect of 
this rise of temperature is to induce a more extensive combination of the 
phosphorus with the oxygen, causing a greater development of heat in a 
given time, until the temperature is sufficient to render the particles 
brilliantly luminous, and a true case of combustion results — the combina- 
tion of the phosphorus with oxygen, attended with production of heat 
and light. 

air is the chemical combination of the 
elements of the combustible with the 
oxygen of the air, attended with de- 
velopment of heat and light.) 

If a dry glass (fig. 23) be placed over 
the burning phosphorus, the thick 
white smoke which proceeds from it 
may be collected in the form of snowy 
flakes. These flakes are commonly 
termed anhydrous phosphoric acid* 
and are composed of 80 parts by 
weight of oxygen, and 62 parts of 
phosphorus (P 2 O s ). 
11 the white flakes are exposed to the air for a short time, they attract 
moisture and become little drops, which have a very sour or acid taste. 
It was mentioned at page 10 that all substances which have such a taste 
have been found also to be capable of changing the blue colour of litmus f 
to red, whence the chemist is in the habit of employing paper dyed with 
blue litmus for the recognition of an acid. It must be remembered, how- 
ever, that there are some acids which, not being dissolved by water, have 
neither a sour taste nor the power of reddening litmus, so that, in exact 
research, another mode of defining the acid character of a substance is 
employed. Ordinary sand is known to chemists as silicic acid, but, of 
course, does not answer to either of the above tests. 
JFor the exact definition of an acid see page 25. 

During the slow combination of phosphorus with the oxygen of the air, 
before actual combustion commences, only 48 parts of oxygen unite with 
62 parts of phosphorus, forming the substance called anhydrous phos- 
phorous acid (P 2 O.J. 

(Definition. — The endings -ous and -ic distinguish between two com- 
pounds formed by oxygen with the same element; -ous implying the 
smaller proportion of oxygen.) 

* Anhydrous, or without water, from av, negative, and vomp, water, 
t A colouring matter, prepared from a lichen, Roccella tinctorw ; the cause of the 
change of colour will be more easily understood hereafter. 




OXYGEN. 



23 



Unless the temperature of the air be rather high, the fragment of phos- 
phorus will not take fire spontaneously, hut its combustion may always 
be ensured by exposing a larger surface to the action of the air. As a 
general rule, a fine state of division favours chemical combination, because 
the attractive force inducing combination operates only between sub- 
stances in actual contact ; and the smaller the size of the particles, the 
more completely will this condition be fulfilled. 

Thus, if a small fragment of dry phosphorus be placed in a test-tube, and dis- 
solved in a little bisulphide of carbon, the solution, when poured upon blotting paper 
(fig. 24), will part with the solvent by 
evaporation, leaving the phosphorus in a 
very finely divided state upon the surface 
of the paper, where it is so rapidly acted 
on by the oxygen of the air that it bursts 
spontaneously into a blaze. 

Though the light emitted by phos- 
phorus burning in air is very bril- 
liant, it is greatly increased when 
pure oxygen is employed ; for since the nitrogen with which the oxygen 
in air is mixed takes no part in the act of combustion, it impedes and 
moderates the action of the oxygen. Each volume of the latter gas is 
mixed, in air, with four volumes of nitrogen, so that we may suppose five 
times as many particles of oxygen to come into contact, in a given time, 
with the particles of the phosphorus immersed in the pure gas, which 
will account for the great augmentation of the temperature and light of 
the burning mass. 

To demonstrate the brilliant combustion of phosphorus in oxygen, a piece not 
larger than a good-sized pea is placed in a little copper or iron cup upon an iron 
stand (fig. 25), and kindled by being touched 
with a hot wire (for even in pure oxygen spon- 
taneous combustion cannot be ensured). The 
globe, having been previously filled with oxy- 
gen, and kept in a plate containing a little 
water, is placed over the burning phosphorus .* 




Fig. 24. 




Pig. 25. — Phosphorus burning in 
oxygen. 



It will be observed that the same white 
clouds of phosphoric acid are formed, 
whether phosphorus is burnt in oxygen 
or in air, exemplifying the fact that a 
substance will combine loith the same pro- 
portion of oxygen, ivhether its combustion 
be effected in pure oxygen or in atmospheric air. The apparent increase 
of heat is due to the combustion of a greater weight of phosphorus in a 
given time and space. The total heating effect produced by the combus 
tion of a given weight of phosphorus is the same whether air or pure 
oxygen be employed. 

20. Sulphur (brimstone) affords an example of a non-metallic element 
which will not enter into combination with oxygen until its temperature 
has been raised very considerably. When sulphur is heated in air, it 
soon melts ; and as soon as its temperature reaches 500° F. it takes fire, 
burning with a pale blue flame. If the burning sulphur be plunged into 
a jar of oxygen, the blue light will become very brilliant, but the same 

* This globe should be of thin, well-annealed glass, and is sure to be broken if too 
large a piece of phosphorus be employed. 



24 



OXYGEN WITH NON-METALS. 




Fig. 26. — Sulphur burning in 
oxygen. 



act of combination takes place — 32 parts by weight of oxygen uniting 
with 32 parts of sulphur to form sulphurous acid gas (S0 2 ), which may 
be recognised in the jar by the well-known suffocating smell of brimstone 
matches. 

The experiment is most conveniently performed by heating the sulphur 
in a deflagrating spoon (A, fig. 26), which is then plunged into the jar of 

oxygen, its collar (B) resting upon the 
neck of the jar, which stands in a plate 
containing a little water. The water ab- 
sorbs a part of the sulphurous acid gas, 
and will be found capable of strongly red- 
dening litmus paper. It is possible to 
produce, though not by simple combus- 
tion, a compound of sulphur with half as 
much more oxygen (S0 3 , anhydrous sul- 
phuric acid), showing that a substance does 
not alioays take up its full share of oxygen 
ivhen burnt. 

The luminosity of the flame of sulphur 
is far inferior to that of phosphorus, be- 
cause, in the former case, there are no 
minute solid particles in the flame corresponding to those of the phos- 
phoric acid produced in the combustion of phosphorus, and no flame 
can emit a brilliant light unless it contains solid matter heated to incan- 
descence. 

21. Carbon, also a non-metallic element, requires the application of a 
higher temperature than sulphur to induce it to enter into direct union 
with oxygen ; indeed, perfectly pure carbon appears to require a heat 
approaching whiteness to produce this effect. But charcoal (the carbon 
in which is associated with not inconsiderable proportions of hydrogen 
and oxygen) begins to burn in air at a much lower temperature ; and if a 
piece of wood charcoal, with a single spot heated to redness, be lowered 
into a jar of oxygen, the adjacent particles will soon be raised to the 
combining temperature, and the whole mass will glow intensely, 32 parts 
by weight of oxygen uniting with 1 2 parts of carbon to form carbonic 
acid (C0 2 ) gas, which will redden a piece of moistened blue litmus paper 
suspended in the jar, though much more feebly than either sulphurous or 
phosphoric acid, because it is a much weaker acid. It should be remem- 
bered that carbon is an essential constituent of all ordinary fuel, and car- 
bonic acid is always produced by its combustion. 

It will be noticed that the combustion of the charcoal is scarcely at- 
tended with name; and when pure carbon (diamond, for example) is 
employed, no flame whatever is produced in its combustion, because car- 
bon is not convertible into vapour, and all flame is vapour or gas in the 
act of combustion ; hence, only those substances burn with flame which are 
capable of yielding combustible gases or vapours. 

22. The three examples of sulphur, phosphorus, and carbon suffi- 
ciently illustrate the tendency of non-metals to form acids by union with 
oxygen, which originally led to the adojDtion of its name, derived from 
6£vs acid, and yei/raw, I produce. All the non-metallic elements, except 
hydrogen and fluorine, are capable of forming acids by their union with 
oxygen. 



OXYGEN WITH METALS. 25 

The circumstance that only those acids which can be dissolved by- 
water have any action upon litmus, and that some of these have a very 
feeble effect, renders it necessary to fix some other criterion by which an 
acid may be invariably recognised. Such a criterion is found in the 
original idea of an acid, as a substance neutralising an alkali. In the 
case of some acids, such as sulphuric, it is easy to exhibit the neutralising 
power ; but with others, such as carbonic and silicic, it is not so easy to 
ascertain that neutralisation has taken place, because the alkali is only 
partly neutralised. In practice, therefore, the following definition will 
be found more convenient : — 

Definition of an Acid. — A compound body lohich evolves water by its 
action upon pure caustic potash or soda. 

For example — 

2 KHO + C0 2 =■ K 2 O.C0 2 + H 2 

Caustic potash. Carbonic acid. Carbonate of potash. Water. 

^aHO + HC1 = ^aCl + H 2 . 

Caustic soda. Hydrochloric acid. Common salt. Water. 

23. The metals, as a class, exhibit a greater disposition to unite directly 
with oxygen, though few of them will do so in their ordinary condition, 
and at the ordinary temperature. Several metals, such as iron and lead, 
are superficially oxidised when exposed to air under ordinary conditions, 
but this would not be the case unless the air contained water and car- 
bonic acid, which favour the oxidation in a very decided manner. Among 
the metals which are of importance in practice, five only are oxidised by 
exposure to dry air at the ordinary temperature, viz., potassium, sodium, 
barium, strontium, and calcium, the attraction of these metals for oxygen 
being so powerful that they must be kept under petroleum, or some 
similar liquid free from oxygen. On the other hand, three of the com- 
mon metals, silver, gold, and platinum, have so little attraction for 
oxygen that they cannot be induced to unite with it directly, even at 
high temperatures. 

If a lump of sodium be cut across with a knife, the fresh surfaces will 
exhibit a splendid lustre, but will very speedily tarnish by combining 
with oxygen from the air, which gives rise to a coating of oxide of sodium 
or soda, and this to some extent protects the metal beneath from oxida- 
tion. The freshly cut sodium shines, in the dark, like phosphorus. Even 
when the attraction of the sodium for oxygen is increased by the appli- 
cation of heat, it is long before the mass of sodium is oxidised through- 
out, unless the temperature be sufficiently high to convert a portion of the 
sodium into vapour, which bursts through the crust of soda, and burns 
with a yellow flame. If the spoon containing the sodium (see fig. 26) be 
now plunged into a jar of oxygen, the yellow flame will be far more bril- 
liant. 

Sixteen parts by weight of oxygen here combine with 46 parts of sodium 
to form soda (Na 2 0), which remains in the spoon in a fused state. "When 
the spoon is cool, it may be placed in water, which will dissolve the soda, 
converting it into caustic 



Xa 2 + H 2 = 2K"aHO. 

Soda. Water. Caustic soda. 



24. Zinc will serve as an example of a metal which has no disposition 



26 



OXYGEN WITH METALS. 




Fig. 27. — Zinc burning in oxygen. 



to enter into combination with oxygen at the ordinary temperature,* but 
which is induced to unite with it by a very moderate heat. If a little 
zinc (spelter) be melted in a ladle or crucible, and stirred about with an 
iron rod, it burns with a beautiful greenish flame produced by the union 

of the vapour of zinc with the oxygen of 
the air. But the combustion is far more 
brilliant if a piece of zinc-foil be made 
into a tassel (fig. 27), gently warmed at 
the end, dipped into a little flowers of 
sulphur, kindled, and let down into ajar 
of oxygen, when the flame of the burning 
sulphur will ignite the zinc, which burns 
with great brilliancy. On withdrawing 
what remains of the tassel after the com- 
bustion is over, it will be found to con- 
sist of a friable t mass, which has a fine 
yellow colour while hot, and becomes white as it cools. This is the oxide 
of zinc (ZnO), formed by the union of 16 parts by weight of oxygen with 
65 parts of zinc. 

The oxide of zinc does not possess the properties of an acid or an alkali, 
but belongs to another class of compounds termed bases, which are not 
soluble in water as the alkalies are, but, like them, are capable of neutral- 
ising, either partly or entirely, the acids. Thus, if the oxide of zinc were 
added to diluted sulphuric acid as long as the acid would dissolve it, the 
well-known corrosive properties of the acid would be destroyed, although 
it would still retain the power of reddening blue litmus, and the solution 
would now contain a new substance, or salt, called sulphate of zinc 
(ZnO.S0 3 ). 

(Definition. — A base is a compound body which is capable of neutral- 
ising an acid, either partly or entirely.) 

It will be observed that an alkali is only a particular species of base, 
and might be defined as a base which is very soluble in water. 

(Definition. — A salt is a compound body containing an acid in com- 
bination with a base, or a metal in combination with a salt-radical. % 
Examples. — Carbonate of, soda (Na 2 O.C0 2 ), composed of carbonic acid 
(C0 2 ) and soda (Na 2 0) ; Chloride of sodium (JSTaCl), composed of the metal 
sodium and the salt-radical chlorine.) 

(Definition. — A salt-radical or halogen is a substance which forms an 
acid when combined with hydrogen. Examples. — Chlorine, which forms 
hydrochloric acid (HC1) ; Cyanogen (CN), which forms hydrocyanic acid 

(HCN).) 

25. Iron, in its ordinary form, like zinc, is not oxidised by dry air or 

oxygen at the ordinary temperature • but if it be heated even to only 
500° F. a film of oxide of iron forms upon its surface, and as the heat is 
increased the thickness of the film increases, until eventually it becomes so 
thick that it can be detached by hammering the surface, as may be seen 
in a smith's forge. If an iron rod as thick as the little finger be heated 
to whiteness at the extremity, and held before the nozzle of a powerful 
bellows, it will burn brilliantly, throwing off sparks and dropping melted 

* Unless water and carbonic acid be present, as in common air. 
t Friable, easily crumbled or disintegrated. 

J Salts of this description are termed haloid sails, because they belong to the same class 
as sea-salt (NaCl), from d\<s, the sea. 



OXIDES. 



27 




Fig. 28. 



-Watch-spring burning 
in oxygen. 



oxide of iron. If a stream of oxygen be substituted for air, the 
combustion is of the most brilliant description. A watch-spring (iron 
combined with about 1 per cent, of carbon) 
may be easily made to burn in oxygen by 
heating it in a flame till its elasticity is 
destroyed, and coiling it into a spiral (A, 
fig. 28), one end of which is fixed, by 
means of a cork, in the deflagrating collar B ; 
if the other end be filed thin and clean, 
dipped into a little sulphur, kindled, and 
immersed in a jar of oxygen (C) standing 
in a plate of water, the burning sulphur 
will raise the iron to the point of com- 
bustion, and the spring will be converted 
into molten drops of oxide. 

The black oxide of iron formed in all these cases is really a com- 
bination of two distinct oxides of iron, one of which contains 16 parts by 
weight of oxygen and 56 parts of iron, and would be written FeO, whilst 
the other contains 48 parts of oxygen and 112 parts of iron, expressed by 
the formula Fe 2 3 . To distinguish them, the former is usually called 
protoxide of iron (7rpwros, first), and the latter sesquioxide (in allusion to 
the ratio of one and a half to one between the oxygen and the metal).* 
The sesquioxide of iron combined with water constitutes ordinary rust. 

The black oxide usually contains one combining weight of each oxide, 
so that it would be written FeO.Fe 2 Oo, or Fe 3 4 . It is powerfully 
attracted by the magnet, and is often called magnetic oxide of iron. The 
abundant magnetic ore of iron, of which the loadstone is a variety, has a 
similar composition. 

Iron in a very fine state of division will take fire spontaneously in air 
as certainly as phosphorus. Pyroplioric iron can be obtained (by a process 
to be described hereafter) as a black powder, which must be preserved in 
sealed tubes. When the tube is opened, and its contents thrown into the 
air, oxidation takes place, and is attended with a vivid glow. In this 
case the red sesquioxide of iron is produced instead of the black oxide. 

Both these oxides of iron are capable of neutralising, or partially neu- 
tralising, acids, and are therefore basic oxides or bases, like the oxides of 
zinc and sodium obtained in previous experiments. So general is the 
disposition of metals to form oxides of this class, that it may be regarded 
as one of the distinguishing features of a metal, for no non-metal ever 
forms a base with oxygen. 

(Definition. — A metal is an element capable of forming a baset by 
combining with oxygen, or salt by combining with a salt-radical.) 

Many metals are capable also of forming acids with oxygen ; thus, tin 
forms stannic acid (SnO.,), antimony forms antimonic acid (Sb..0 5 ), and 
it is always found that the acid oxide of a metal contains a larger pro- 
portion of oxygen than any of the other oxides which the metal may 
happen to form. 

26. There is a third class of oxides, termed the indifferent oxides, be- 
cause they are neither acids nor bases ; such oxides may be formed either 

* The terms ferrous and ferric oxide are now very often substituted for protoxide and 
sesquioxide of iron. 

t The metal tungsten appears at present to be an exception to this rule, no well- 
defined basic oxide of this metal being known. 



28 PREPARATION OF OXYGEN. 

by non-metals or metals ; thus water (H 2 0), the oxide of hydrogen, is an 
indifferent oxide, and the black oxide or binoxide of manganese (Mn0 2 ) 
is an example of an indifferent metallic oxide. 

27. Preparation of Oxygen. — For almost all the useful arts in which 
uncombined oxygen is required, the diluted gas contained in atmospheric 
air is sufficient, since the nitrogen mixed with it does not interfere with 
its action. 

From atmospheric air pure oxygen was first obtained by Lavoisier towards 
the end of the last century. His process is far too tedious to be employed 
as a general method of preparing oxygen, but it affords a very good example 
of the relation of heat to chemical attraction. Some mercury was poured 
into a glass flask with a long narrow neck, which was placed in a sand- 
bath, so that its temperature might be constantly maintained at about 
660° F. for several weeks. The mercury boiled, and a portion of it was 
converted into vapour, which condensed in the neck of the flask and ran 
back again. Eventually the mercury was converted into a red powder, 
having combined with the oxygen of the air (or undergone oxidation) to 
form the red oxide of mercury. The nitrogen of the air does not enter 
into combination with the mercury. 

Ey heating this oxide of mercury to a temperature approaching a red 
heat (about 1000° F.) it is decomposed into mercury and oxygen gas 
(HgO = Hg + 0). 

It is very generally found, as in this instance, that heat of moderate 
intensity will favour the operation of chemical attraction, whilst a more 
intense heat will annul it. 

For the purpose of experimental demonstration, the decomposition of the oxide 
of mercury may be conveniently effected in the apparatus represented by fig. 29, 
where the oxide is placed in the German glass tube A, and heated by the Bunsen's 




Fig. 29. — Preparation of oxygen from oxide of mercury. 

gas-burner B, the metallic mercury being condensed in the bend C, and the oxygen 
gas collected in the gas cylinder D. filled with water, and standing upon the bee- 
hive shelf of the pneumatic trough E. It may be identified by its property of kindling 
into flame the spark left at the end of a wooden match. If the heat be continued 
for a sufficient length of time, the whole of the oxide of mercury will disappear, 
being resolved into its elements. In technical language, the mercury is said to be 
vccLii cocL 

Upon the first application of heat, the red oxide suffers a physical change, in 
consequence of which it becomes black ; but its red colour returns again if it be 
allowed to cool. 

A much cheaper process for obtaining unmixed oxygen from the air is 
now employed upon the large scale. It depends upon the principle that 
the oxides of manganese, when heated in contact with alkalies and air, 



EXTRACTION OF OXYGEN FROM AIR. 



29 



are capable of absorbing the oxygen from the air, and of subsequently 
giving it up again if heated in a current of steam. 

To illustrate this process, about four ounces of dry manganate of soda (which may 
be purchased cheaply in a crude state) are introduced into a porcelain tube (t, fig. 30) 
fixed in a furnace. One end of the tube is connected with a two branched glass tube, so 
that either a current of air may be paased through it by the tube a, or a current of 
steam from the flask w. On heating the manganate of soda in the tube to dull red- 
ness, and passing the steam over it, oxygen is evolved, and may be collected in the 
jar o. 

2Na„Mn0 4 + 2H 2 = 4NaHO + Mn 2 3 + 8 . 

Manjfanate of Caustic soda Sesquioxide ot 

soda. Caustic soda. mangaiiese . 

If the current of steam be discontinued, and air be slowly passed through the 
tube a, the oxygen of the air will be absorbed, and its nitrogen may be collected in 
the jar n. 



4NaHO + Mn 2 0, + 



3(0 + N 4 ) 

Air. 



2Ka MnO A + 2PLO + N, 



If the proper temperature be employed, the stream of gas issuing from the tube 
may be constantly kept up, and may be made to consist of oxygen or nitrogen 
accordingly as steam or air is passed through the tube. The current of air is regu- 
lated by the nipper-tap c. 

The gas-furnace represented in fig. 30 consists of a row of twelve Bunsen burners, 
each having a stop-cock by which the flame is regulated. The horizontal pipe b, 
from which they spring, is capable of being raised or lowered at pleasure. The 
porcelain tube t is laid in a semi-cylindrical trough made of stout iron rods, and 
filled with pieces of pumice-stone or fire-brick. Above this is placed a corresponding 
trough, so that the tube is entirely surrounded by glowing material.* The heat 
must be applied gradually to avoid splitting the tube. 




Fig. 30 —Extraction of oxygen from air. 

28. The only other natural source from which it has been found con- 
venient to prepare pure oxygen is a black mineral composed of manganese 
and oxygen. It is found in some parts of England, but much more 
abundantly in Germany and Spain, whence it is imported for the use of 
the bleacher and glass-maker. Its commercial name is manganese, but it 

* This burner, as well as the burner described at page 8, was constructed for me by Mr 
Rowley, of the Royal Military Academy, Woolwich, whose readiness in perceiving the 
intention of an apparatus, and in improving upon the original idea as the work proceeds, 
renders his co-operation in arranging experimental illustrations of the greatest service 
to me. 



30 



PEEPAEATION OF OXYGEN. 



is known to chemists as binoxlde of manganese (MnO.,), and to minera- 
logists by several names designating different varieties. The most signi- 
ficant of these names is pyrol/usite, referring to the facility with which it 
may be decomposed by heat (irvp, fire, and Auw, to loosen). 

One of the cheapest methods of preparing oxygen consists in heating 
small fragments of this black oxide of manganese in an iron retort, placed 
in a good fire, the gas being collected in jars filled with water, and stand- 
ing upon the shelf of the pneumatic trough, or in a gas-holder or gas-bag, 
if larger quantities are required. 

The attraction existing between manganese and oxygen is too powerful 
to allow the metal to part with, the whole of its oxygen when heated, so 
that only one-third of the oxygen is given off in the form of gas, a brown 
oxide of manganese being left in the retort. * 

29. By far the most convenient source of oxygen, for general use in the 
laboratory, is the artificial salt called chlorate of potash, which is largely 

manufactured for fireworks, percussion- 
cap composition, &c. If a few crystals 
of this salt be heated in a test-tube over 
a spirit-lamp (fig. 31), it soon melts to a 
clear liquid, which, presently begins to 
boil from the disengagement of bubbles 
of oxygen, easily recognised by intro- 
ducing a match, with a spark at the end 
into the upper part of the tube. If the 
action of heat be continued until no more 
oxygen is given off, the residue in the 
tube will be the salt termed chloride of 
potassium, f 




Fig. 31. 



' KC10 S 

Chlorate of potash. 



KC1 4 

Chloride of potassium. 



0, 



To ascertain what quantity of oxygen would lie furnished by a given weight of 
chlorate of potash, the combining weights must be brought into use. Referring to 
the table of atomic weights, it is found that K = 89, = 16, and CI = 35*5 
hence the molecular weight of chlorate of potash is easily calculated. 

One atomic weight of potassium, . 39 » 

,, ,, chlorine, . . 35*5 

Three atomic weights of oxygen, . . 48 

KC10 3 = 122-5 

So that 122' 5 grains of chlorate of potash would yield 48 grains of oxygen. 

Since 16 grs. of oxygen measure 46*7 cubic inches (p. 21), the 48 grs. will measure 
140 cubic inches. 

Hence it is found that 122*5 grains of chlorate of potash would give 140 cub. in. 
of oxygen measured at 60° F. and 30 in Bar. 

If one gallon (277 "276 cub. in.) of oxygen be required, 242 '6 grains of chlorate of 
potash must be used, or rather more than half an ounce. 

Since the complete decomposition of the chlorate of potash alone re- 
quires a more intense heat than a glass vessel will usually endure, it is 
customary in preparing oxygen for chemical purposes to facilitate the 

Mn 3 4 + 2 . 
Brown oxide of 
manganese. manganese. 

t The oxygen contained in the chlorate of potash was derived from the lime employed 
in its manufacture (see Preparation of Chlorate of Potash). Its original source, therefore, 
was limestone. 



Expressed in the form of an equation : 3Mn0 2 

Black oxide of 



WATEE. 



31 



decomposition of the chlorate by mixing it with about one-fifth of its 
weight of powdered black oxide of manganese, when the whole of the 
oxygen is given off at a comparatively low temperature, though the oxide 
of manganese itself suffers no change, and its action has not yet received 
any explanation which is quite satisfactory. 

Fig. 32 shows a very convenient arrangement for preparing and collecting oxygen 
for the purpose of demonstrating its relations to combustion. A is a Florence flask, 




Fig. 32. — Preparation of oxygen. 

in which the glass tube B is fixed by a perforated cork. C is a tube of vulcanised 
india-rubber. The gas-jar is filled with water, and supported upon a bee-hive shelf 
made of earthenware. If pint gas-jars be employed, 300 grains of the chlorate of 
potash, mixed with 60 grains of binoxide of manganese, will furnish a sufficient sup- 
ply of gas for the ordinary experiments. The binoxide of manganese should be 
thoroughly dried by moderately heating it in a crucible before being mixed with the 
chlorate of potash. It is also advisable to test it by heating a little of it with the 
chlorate, since charcoal and sulphuret of antimony, which form very explosive mix- 
tures with chlorate of potash, have sometimes been sold by mistake for binoxide of 
manganese. The heat must be moderated according to the rate at which the gas is 
evolved, and the tube C must be taken out of the water before the lamp is removed, 
or the contraction of the gas in cooling will suck the water back into the flask. The 
first jar of gas will contain the air with which the flask was filled at the commence- 
ment of the experiment. The oxygen obtained will have a slight smell of chlorine. 



WATEE. 



30. Synthesis of Water from its elements. — It has been seen already 
(p. 20) that the combination of hydrogen with oxygen to form water is 
attended with great evolution of heat and consequent expansion, and 
hence the mixture of these gases is found to explode violently on contact 
with flame. 

The experiment may be made safely in a soda-water bottle. The bottle is filled 
with water, and inverted with its mouth beneath the surface of the water ; enough 
oxygen is then passed up into it to fill one-third of its volume ; if the remainder of 
the water be then displaced by hydrogen, and the mouth of the bottle be presented 
to the flame of a spirit-lamp, a very violent explosion will result, attended with a 
vivid blue flash in the bottle. If the mouth of the bottle be presented towards a 
screen of paper, at a distance of 20 or 30 inches, the paper will be violently torn to 
pieces, bearing witness to the concussion between the expanded steam issuing from 
the bottle, and the external air. 

If some of the mixture of oxygen, with twice its volume of hydrogen, be introduced 
into a capped jar (fig. 33), provided with a piece of caoutchouc tubing and a small 
glass tube, and pressed down in a trough of water, soap-bubbles may be inflated with 



32 



SYNTHESIS OF WATER. 



it, which will ascend rapidly in the air, and explode violently when touched with a 
flame, which must not, of course, he applied to the bubble until it is at some distance 
away from the tube, for fear of exploding the mixture in the jar. 

31. In order to demonstrate the production of water in the explosion, the Caven- 
dish eudiometer* (fig. 34) is employed. This is a strong glass vessel, with a stopper 




Fig. 33. 

firmly secured by a clamp (A), and provided with two platinum wires (P), which pass 
through the stopper, and approach very near to each other within the eudiometer, so 
that the electric spark may easily be passed between them. By screwing the stop- 
cock B into the plate of an air-pump, the eudiometer may be exhausted. It is then 
screwed on to the jar represented in fig. 35, which contains a mixture of two measures 





Fig. 34. 

of hydrogen with one measure of oxygen, standing over water. On opening the stop- 
cocks between the two vessels, the eudiometer becomes filled with the mixture, and 
the quantity which has entered is indicated by the rise of the water in the jar. The 
glass stop-clock C having been closed, to prevent the brass cap from being forced off 
by the explosion, the eudiometer is again screwed on to its foot, and an electric spark 
passed between the platinum wires, either from a Leyden jar or an induction coil, 
when the two gases will combine with a vivid flash of light, t attended with a very 

* So named from tvSio-z, fine or clear, and ixerpov, a measure, because an instrument 
upon the same principle has been used to determine the degree of purity of the atmosphere. 
The eudiometer was employed by Cavendish about the year 1770, for the synthesis of 

t Since the steam produced at the moment of combination is here prevented from 
expanding the heat which would have expanded it is saved, so that the temperature is 
higher and the flash of light brighter than when the combination is effected in an open 
vessel. 



EUDIOMETPJC ANALYSIS OF AIR. 



33 



slight concussion, since there is no collision with the external air. For an instant 
a mist is perceived within the eudiometer, which condenses into fine drops of dew, con- 
sisting of the water formed by the combination of the gases, which was here induced 
by the high temperature of the electric spark, as it was in the former experiment by 
the high temperature of the flame. If the gases have been mixed in the exact pro 
portion of two measures of hydrogen to one measure of oxygen, the eudiometer will 
now be again vacuous, and if it be screwed on to the capped jar, may be filled a second 
time with the mixture, which may be exploded in the same manner. 

The entire disappearance of the gases may be rendered obvious to the eye by 
exploding the mixture over mercury. For this purpose the mixed gases should be 
collected from water itself, which is strongly acidified with sulphuric acid, and 
decomposed in the voltameter (A, fig, 36) by the nid of five or six cells of Grove's 
battery. The voltameter contains two platinum plates (B), attached to the platinum 




Fig. 36 — Detonating gas collected from voltameter. 

wires (J and D, which are connected with the opposite poles of the battery. The 
first few bubbles of the mixture of hydrogen and oxygen evolved having been allowed 
to escape, in order to displace the air, the gas may be collected in the small eudio- 
meter (E), which has been previously filled with water. This eudiometer is a cylinder 
of very thick glass,* closed at one end, and having two stout platinum wires cemented 
into holes drilled near the closed end, the wires approaching sufficiently near to each 
other to allow the passage of the electric spark. Having been filled with the mixture 
of hydrogen and oxygen from the voltameter, the eudiometer is closed with the finger, 
and transferred to a basin containing mercury, where it is pressed firmly down upon 
a stout cushion of india-rubber, and the spark passed through the mixed gases, 
either from the coil or the Leyden jar. The combustion takes place with violent 
concussion, but without noise ; and since the eudiometer is vacuous after the gases 
have combined, the cushion will be found to be very firmly pressed against its open 
end. On loosening the cushion, the mercury will be violently forced up into the 
eudiometer, which will be completely filled with it, proving that when an electric 
spark is passed through the mixture of two volumes of hydrogen and one volume of 
oxygen, no residue of gas remains.t 

32. The knowledge of the volumes in which hydrogen and oxygen 
combine, is turned to account in the analysis of gases, to ascertain the 
proportion of hydrogen or oxygen contained in them. Suppose, for 
example, it he required to determine the amount of oxygen in a sample 
of atmospheric air ; the latter is mixed with hydrogen, in more than suffi- 
cient quantity to combine with the largest proportion of oxygen which 

* The bore of this eudiometer should be about half an inch in diameter, and the thick- 
ness of its sides about three-eighths of an inch ; its length is 7 inches. 

t This fact may also be demonstrated with the siphon eudiometer, shown in fig. 37, by 
confining about a cubic inch of the explosive mixture in the closed limb, over water, and 
stopping the open limb securely with a cork, so as to leave a space filled with air between 
the cork and the water. The eudiometer must be very firmly fixed on a stand, or it will 
be broken by the concussion. After it has been proved, it may be held in the hand, as 
in the figure. By firing mixtures of hydrogen and oxygen, in different proportions, in the 
same manner, it may be shown that any excess of either gas above the ratio of 2H : 10 will 
remain uncombined after the explosion. Care is required in these experiments, since 
eudiometers are often burst by the explosion of the mixture of 2 vols, of hydrogen with 
1 vol. of oxygen. 

C 



34 



EUDIOMETRIC ANALYSIS OF AIR. 



could be present, and when the combination has been induced by the 
electric spark, the volume of gas which has disappeared (2 vols. H + 1 
vol. 0) has only to be divided by three to give the volume of the oxygen. 

A bent eudiometer (fig. 37) is generally employed for tins purpose. Having been 
completely filled with water, it is inverted in the trough, and the specimen of air is 
introduced (say 0'5 cubic inch). The open limb is then closed by the thumb, and 
the eudiometer turned so as to transfer the air to the closed 
limb. A stout glass rod is thrust down the open limb, so as 
to displace enough water to equalise the level in both limbs, 
in order that the volume of the air may not be diminished 
by the pressure of a higher column of water in the open limb. 
The volume of the included air having been accurately 
noted, the open limb of the tube is again filled up with 
water, inverted in the trough, and a quantity of hydrogen 
introduced, equal to about half the volume of the air. This 
having been transferred, as before, to the closed limb, the 
columns of water are again equalised, and the volume of the 
mixture of air and hydrogen ascertained. The open limb is 
now firmly closed with the thumb, and the electric spark 
passed through the mixture, either from the Leyden jar or 
the induction coil. On removing the thumb, after the 
explosion, the volume of gas in the closed limb will be found to have diminished 
very considerably. Enough water is poured into the open limb to equalise the level, 
and the volume of gas is observed. If this volume be subtracted from the volume 
before explosion, the volume of gas which has disappeared will be ascertained, and 
one-third of this will represent the oxygen, which has condensed with twice its volume 
of hydrogen into the form of water. Thus the numbers recorded will be — 




Fig. 37. 
Siphon eudiometer. 



Volume of air analysed, 

Volume of air mixed with hydrogen, 
After explosion, 



Difference, 
(§ H and } 0) 

■30, divided by 3 



0*50 cub. in. 

0*75 
0-45 



•30 



•10 cub. 



of 



oxygen. 



It is evident that the volume of hydrogen contained in a gas might be 
ascertained in a similar manner, by exploding with oxygen, and taking 
two-thirds of the gas which had disappeared in the form of water to 
represent the volume of hydrogen. 

In exact experiments, a correction would be required for any variation of 
the temperature or barometric pressure during the progress of the analysis. 

33. It will have been observed, in the experiment upon the synthesis 
of water in the Cavendish eudiometer, that the volume of water obtained 
is very small in comparison with that of the gases before combination, 
nearly 2600 volumes of the mixed gases being required to form one volume 
of the liquid. But it is evident that no comparison can, with propriety, 
be made between the volume of a compound, in the liquid or solid state, 
and that of its components in the gaseous state, since the particles of i 
the former are under the influence of the cohesive force from which those 
of the latter are free. For the purposes of such a comparison the volume 
of the compound body must be taken under precisely the same physical 
conditions as the volume of its components. 

If the mixture of hydrogen and oxygen be measured and exploded at 
a temperature above the boiling point of water, it is found that the steam 
produced occupies two-thirds of the volume of the mixed gases, measured 
at the same temperature and atmospheric pressure. Hence, two volumes 



WATER OF WELLS, SPRINGS, AND RIVERS. 



43 




nature of the soils and rocks which it has touched, and attaining its 
highest point in sea water, which contains a larger proportion of saline 
matters than water from any other natural source. Ice, when melted, 
affords nearly pure water, since, when water containing salts is partially 
frozen, these are left dissolved in the uncongealed water. 

If a quantity of rain, spring, river, or sea water be boiled in a flask 
furnished with a tube also filled with the water, and passing under a gas 
cylinder standing in a trough 
of the same water (fig. 44), 
it will be found to give off a 
quantity of gas which was 
previously held in solution 
by the water, and is now set 
free because gases are less 
soluble in hot than in cold 
water. The quantity of this 
gas will vary according to 
the source of the water, but 
it will always be found to 
contain the gases existing in 
atmospheric air, viz., nitro- 
gen, oxygen, and carbonic 

acid. One gallon of rain Fig. 44. 

water will generally furnish 

about 4 cubic inches of nitrogen, 2 cubic inches of oxygen, and 1 cubic 
inch of carbonic acid. It is worthy of remark, that the nitrogen and 
oxygen have been dissolved by the water, not in the proportions in which 
they exist in the atmosphere (4 1ST : 1 0), but in the proportions in which 
they ought to be dissolved, if it be true that they exist in the air in the 
condition of mere mechanical admixture. The oxygen thus carried down 
from the air by rain appears to be serviceable in maintaining the respira- 
tion of aquatic animals, and in conferring upon river waters a self-purify- 
ing power, by acting upon certain organic matters which would probably 
prove hurtful to animals, and converting them into harmless products of 
oxidation. In the cases of rivers contaminated with the sewage of towns, 
this action of the dissolved oxygen is probably of great importance. 
The carbonic acid dissolved in rain water also probably serves some 
useful purposes in the chemical economy of Nature. (See Carbonic 
Acid.) 

43. The waters of wells, springs, and rivers, and especially those of 
the two first-named sources, differ very much from each other, according 
to the nature of the layers of rock or earth over or through which they 
have passed, and from which they dissolve a great variety of substances, 
some of which are familiar to us in daily life, while others are only met 
with in chemical collections. Under' the former head may be enume- 
rated Glauber's salt (sulphate of soda), common salt (chloride of sodium), 
Epsom salt (sulphate of magnesia), gypsum (sulphate of lime), chalk 
(carbonate of lime), common magnesia (carbonate of magnesia), carbonic 
acid, and silica. 

Among the substances known only to the chemist, may be mentioned 
sulphuretted hydrogen, sulphate of potash, chloride of potassium, chloride 
of calcium, chloride of magnesium, phosphate of lime, bromides and 



44 HARD WATERS. 

iodides of calcium and magnesium (rarely), alumina (probably sulphate 
of alumina), carbonate of iron, and certain vegetable substances.* 

The well waters of certain localities (as, for example, those of large 
towns) also frequently contain salts of nitric and nitrous acids, and of 
ammonia. 

The waters of springs and rivers do not differ very materially from 
well waters as to the nature of the substances which they contain, though, 
in the case of river waters more particularly, the quantity of these sub- 
stances is materially influenced by the conditions of rapid motion and 
exposure to air under which such waters are placed. 

Household experience has established a classification of the waters 
from natural sources into soft and hard waters — a division which depends 
chiefly upon the manner in which they act upon soap. If a piece of 
soap be gently rubbed in soft water (rain water, for example) it speedily 
furnishes a froth or lather, and its cleansing powers can be readily 
brought into action ; but if a hard water (spring water) be substituted for 
rain water, the soap must be rubbed for a much longer time before a 
lather can be produced, or its effect in cleansing rendered evident ; a 
number of white curdy flakes also make their appearance in the hard 
water, which were not seen when soft water was used. The explanation 
of this difference is a purely chemical one. 

Soap is formed by the combination of a fatty acid with an alkali ; it is 
manufactured by boiling oil or fat with potash or soda, the former for 
soft, the latter for hard soaps. In the preparation of ordinary hard soap, 
the soda takes from the oil or fat two acids, — stearic and oleic acids, — 
which exist in abundance in most varieties of fat, and unites with them 
to form soap, which in chemical language would be spoken of as a mix- 
ture of st ear ate and oleate of soda. 

If soap be rubbed in soft water until a little of it has dissolved, and 
some Epsom salts (sulphate of magnesia) be dissolved in water, and 
poured into the soap water, curdy flakes will be produced, as when soap 
is rubbed in hard water, and the soap water will lose its property of froth- 
ing when stirred ; the sulphate of magnesia has decomposed the soap, the 
soda contained in the latter has combined with the sulphuric acid exist- 
ing in the sulphate of magnesia, to form a sulphate of soda which remains 
dissolved in the water, while the magnesia, uniting with the stearic and 
oleic acids, produces the insoluble curdy flakes, which consist of stearate 
and oleate of magnesia. 

Similar to the effect of the sulphate of magnesia is that of hard waters; 
their hardness is attributable to the presence of the different salts of lime 
and magnesia, all of which decompose the soap in the manner exempli- 
fied above ; the peculiar properties of the soap in forming a lather and 
dissolving grease can, therefore, be manifested only when a sufficient 
quantity has been employed to decompose the whole of the salts of lime 
and magnesia contained in the quantity of water operated on, and thus a 
considerable amount of soap must be rendered useless when hard water is 
employed. 

On examining the interior of a kettle in which spring, well, or river 
water has been boiled, it will be found to be coated more or less thickly 
with a fur or incrustation, generally of a brown colour, and the harder 

* Although it is certainly known that the acids and bases capable of forming the salts 
here enumerated may be detected in spring and river waters, their exact distribution 
amongst each other is still a matter of uncertainty. 



INCRUSTATIONS ON BOILERS. 45 

the water, the more speedily will this incrustation be deposited. A 
chemical examination shows this deposit to consist chiefly of carbonate of 
lime, in the form of minute crystals, which may be discovered by the 
microscope ; it usually contains, in addition, some carbonate of magnesia, 
sulphate of lime, and small quantities of sesquioxide of iron, (rust), and 
vegetable matter, the last two substances imparting its brown colour. In 
order to explain the formation of this deposit, it is necessary to become 
acquainted with the particular condition in which the carbonate of lime 
exists in natural waters. Carbonate of lime is hardly dissolved to any 
perceptible extent by pure water, though it may be dissolved in con- 
siderable quantity by carbonic acid. This statement, which is of great 
importance in connection with natural waters, may be verified in the 
following manner. A little slaked lime is well shaken up in a bottle of 
distilled or rain water, which is afterwards set aside for an hour or two ; 
as soon as that portion of the lime which has not been dissolved has sub- 
sided, the clear portion is carefully poured into a glass, and a little soda- 
water or solution of carbonic acid in water is added to it ; the first addi- 
tion of the carbonic acid to the lime water causes a milkiness, due to the 
formation of minute particles of carbonate of lime, by the union of the 
carbonic acid with the lime ; this carbonate of lime, being insoluble in 
the water, separates from it, or precipitates and impairs the transparency 
of the liquid ; a further addition of carbonic acid water renders the liquid 
again transparent, for the carbonic acid dissolves the carbonate of lime 
which has separated, forming, in the opinion of some chemists, a definite 
chemical compound, the bicarbonate of lime, which contains twice as 
much carbonic acid as the carbonate ; since, however, this bicarbonate of 
lime has not been separated from the water in a pure state, it is safer to 
regard it merely as a solution of carbonate of lime in free carbonic acid. 

If this clear solution be introduced into a flask, and boiled over the 
spirit-lamp or gas-flame, it will again become turbid, for the free carbonic 
acid will be expelled by the heat, and the carbonate of lime will be de- 
posited, not now, however, in so fine a powder as before, but in small 
hard grains which have a tendency to fix themselves firmly upon the 
sides of the flask, and, when examined by the -microscope, are seen to 
consist of small crystals. 

In a similar manner, when natural waters are boiled, the free carbonic 
acid which they contain is expelled in the gaseous state, and the carbon- 
ates of lime, magnesia, and oxide of iron are precipitated, since they are 
insoluble in water which does not contain carbonic acid. But, by the 
ebullition of the water, a portion of it has been dissipated in vapour, and 
if there be much sulphate of lime present, the quantity of water left may 
not be sufficient to retain the whole of that salt in solution ; and this is 
the more likely to happen, because sulphate of lime requires about 400 
parts of water to dissolve it ; * a quantity of sulphate of lime, then, is 
liable to be deposited together with the carbonates of lime, magnesia, and 
oxide of iron, and, should the water contain much vegetable matter, this 
is also often deposited in an insoluble condition, the whole eventually 
forming together a hard compact mass, composed of successive thin layers, 
on the bottom and sides of the vessel in which the water has been boiled. 

* Sulphate of lime has been found nearly insoluble in water having a higher temperature 
than 212° F., as would be the case in boilers worked under pressure, so that it would 
readily be deposited. It is said that waters containing little or no sulphate of lime yield 
a loose and friable deposit. 



46 CALCAREOUS WATERS. 

The "furring" of a kettle is objectionable, chiefly in consequence of its 
retarding the ebullition of the water, since the deposit is a very bad con- 
ductor of heat, and therefore impedes the transmission of heat from the 
fire to the water; hence the common practice of introducing a round stone 
or marble into the kettle, in order, by its perpetual rolling, to prevent the 
particles of carbonate of lime from forming a compact layer. In steam 
boilers, however, even more serious inconvenience than loss of time some- 
times arises if this deposit be allowed to accumulate, a"nd to form a 
thick layer of badly conducting material on the bottom of the boiler, since 
the latter is then liable to become red hot, and should the incrustation 
happen to crack, and allow the water to reach the red hot metal, so 
violent a disengagement of steam follows, that boilers have been known 
to burst under the sudden pressure. But even though this calamity be 
escaped, the wear and tear of the boiler is very much increased in conse- 
quence of the formation of this deposit, since its hardness often renders 
it necessary to detach it with the hammer, much to the injury of the iron 
boiler-plates, which are also subject to increased oxidation and corrosion, 
in consequence of the high temperature which the incrustation permits 
them to attain by preventing their contact with the water. Many propo- 
sitions have been brought forward for the prevention of these incrusta- 
tions ; some substances have been used of which the action appears to 
be purely mechanical, in preventing the aggregation of the deposited 
particles. Clay, saw-dust, and other matters have been employed with 
this view ; but the action of sal-ammoniac, which has also been found 
efficacious, must be explained upon purely chemical principles. When 
this salt is boiled with carbonate of lime, mutual decomposition ensues, 
resulting in the production of chloride of calcium and carbonate of 
ammonia, of which salts the former is very soluble in water, while the 
latter passes off in vapour with the steam.* 

The deposit formed in boilers fed with sea water consists chiefly of sul- 
phate of lime and hydrate of magnesia, the latter resulting from the 
decomposition of the chloride of magnesium present in sea water. 

The incrustations formed in cisterns and pipes by hard water are also 
produced by the carbonates of lime and magnesia deposited in consequence 
of the escape of the free carbonic acid which held them in solution. Many 
interesting natural phenomena may be explained upon the same principle. 
The so-called petrifying springs, in many cases, owe their remarkable 
properties to the considerable quantity of carbonate of lime dissolved in 
carbonic acid which they contain; when any object, a basket, for ex- 
ample, is repeatedly exposed to the action of these waters, it becomes 
coated with a compact layer of carbonate of lime, and thus appears to 
have suffered conversion into limestone. The celebrated waters of the 
Sprudel at Carlsbad, of San-Filij^po in Tuscany, and of Saint Allyre 
in Auvergne, are the best instances of this kind. 

The stalactites and stalagmites, t which are formed in certain caverns 
or natural grottoes (fig. 45), afford beautiful examples of the gradual 
separation of the carbonate of lime from water charged with carbonic acid. 
Each drop of water, as it trickles through the roof of the cavern, becomes 
surrounded with a shell of carbonate of lime, the length of which is 
prolonged by each drop as it falls, till a stalactite is formed, varying in 

* Solutions of the caustic alkalies, of alkaline carbonates, and arsenites, are also occa- 
sionally employed to prevent the formation of incrustations in boilers, 
t From (TTaXuX,oi, to drop ; o-T«\«y/x«, a drop. 



SOLUTION AND CRYSTALLISATION. 



39 



dium were not destroyed, as would be the case if it had combined with a 
non-metallic substance, Graham was inclined to believe in the metallic 
character of hydrogen, or liydrogenium, as he termed it. But since the 
hydrogen is very easily recovered by moderately heating the palladium, 
and the absorption of large volumes of gases by solid bodies without 
alteration in the properties of the latter, is not at all uncommon, the con- 
clusion is scarcely justified. The hydrogen associated with palladium, 
however, has far more active properties than ordinary hydrogen, for it 
often combines spontaneously with the oxygen of the air, and will unite 
with chlorine and iodine even in the dark. 



38. Chemical Eelations of Water to other Substances. — In its 
chemical relations water presents this very remarkable feature, that, 
although it is an indifferent oxide, its combining tendencies extend over 
a wider range than those of any other compound. Its combinations with 
other substances are generally called hydrates. Water combines with 
two of the elementary substances, viz. , chlorine and bromine, forming an 
exception to the general rule, that combination does not take place between 
elementary and compound bodies. No other element is even dissolved by 
water in any considerable quantity. One part of iodine is dissolved by 
500 parts of cold water, but no chemical combination appears to take 
place. Oxygen, hydrogen, and nitrogen are dissolved by water in very 
small quantity, but become only mechanically diffused through it, and 
do not enter into chemical combination. 

When water acts upon a compound body, it may either effect a simple 
solution, or may enter into chemical combination with it. 

Simple solution appears to be a purely physical phenomenon, not 
accompanied, of necessity, by any chemical action. The dissolved sub- 
stance, in such cases, is otherwise unchanged in properties, and there is 
no manifestation of heat, as in cases of chemical combination. On the 
contrary, there is a reduction of temperature, such as is always noticed in 
the merely physical change from the solid to the liquid form. For 
example, common saltpetre (nitre or nitrate of potash), when shaken with 
water, is rapidly dissolved, the water becoming sensibly colder. If fresh 
portions of saltpetre be added till the water is unable to dissolve any 
more, it will be found that 1000 grs. of water (at 60° F.) have dissolved 
about 300 grs. of saltpetre. Such a solution would be called a cold satu- 
rated solution of saltpetre. If the solution be 
set aside in an open vessel, the water will slowly 
pass off in vapour, and the saltpetre will be 
gradually deposited, its particles arranging them- 
selves in the regular geometrical shape of the 
six- sided prism, which is its common crystalline 
form. The crystals of saltpetre do not contain 
any water ; they are anhydrous. 

If saltpetre be added to boiling water (in a 
porcelain evaporating dish, fig. 43), and stirred 
(with a glass rod) until the water refuses to 
dissolve any more, 1000 grs. of water will be 
found to have dissolved about 2000 grs. ; this 
would be called a hot saturated solution. 

As a genera] rule, solids are dissolved more quickly and in 
quantity by hot water than by cold. 




larger 



40 SUPERSATURATED SOLUTIONS. 

One of the commonest methods of crystallising a solid substance con- 
sists in dissolving it in hot water, and allowing the solution to cool slowly. 
The more slowly it cools, the larger and more symmetrical are the crystals. 
A hot saturated solution is not generally the best for crystallising, because 
it deposits the dissolved body too rapidly. Thus, the hot solution of 
saltpetre prepared as above would solidify to a mass of minute crystals 
on cooling; but if 1000 grs. of saltpetre be dissolved in 4 measured 
ounces of boiling water, it will form crystals of two or three inches long 
when slowly cooled (in a covered vessel). If the solution be stirred 
while cooling, the crystals will be very minute, having the appearance 
of a white powder. 

Some solids, however, refuse to crystallise, even from a hot saturated 
solution, if it be kept absolutely undisturbed. 

Sulphate of soda affords a good example of this. If the crystallised sulphate be 
added to boiling water in a flask, as long as it is dissolved, the water will take into 
solution more than twice its weight of the salt, yielding a solution which boils at 
220° F. If this solution be allowed to cool in the open flask, an abundant crystallisa- 
tion will take place, for cold water will dissolve only about one-third of its weight of 
crystallised sulphate. But if the flask (which should be globular) be tightly corked 
whilst the solution is boiling, it may be kept for several days without crystallising, 
although moved about from one place to another. In this condition the solution is 
said to be super-saturated. On withdrawing the cork, the air entering the partly 
vacuous space above the liquid will be seen to disturb the surface slightly, and from 
that point beautiful prismatic crystals will shoot through the liquid until the whole 
has become a nearly solid mass. A considerable elevation of temperature is observed, 
consequent upon the passage from the liquid to the solid form. If the solution of 
sulphate of soda be somewhat weaker, containing exactly two-thirds of its weight of 
the crystals, it may be cooled without crystallising, even in vessels covered with 
glass plates, but a touch with a glass rod will start the crystallisation immediately.* 

Minute solid particles (nuclei) derived from the air appear to be instrumental in 
causing the crystallisation of super-saturated solutions. If the solution of sulphate 
of soda containing two-thirds of its weight of the crystallised salt be allowed to cool 
in a flask closed by a cork furnished with two tubes closed with plugs of cotton wool, 
it will be found that on withdrawing the plugs and blowing air through one of the 
tubes dipping into the solution, crystallisation does not take place, apparently be- 
cause the air has been deprived of the particles capable of causing it ; for if air be 
blown through the same solution with the bellows, it solidifies almost instantane- 
ously. 

A most beautiful illustration of the power of unfiltered air to start crystallisation 
is afforded by a solution of alum which has been saturated at 194° F., and allowed 
to cool in a flask, the mouth of which is closed by a plug of cotton wool. In this 
state it may be kept for weeks without crystallising, but on withdrawing the plug, 
crystallisation will be seen to commence at a few points on the surface immediately 
under the opening of the neck, and will spread slowly from these, octahedral 
crystals of alum of half an inch or more in diameter being built up in a few seconds, 
the temperature, at the same time, rising very considerably. 
_ In the laboratory, stirring is always resorted to in order to induce crystallisa- 
tion, if it does not take place spontaneously. Thus it is usual to test for potash 
in a solution by adding tartaric acid, which should cause the formation of minute 
crystals of bitartrate of potash (cream of tartar), but the test seldom succeeds unless 
the solutions are briskly stirred together with a glass rod. An amusing illustra- 
tion of this is afforded by pouring a solution of tartaric acid into a solution of 
saltpetre, and allowing the clear mixture to run over a large plate of glass. 
Letters traced on the glass with the finger will now be rendered visible by the 
deposition of the crystals of bitartrate of potash upon the glass. 

39. The crystals of sulphate of soda produced in the above experiments 
contain, in a state of combination with the salt, more than half their 
weight of water. Their composition is — 

* It is very remarkable that, if the glass rod has been recently heated, it will not cause 
the crystallisation even after it has been cool for some time. 



WATER OF CRYSTALLISATION. 41 

Anhydrous sulphate of soda (Na 2 O.S0 3 ) 142 parts, or one molecule, 
Water ...... 180 ,, or ten molecules, 

as expressed by the formula jSTa 2 O.SO 3 .10H 2 O. If some of the crystals 
be pressed between blotting paper to remove adhering water, and left 
exposed to the air, they will gradually effloresce, or become covered with a 
white opaque powder. This powder is the anhydrous sulphate of soda into 
which the entire crystals would ultimately become converted by exposure 
to air. Since most crystals containing water have their crystalline form 
destroyed or modified by the loss of the water, it is commonly spoken of 
as icater of crystallisation. 

Coloured salts, containing water of crystallisation, generally change 
colour when the water is removed. The sulphate of copper (blue stone) 
affords an excellent example of this. The beautiful blue prismatic crystals 
of this salt contain 

Anhydrous sulphate of copper (CuO.S0 3 ) 159*5 parts, or one molecule, 
Water ...... 90*0 ,, or five molecules. 

as expressed by the formula CuO.S0 3 .5H.,0. 

When these are exposed to the air at the ordinary temperature they 
remain unchanged ; but if heated to the boiling-point of water, the} 7 " 
become opaque, and may be easily crumbled down to a white powder. 
This powder contains 

Anhydrous sulphate of copper (CuO.S0 3 ) 159 "5 parts, or one molecule, 
Water . . . . . . 18 ,, or one molecule, 

and would therefore be represented by CuQ.SOj..H 2 0. The four 
molecules of water, which have been expelled, constituted the water of 
crystallisation, upon which the form and colour of the sulphate of 
copper depend. If the Tvhite powder be moistened with water, com- 
bination takes place, with great evolution of heat, and the blue colour is 
reproduced. The one molecule of water which still remains, is not 
expelled until the salt is heated to 390° F. (199° C), proving that it 
is held to the sulphate of copper by a more powerful chemical attraction. 
On this account it is spoken of as icater of constitution, and in order that 
the formula of the salt may exhibit the difference between the water of 
constitution and of crystallisation, it is usually written 
CuO . S0 3 . H 2 . 4Aq.* 

(Definition. — Water of crystallisation of salts is that which is generally 
expelled at 212° F. (100° C), and is connected with the form and colour 
of the crystals. Water of constitution is not generally expelled at 212° 
F., and is in more intimate connection with the chemical properties of 
the salt.) 

Several of the so-called sympathetic inks employed for writings which 
are invisible until heated, depend upon the change of colour which results 
from the loss of water of crystallisation. Characters written with a weak 
solution of chloride of cobalt and allowed to dry, are very nearly in- 
visible, since the pink colour of so small a quantity of the salt is scarcely 
noticed ; but on warming the paper, the pink hydrated chloride of cobalt 
(CoCl 2 .2Aq.) loses its water of crystallisation, and the blue anhydrous 
chloride of cobalt is produced. On exposure to air this again absorbs 
water, and the writing fades away. 

Some salts have so great a tendency to combine with water, that they 

* A qua, water. 



42 HYDRATES — NATURAL WATERS. 

become moist or deliquesce when exposed to air. This deliquescence is 
exhibited in a marked degree by chloride of calcium, and its great attrac- 
tion for water is turned to advantage in drying air and other gases by 
passing them through tubes filled with the salt. 

40. Most bases are capable of combining with water to form hydrates, 
as exemplified in the slaking of lime. Anhydrous lime or quick-lime 
(CaO), when wetted with water, combines with it, evolving much heat, 
and crumbling to a loose bulky powder, which is hydrate of lime or slaked 
lime (CaO.H 2 0). At a red heat the water is expelled, and anhydrous 
lime remains. 

The hydrates of potash, soda, and baryta, however, do not lose their 
water when heated, which has led some chemists to entertain the belief 
that they do not really contain water as such, but that they have been 
formed from water by the substitution of a metal for a portion of its 
hydrogen. Upon this view, the hydrate of potash, instead of being re- 
presented by the formula K 2 O.H 2 0, would be KHO, or water (H 2 0), 
in which potassium has been substituted for half the hydrogen. 

41. Nearly all the acids are capable of forming hydrates. Indeed, as 
a general rule, the hydrated form of an acid is that in which it is com- 
monly obtained and used, the anhydrous acid being usually of very 
secondary importance. Thus, the liquid used under the name of concen- 
trated sulphuric acid is the hydrate of that acid (H 2 O.S0 3 ), the anhydrous 
sulphuric acid (S0 3 ) being a crystalline solid of no use except to the 
chemist, and not manifesting any acid properties until brought into contact 
with water, with which it combines with evolution of much heat. The 
hydrated sulphuric acid (H 2 O.SOJ does not lose its water when heated, 
but distils unchanged, and some chemists are of opinion that the hydrogen 
is not contained in it in the form of water, but that the so-called hydrated 
sulphuric acid should be represented as H 2 S0 4 , so as not to indicate that 
it contains water. The acid is thus represented as a unitary compound 
(formed of one group), instead of a binary compound of the groups H 2 
and S0 3 . Convenient as this view is sometimes found in notation and in 
theoretical speculations, the circumstance that S0 3 is known in the separate 
state, and yields the hydrated sulphuric acid when brought in contact 
with water, causes the latter view still to find favour among many 
practical chemists. 

The hydrated sulphuric acid (H 2 O.S0 3 ) has a very powerful attraction 
for more water, which leads to its employment in the laboratory for 
drying air and gases, as well as for producing many chemical changes 
which depend upon the abstraction of water or its elements {dehydration). 
If concentrated sulphuric acid (oil of vitriol) be poured into water, the 
mixture will become very hot, in consequence of the combination between 
the two liquids. The water should be stirred whilst the acid is being 
poured in, as the sudden mixture of considerable quantities might cause 
danger from the projection of the liquid. 

42. Water from Natural Sources. — Pure water is not found in 
nature. Rain is the purest form of natural water, but contains certain 
gases which it collects from the atmosphere during its fall. As soon as 
it reaches the earth, it begins to dissolve small portions of the various 
solid materials with which it comes in contact, and thus becomes charged 
with salts and other substances to an extent varying, of course, with the 



SYNTHESIS OF WATER. 



35 



of hydrogen combine with one volume of oxygen to form two volumes of 
aqueous vapour, at the same temperature and pressure. 

The combination of hydrogen and oxygen in a vessel heated above 
the boiling-point of water is effected in the apparatus contrived by Dr 
Hofmann, and represented in fig. 38, where the closed limb of the eudio- 
meter is surrounded by a tube through which the vapour of boiling 
fousel oil, having a temperature of 270° F., is passed from a flask con- 
nected with the wide tube by a cork and a short wide piece of bent glass 
tubing, jacketed with caoutchouc 
to prevent loss of heat. The 
vapour of fousel oil passes out 
of the wide tube through the 
tube t which enters the cork at 
the bottom, and conducts the 
vapour into a glass worm (w) im- 
mersed in a jar through which 
cold water is allowed to flow, as 
shown by the arrows. The closed 
limb of the eudiometer having 
been filled with mercury, a small 
quantity of the mixture of hydro- 
gen and oxygen obtained from the 
voltameter (fig. 36) is introduced 
into it through a tube passed 
down the open limb, the dis- 
placed mercury being run out 
through the tube c, which is 
closed by a nipper-tap. The 
closed limb is then heated oy the 
vapour, and the mercury in the 
two limbs levelled from time to 
time by running a little out 




Synthesis of water above 212° 



through c, until the gas in the closed limb no longer expands. Its volume 
is then observed, an inch more mercury poured into the open limb, which 
is then tightly closed by a cork, and the spark from the induction-coil is 
passed by the wires — and + . After the explosion the cork is removed, 
and the mercury levelled in the two limbs, when the volume of the steam 
will be found to be just two-thirds of the volume of the gas before explo- 
sion. On cooling down, the steam condenses, and the mercury entirely fills 
the closed limb of the eudiometer. 

That 2 volumes of steam should contain 2 volumes of hydrogen and 1 
volume of oxygen would appear, on physical grounds, impossible, since 
two bodies cannot occupy the same space at the same time ; but it must 
be remembered that the two bodies in question have lost their indi- 
viduality in consequence of their chemical combination, by which they 
have become one body — water. 

A distinction must be carefully drawn between the ultimate physical 
particles (molecules) and the ultimate chemical particles (atoms) of any 
form of matter. The smallest conceivable particle of steam, incapable 
of further mechanical subdivision, would yet be capable of being divided 
by chemical means into 2 atoms of hydrogen and 1 atom of oxygen. 

On comparing steam with hydrogen, it is found that they are expanded 
in the same degree by heat, and contracted in the same degree by cold 



36 ATOMS AND MOLECULES. 

or pressure, provided that the steam is always at a temperature remote 
from its condensing point. Hence it appears that equal volumes of steam 
and hydrogen contain the same number of molecides or ultimate physical 
atoms. 

(1.) Suppose Y volumes of steam to contain M molecules, 

(2.) Then V volumes of hydrogen contain M molecules ; 

(3.) But M molecules of steam contain 2 M atoms of hydrogen ; 

(4.) Therefore (by 1), V volumes of steam contain 2 M atoms of 

hydrogen. 
(5.) But V volumes of steam contain V volumes of hydrogen ; 
(6.) Therefore, V volumes of hydrogen contain 2 M atoms of hydrogen, 
(7.) And (by 2) Y volumes of hydrogen contain M molecules; 
(8.) Therefore, 2 M atoms of hydrogen = M molecules, 
or 2 atoms of hydrogen = 1 molecule. 

By precisely similar reasoning it may be shown that the molecule, or 
smallest conceivable physical particle of oxygen, must be composed of 2 
atoms of oxygen. Hence, the important conclusion is arrived at that the 
molecule or ultimate physical particle of matter, whether elementary or 
compound, occupies, in the state of gas or vapour, twice the volume occupied 
by an atom of hydrogen. Thus, 







Volume. 


Weight 


Atom of hydrogen 


= H 


= 1 


1 


Atom of oxygen 


= 


= 1 


= 16 


Molecule of hydrogen = 


= H 2 


= 2 


2 


Molecule of oxygen 


- o, 


= 2 


- 32 


Molecule of steam 


= H 2 


= 2 


= 18 



Since the molecule of a compound body in the state of gas or vapour 
occupies 2 volumes, and the specific gravity is the weight of 1 volume, 
half the molecular weight of a compound gas or vapour will give its specific 
gravity referred to hydrogen as the standard. 

Thus, the molecular weight of steam being 18, its specific gravity 
(H = 1) would be 9. 

If the specific gravity in relation to air be required, it may be obtained 
by multiplyiug the specific gravity referred to hydrogen by , 0692, which 
represents the specific gravity of hydrogen referred to air as the unit. 

The above considerations help to explain the indisposition of hydrogen 
and oxygen to combine at the ordinary temperature, for the molecule 
of hydrogen (H 2 ) combines with the atom of oxygen, so that the two 
atoms of this element which are contained in the molecules must be 
separated in order to combine with the hydrogen. 

34. The synthesis of water by weight cannot be effected with accuracy 
by weighing the gases themselves, on account of their large volume. It 
is, therefore, accomplished by passing an indefinite quantity of hydrogen 
over a known weight of pure hot oxide of copper, when the hydrogen 
combines with the oxygen of the oxide to form water. The loss of weight 
suffered by the oxide of copper gives the amount of oxygen ; and if this 
be deducted from the weight of the water, that of the hydrogen will be 
ascertained. 

The apparatus employed for this purpose is represented in fig. 39. h is the bottle 



RECIPROCAL COMBUSTION 



37 



in which hydrogen is generated from diluted sulphuric acid and zinc ; the gas passes 
in p through solution of potash, which absorbs any sulphuretted hydrogen ; then 
through s, containing pumice stone (used on account of its porous character), saturated 
with a strong solution of nitrate of silver, which removes arsenic and antimony from 
the hydrogen ; the gas then passes through vv, containing pumice saturated with oil 




Fig. 



-Synthesis of water by weight. 



of vitriol to absorb moisture . The bulb c, with the oxide of copper, is weighed before 
and after the experiment, as are the globe g, for condensing the water, and the tube 
t, containing pumice and oil of vitriol, to absorb the aqueous vapour. Of course, the 
bulb c must not be heated until the hydrogen has displaced all the air from the 
apparatus. 

35. It is evident that, although hydrogen is generally designated the 
combustible gas, and oxygen the supporter of combustion, the application 
of these terms depends entirely upon circumstances, since the phenomenon 
of combustion is a reciprocal operation in which both, elements have an 
equal share. 

This may be illustrated by a simple experiment. The hydrogen and oxygen reser- 
voirs,* H and O, fig. 40, are connected with two bent glass tubes passing through a 
cork into an ordinary lamp glass c, upon 
the upper opening of which a pi?ce of tin- 
plate is laid. In order to prevent the 
ends of the glass tubes from being fused 
by the burning gases, little platinum 
tubes, made by rolling up pieces of 
platinum foil, are placed in the orifices, 
and the glass is melted round them by 
the blowpipe flame. The hydrogen being 
lighted, and the oxygen turned on to 
about the same extent, the lamp-glass is 
placed over the cork, when the hydrogen 
burns steadily. If the oxygen be slowly 
turned off, the flame will gradually leave 
the hydrogen tube and come over to the 
oxygen, which will continue burning in 
the atmosphere of hydrogen. By again 
turning on the oxygen, the flame may be 
sent over to the hydrogen tube. With 
a little care the flame may be made to 
occupy an intermediate position between 
the two burners, and to leap from one to the other at pleasure. 

36. The great energy with which hydrogen combines with oxygen is 
turned to account for the purpose of producing the highest temperature 
which can be obtained by any chemical process. 

The oxyhydrogen blowpipe (fig. 41) is an apparatus for burning a jet of hydrogen 
mixed with half its volume of oxygen. The gases are supplied from separate gas- 

* These are the wrought iron vessels in which hydrogen and oxygen are condensed under 
the pressure of a few atmospheres by Mr Orchard of Kensington. They are far more con- 
venient than gas-bags or gas-holders. 




Reciprocal combustion. 



38 



OXYHYDKOGEN BLOWPIPE. 




Pig. 41. — Oxyhydrogen blowpipe. 



holders (or bags with pressure -boards and weights) through the tubes H and 0, which 

conduct them into the brass sphere B. Each of these 
■L . tubes is provided with a valve of oiled silk opening 

outwards, so as to prevent the passage of either gas 
into the receptacle containiug the other. The tube 
A is stuffed with thin copper wires, which would 
rapidly conduct away the heat and extinguish the 
flame of the mixed gases burning at the jet, 
should it tend to pass back and ignite the mixture 
in B. The stop-cocks D and E allow the flow of 
the gases to be regulated so that they may mix in 
the right proportions. If the hydrogen be kindled 
first, it will be found that, as soon as the oxygen 
is turned on, the flame is reduced to a very much 
smaller volume, because the undiluted oxygen 
required to maintain it occupies only one-fifth 
of the volume of the atmospheric air from which 
the hydrogen was at first supplied with oxygen. The heat developed by the com- 
bustion being therefore distributed over a much smaller area, the temperature at 
any given point of the flame must be much higher, and very few substances are 
capable of enduring it without fusion.* Lime is one of these ; and if a cylinder of 
lime be supported, as at L, fig. 41, in the focus of the flame, its particles become 
heated to incandescence, and a light is obtained which is visible at night from very 
great distances, so as to be well adapted for signalling and lighthouses. For such 
purposes coal-gas is often used instead of hydrogen {oxycalciam light). 

If a shallow cavity be scooped in a lump of quicklime, a few scraps of platinum placed 
in it, and exposed to the oxyhydrogen flame (fig. 42), a fused globule of platinum of very 

considerable size may be obtained in a few seconds. 
By employing alittlefurnacemadeof lime, Devillehas 
succeeded in fusing platinum in quantities sufficient 
to cast large ingots, a result unattainable by any 
other furnace. Pipeclay, which resists the action of 
all ordinary furnace-heats, may be fused into a glass 
in this flame, whilst gold and silver are instan- 
■p-^ In taneously melted, and vaporised into a dense smoke. 

37. In its chemical relations to other elements, hydrogen is diametri- 
cally opposed to oxygen. Whereas the latter combines directly with the 
greater number of the elements, hydrogen will enter into direct combina- 
tion with very few ; oxygen, chlorine, bromine, iodine, carbon, and sulphur 
(the three last with difficulty), are the only elements which unite in a 
direct manner with hydrogen, and of these only chlorine and bromine 
combine with hydrogen at the ordinary temperature, though not without 
exposure to light. Again, whilst fluorine is not known to form any com- 
pound with oxygen, its combination with hydrogen (hydrofluoric acid) is 
one of the most stable compounds known, and it may be safely asserted 
that fluorine in the free state would combine with hydrogen even more 
readily than chlorine does. All the metals form compounds with oxygen, 
but very few combinations of metals with hydrogen have been obtained. 
Indeed, in its relations to other elements, hydrogen closely resembles the 
metals, though it does not fall within the definition of a metal given 
above, since it does not form a base with oxygen, and its combinations 
with the salt-radicals (chlorine, &c.) are acids, and not salts. 

In the course of some experiments upon the power possessed by metals 
of absorbing (or occluding) gases at high temperatures and retaining them 
after cooling, Graham found that the metal palladium could be made to 
absorb nearly one thousand times its volume of hydrogen at the tempera- 
ture of boiling water. Finding that the metallic characters of the palla- 




* The temperature of this flame has been estimated at about 14,000° F. 



SOFTENING OF WATERS. 



47 



colour according to the nature of the substances which are separated 
from the water together with the carbonate of lime (such as the oxides 
of iron and vegetable 



%># 




sSfi^H ^R&igP? 



Fig. 45.— Stalactite cavern. 



iron 
matter) ; and as each drop 
falls from the point of the 
stalactite upon the floor of 
the cavern, it deposits 
there another shell of car- 
bonate of lime, which 
grows, like the upper one, 
but in the opposite direc- 
tion, and forms a stalag- 
mite, thus adorning the 
grotto with conical pillars 
of carbonate of lime, some- 
times, as in the case of the 
oriental alabaster, varie- 
gated with red and yellow, 
and applicable to orna- 
mental purposes. 

When water which has 
been boiled for some time is 

compared with unboiled water from the same source, it will be found to have 
become much softer, and this can now be easily explained, for, a consider- 
able proportion of the salts of lime and magnesia having separated from the 
water, the latter is not capable of decomposing so. large a quantity of soap. 
The amount of hardness which is thus destroyed by boiling is generally 
spoken of as temporary hardness, to distinguish it from the permanent 
hardness due to the soluble salts of lime and magnesia which still remain 
in the boiled water. It is customary with analytical chemists, in report- 
ing upon the quality of natural waters, to express the hardness by a cer- 
tain number of degrees which indicate the number of grains of chalk or 
carbonate of lime which would be dissolved in a gallon of water contain- 
ing carbonic acid, in order to render its hardness equal to that of the 
water examined, that is, to render it capable of decomposing an equal 
quantity of soap. Thus, when a water is spoken of as having 16 degrees 
hardness, it is implied that 1 6 grs. of carbonate of lime dissolved in a 
gallon of water, containing carbonic acid, would render that gallon of 
water capable of decomposing as much soap as a gallon of the water under 
consideration. 

The utility of a water for household purposes must be estimated, there- 
fore, not merely according to the total number of degrees of hardness 
which it exhibits, but also by the proportion of that hardness which may 
be regarded as temporary, that is, which disappears when the water is 
boiled. Thus the total hardness of the ISTew Eiver water amounts to 
nearly 15 degrees, that of the Grand Junction Company to 14 degrees, and 
yet these waters are quite applicable to household uses, since their hard- 
ness is reduced by boiling to about 5 degrees. It has been ascertained 
that every degree of hardness in water gives rise to a waste of about 10 
grs. of soap for every gallon of water employed, and hence the use of 100 
gallons of Thames or !New Eiver water in washing will be attended with 
the loss of about 2 lbs. of soap ; this loss is reduced, however, to about 
one-third when the temporary hardness has been destroyed by boiling. 



48 ACTION OF WATER ON LEADEN CISTERNS. 

The addition of washing soda (carbonate of soda) removes not only the 
temporary, but also the permanent hardness due to the presence of the 
sulphates of lime and magnesia in the water, for both these salts are de- 
composed by the carbonate of soda, which separates the lime and mag- 
nesia as insoluble carbonates, while sulphate of soda remains dissolved in 
the water.* The household practice of boiling the water, and adding a 
little washing soda, is therefore very efficacious in removing the hard- 
ness. Clark's process for softening waters depends upon the neutralisa- 
tion of the free carbonic acid contained in the water by the addition of a 
certain quantity of lime ; the lime thus added combines with the free 
carbonic acid, and the carbonate of lime so produced separates together 
with the carbonates of lime and magnesia, which were previously retained 
in solution by the free carbonic acid ; this process, therefore, affects chiefly 
the temporary hardness ; moreover, the earthy carbonates which are sepa- 
rated appear to remove from the water a portion of the organic matter 
which it contains, and thus effect a very important purification. The 
water under treatment is mixed, in large tanks, with a due proportion of 
lime previously diffused through water (the quantity necessary having 
been determined by preliminary experiment), and the mixture allowed to 
settle until perfectly clear, when it is drawn off into reservoirs. f 

Waters which are turbid from the presence of clay in a state of sus- 
pension, are sometimes purified by the addition of a small quantity of 
alum or sulphate of alumina, when the alumina is precipitated by the car- 
bonate of lime, and carries down with it mechanically the suspended clay, 
leaving the water clear. 

The organic matter contained in waters may be vegetable matter dis- 
solved from the earth, with which it has come in contact, or resulting 
from the decomposition of plants, or it may be animal matter derived 
either from the animalcules and fish naturally existing in it, or from the 
sewage of towns,. and, in the case of well waters, from surface drainage. 
It is a pretty generally received opinion that such of these organic matters 
as are very susceptible of chemical change have an injurious effect upon 
the system of persons drinking the water, and it is now usual, in ex- 
amining water as to its fitness for consumption, to ascertain how much of 
the organic matter is in a changeable condition, by determining with the 
aid of a solution of permanganate of potash the amount of oxygen neces- 
sary to effect its conversion into more stable forms. 

It is believed, upon good medical authority, that cholera and diarrhoea 
are propagated by certain spores or germs, which are present in the eva- 
cuations of persons suffering from those maladies, and are conveyed into 
water which is allowed to become contaminated by sewage. 

44. One of the most important points to be taken into account in 
estimating the qualities of a water is its action upon lead, since this metal 
is unfortunately so generally employed for the storage and transmission of 
water, and cases frequently occur in which the health has been seriously 
injured by repeated small doses of compounds of lead taken in water, 
which has been kept in a leaden cistern. If a piece of bright, freshly 
scraped lead be exposed to the air, it speedily becomes tarnished from the 
formation of a thin film of the oxide of lead, produced by the action of 

* CaO . S0 3 + Na 2 . C0 2 = Na 2 . S0 3 + CaO . C0 2 . 

Sulphate of lime. Carbonate of soda. Sulphate of soda. Carbonate of lime. 

t Thames and New River water are softened, in this way, to 3°\ r >, or to a lower point 
than by an hour's boiling. 



MINERAL WATEKS — SEA WATER. 49 

the atmospheric oxygen ; this oxide of lead is soluble in water to some 
extent, and hence, when lead is kept in contact with water, the oxygen 
which is dissolved in it acts upon the metal, and the oxide so produced 
is dissolved by the water ; but, fortunately, different waters act with very 
different degrees of rapidity upon the metal, according to the nature of 
the substances which they contain. 

The film of oxide which forms upon the surface of the lead is in- 
soluble, or nearly so, in water containing much sulphate or carbonate of 
lime, so that hard waters may generally be kept without danger in leaden 
cisterns ; but soft waters, and those which contain nitrites or nitrates, 
should not be drunk after contact with lead. Nearly all waters which 
have been stored in leaden cisterns contain a trace of the metal, and since 
the action of this poison, in minute doses, upon the system is so gradual 
that the mischief is often referred to other caus.es, it is much to be desired 
that lead should be discarded altogether for the construction of cisterns. 

Mineral waters, as they are popularly called, are simply spring waters 
containing so large a quantity of some ingredient as to have a decided 
medicinal action. They are differently named according to the nature of 
their predominating constituent. Thus, a chalybeate water contains a con- 
siderable quantity of a salt of the oxide of iron (usually the carbonate dis- 
solved by free carbonic acid) ; an acidulous water is distinguished by a 
large proportion of carbonic acid, and is well exemplified in the celebrated 
Seltzer water ; a sulphureous or hepatic water has the nauseous odour due 
to the presence of sulphuretted hydrogen. The Harrogate water is emi- 
nently sulphureous. Saline waters are such as contain a large quantity 
of some salt ; thus the saline springs of Cheltenham are rich in common 
salt and sulphate of soda. 

The chalybeate waters, which are by no means uncommon, become 
brown when exposed to the air, and deposit a rusty sediment which con- 
sists of the sesquioxide of iron, formed by the union of the oxygen of the 
air with the oxide of iron existing in the carbonate.* 

45. Sea water contains the same salts as are found in waters from other 
natural sources, but is distinguished by the very large proportion of chlo- 
ride of sodium (common salt). A gallon of sea water contains usually 
about 2500 grains of saline matter, of which 1890 grains consist of common 
salt. The circumstance that clothes wetted with sea water never become 
perfectly dry is to be ascribed chiefly to the chloride of magnesium present 
in the water, which is distinguished by its tendency to deliquesce or become 
damp in moist air. There are two elements, bromine and iodine, which 
are found combined with metals in appreciable quantity in sea water, 
though they are of somewhat rare occurrence in other waters derived from 
natural sources. 

46. By distillation, pure water may be obtained from most spring and 
river waters. 

(Definition. — Distillation is the conversion of a liquid into a vapour, 
and its recondensation into the liquid form in another vessel.) 

Fig. 46 represents the ordinary form of still in common use, in which A is a copper 
boiler containing the water to be distilled ; B the head of the still, which lifts out at 
b, and is connected by the neck C with the worm D, a tin pipe coiled round in the 
tub E, and issuing at F. The steam from the boiler, passing into the worm, is con- 



2(FeO.C0 2 ) + + H 2 0- .= __Fe a O,.H s O_ + 2C0 2 

c a 
D 



Carbonate of iron. Water. ^^tf toS?" Carbonic acict. 



50 



DISTILLATION, 



=^J? 



densed to the liquid state, being cooled by the water in contact with the worm ; this 
water, becoming heated, passes off through the pipe G, being replaced by cold water, 
which is allowed to enter through H.* . 

Another form of apparatus for distillation of water and other liquids is shown m 

fiff 47 A is a stoppered retort, the neck of which fits into the tube of a Liebig s con- 

8 * ' rr denser (B), which 

consists of a glass 
tube (C) fitted < by 
means of corks into 
a glass, copper, or 
tinned iron tube 
(D), into which a 
stream of cold water 
is passed by the 
funnel E, the heated 
water running out 
through the upper 
tubeF. The water 
furnished by the 
condensation of 
the steam passes 
through the quilled 
receiver G, into the 
flask H. Heat is 
gradually applied 
to the retort by a 
ring gas-burner. 

Many special precautions are requisite in order to obtain absolutely pure 
distilled water for refined experiments, but for ordinary purposes the com- 
mon methods of distillation yield it in a sufficiently pure condition 

The saline matters present in the water are of course left behind in the 
still or retort. Sea water is now frequently distilled on board-ship when 





Fig. 47.— Distillation— Liebig's condenser. 

fresh water is scarce. The vapid and disagreeable taste of distilled water, 
which is due to its having been deprived of the dissolved air during the 
distillation, is remedied by the use of Normandy's apparatus, which pro- 
vides for the restoration of the expelled air. 

* A rosette gas-burner (K) on Bunsen's principle is very convenient for a small still of 
this description. 



PEROXIDE OF HYDROGEN. 51 

47. The physical properties of water are too well known to require any- 
detailed description. Its specific gravity in the liquid state is = 1, being 
taken as the standard to which the specific gravities of liquid and solid 
bodies are referred. 

(Definition. — The specific gravity of a liquid or solid body is its weight 
as compared with that of an- equal volume of pure water at 60° F., 
15°-5 C.) 

Water assumes the solid form, under ordinary circumstances, at 32° F. 
(0° C), and may be obtained in six-sided prismatic crystals. Snow con- 
sists of beautiful stellate groupings of these crystals. Ice has the specific 
gravity 0*9184. In the act of freezing, water expands very considerably, 
so that 174 volumes of water at 60° F. become 184 volumes of ice. The 
breakage of vessels, splitting of rocks, &c, by the congelation of water, 
are due to this expansion. Water passes off- in vapour at all tempera- 
tures, the amount of vapour evolved in a given time of course increasing 
with the temperature. The boiling point of water is 212° F. (100° C.) 

(Definition. — The boiling point of a liquid is the constant tempera- 
ture indicated by a thermometer, immersed in the boiling liquid in the 
presence of a coil of platinum wire, to facilitate disengagement of vapour, 
and at a pressure of 30 in. (762 mm.) Bar.) 

At and above 212° F. at the ordinary atmospheric pressure (30 in. Bar.), 
water is an invisible vapour of specific gravity 0-622 (air — 1). One cubic 
inch of water at 60° F. becomes 1696 cubic inches of vapour at 212° F. 

48. Binoxide or peroxide of hydrogen or oxygenated water, H 2 2 . This compound 
is not met with in nature, nor lias it any important useful application in the arts. 
It has recently, however, acquired some importance as- a medicinal agent, and it 
possesses very great interest for the student of chemical philosophy, because it helps 
to throw some light upon the atomic constitution of the elements. 

To prepare the peroxide of hydrogen, some baryta (BaO) is heated in a current of 
oxygen, when it becomes converted into the peroxide of barium (Ba0 2 ). If this be 
powdered, suspended in water, and acted upon by a stream of carbonic acid gas, the 
water becomes charged with the peroxide of hydrogen ; Ba0 2 + H 2 + C0 2 = 
BaO . C0 2 + H 2 2 . The carbonate of baryta is allowed to subside, and the clear 
solution of peroxide of hydrogen poured off. 

If a little powdered binoxide of manganese be thrown into the solution, brisk 
effervescence will ensue from the escape of oxygen, which may be recognised by the 
usual test with a partly extinguished match. The binoxide of manganese does not 
appear to be decomposed in this experiment, the whole of the oxygen being derived 
from the peroxide of hydrogen dissolved in the water, which is immediately decom- 
posed, by contact with the binoxide of manganese, into water and free oxygen. If a 
solution of permanganate of potash be poured into a cylinder partly filled with the 
liquid, it will cause a rapid evolution of oxygen, derived not only from the peroxide 
of hydrogen, but from the permanganic acid, the red colour of which disappears, 
because it becomes reduced to a lower oxide of manganese. 

The usual method of preparing peroxide of hydrogen in a pure state, consists in 
decomposing the peroxide of barium with diluted hydrochloric acid, under certain 
precautions to avoid the decomposition of the very unstable peroxide of hydrogen. 
Its formation is represented by the equation Ba0 2 + 2HC1 = H 2 2 + BaCl 2 . The 
chloride of barium is removed from the solution by the cautious addition of sulphate 
of silver, which precipitates the barium as sulphate of baryta, and the silver as 
chloride of silver, thus, BaCl 2 + Ag 2 O.S0 3 = 2AgCl + BaO.SO a . The precipitates 
are allowed to subside, and the clear liquid evaporated in the exhausted receiver of 
the air-pump over a dish of oil of vitriol to absorb the water, which evaporates much 
more rapidly than the peroxide. The pure peroxide of hydrogen is a syrupy liquid 
of sp. gr. 1*453, with a, very slight chlorous odour. Its most remarkable feature is 
the facility with which it is decomposed into water and oxygen.* Even at 70° F, 

* The presence of a little free acid renders it rather more stable, whilst free alkali has 
the opposite effect. A. solution of peroxide of hydrogen, containing a little hydrochloric 
acid, is now sold for medicinal and photographic uses. 



52 OZONE.. 

it begins to evolve bubbles of oxygen, so that it can scarcely be prepared in hot 
weather. At 212° it decomposes with violence. The mere contact with certain 
metals, such as gold, platinum, and silver, which have no direct attraction for oxy- 
gen, will cause the decomposition of the peroxide of hydrogen, without any chemical 
alteration of the metal itself.* It was noticed above that the binoxide of manganese 
decomposes it without undergoing any apparent change. The most surprising 
effect is that which takes place with oxide of silver. If a drop of peroxide of hydro- 
gen be allowed to fall upon oxide of silver, which is a brown powder, decomposition 
takes place with explosive violence and great evolution of heat, the oxide of silver 
losing its oxygen, and becoming grey metallic silver. The oxides of gold and 
platinum are acted upon in a similar manner. 

These very extraordinary changes, which were formerly described as catalytic 
actions, are now generally accounted for by the hypothesis that the oxygen in the 
oxide of silver, &c. , exists in a condition different from that of the second atom of 
oxygen in the peroxide of hydrogen, and that these two conditions of oxygen 
have a chemical attraction for each other, similar to that which exists between 
different elements. If the oxygen in the oxide of silver be represented as electro- 
negative oxygen (see 5), as its relation to the metal would lead us to expect, and 
the second atom of oxygen in the peroxide of hydrogen be represented as electro- 
positive oxygen, the mutual decomposition of the two compounds might be repre- 
sented by the equation, 

Ag 2 + H 2 00 = Ag 2 + H 2 + 0. 
+ - + 

This would support the conclusion arrived at by the train of reasoning 
at page 36, that the molecule or ultimate particle of free oxygen is really 
composed of two atoms. 

49. Ozone. — This is the name given to a modified form of oxygen, of the true 
nature of which there is still some doubt, as it has never been obtained unmixed with 
ordinary oxygen, but it appears to be formed by the union of three atoms of oxygen 
(occupying three volumes), to produce a molecule of ozone (occupying two volumes). 
Just as peroxide of hydrogen (H 2 2 ), maybe regarded as formed by the combination of 
a molecule of water (H 2 0) with an atom of oxygen, so ozone may be viewed as a 
combination of a molecule of oxygen (0 2 ) with an atom of oxygen. It would then be 
half as heavy again as ordinary oxygen, and experiment has shown that its rate of 
diffusion is in accordance with this view. 

It derives its name from its peculiar odour (oZ,uv, to smell). Oxygen appears to be 
capable of assuming this ozonised condition under various circumstances, the principal 
of which are, the passage of silent electric discharges, t and the contact with sub- 
stances (such as phosphorus) undergoing slow oxidation in the presence of water. 
A minute proportion of the oxygen obtained in the decomposition of water by 
the galvanic current also exists in the ozonised condition, as may be perceived by its 
odour. 

The use of Siemens' induction tube (fig. 48) affords the readiest method of demon- 
strating the characteristic properties of ozone. This apparatus consists of a tube (A) 

coated internally with tin- 
foil (or silvered on the in- 
side), and surrounded with 
another tube (B), which is 
coated with tin-foil on the 
outside. When the inner 
and outer coatings are 
placed in connexion with 
the wires of an induction 
coil by means of the screws 
(CD), and a stream of air 
or oxygen is passed through 
(E) between the two tubes, 
Fig. 48.— Tube for ozonising air by induction. a strong odour is perceived 

at the orifice (F). 
One of the best chemical tests for ozone is a damp mixture of starch with iodide 

* Such inexplicable changes as this are sometimes included under the general denomina 
tion of catalysis, or decomposition by contact. 

t It is the odour of ozone which is perceived in working an ordinary electrical machine. 




PROPERTIES OF OZONE. 53 

of potassium. 100 grains of starch are well mixed in a mortar with a measured 
ounce of cold water, and the mixture is slowly poured into five ounces of boiling 
water in a porcelain dish, with occasional stirring. The thin starch-paste thus 
obtained is allowed to cool, and a few drops of solution of pure iodide of potassium 
are added, the mixture being well stirred with a glass rod. If this mixture be 
brushed over strips of white cartridge paper, these will remain unchanged in 
ordinary air ; but when they are exposed to ozonised air (such as that which has 
passed through the induction tube), they will immediately assume a blue colour. 
The ozonised oxygen being more active, or endowed with more powerful chemical 
attractions than ordinary oxygen, abstracts the potassium from the iodide of 
potassium (KI), and sets free the iodine, which has the specific property of impart- 
ing a blue colour to starch. The intensity of the blue tint is proportionate to the 
quantity of iodine liberated, and therefore to that of the ozonised oxygen pre- 
sent, and hence, by reference to a standard scale of colours previously agreed upon, 
the ozone may be expressed in degrees. The result, however, is affected by so many 
trifling circumstances, that it is doubtful whether such determinations of the quantity 
of ozone are to be considered trustworthy. If the ozonised air issuing from F be 
passed into a solution of indigo (sulphindigotic acid largely diluted) the blue colour 
will soon disappear, since the ozone oxidises the indigo, and gives rise to products 
which, in a diluted state, are nearly colourless. Ordinary oxygen is incapable of 
bleaching indigo in this manner. If the ozone is passed through a tube of vul- 
canised caoutchouc, this will soon be perforated by the corrosive effect of the ozone, 
whilst ordinary oxygen would be without effect upon it. 

If the ozone from F be made to pass slowly through a glass tube heated in the 
centre by a spirit-lamp, it will be found to lose its power of affecting the iodised 
starch-paper, the ozone having been reconverted into ordinary oxygen under the 
influence of heat. A temperature of 300° F. is sufficient to effect this change. It 
has been observed that a given volume of oxygen diminishes when a portion of it is 
converted into ozone by the silent electric discharge, and that it regains its original 
volume when the ozone is reconverted by heat, proving that the ozonised form of 
oxygen is denser, or occupies less space than the ordinary form. 

When a measured volume of pure oxygen was ozonised by the silent electric dis- 
charge until its volume had decreased by one-twelfth, and the ozone thus formed was 
absorbed by turpentine, it was found that two volumes of ozone had been pro- 
duced from three volumes of oxygen. 

On shaking the ozonised oxygen with mercury, the latter became partly converted 
into oxide, and the ozone disappeared, but there was no alteration in the volume of 
the oxygen, for (2 vols, ozone) 2 + Hg 2 = Hg. 2 + ? (2 vols.). Ozonised oxygen 
is deozonised when passed through a tube filled with binoxide of manganese, which 
also decomposes peroxide of hydrogen. 

By placing a freshly-scraped stick of phosphorus (scraped under water to avoid 
inflammation) at the bottom of a quart bottle, with enough water to cover half of it, 
and loosely covering the bottle with a glass plate, enough ozone may be accumu- 
lated in a few minutes to be readily recognised by the odour and the iodised starch. 

The water at the bottom of the bottle is found to contain, besides the phos- 
phorous acid formed by the slow oxidation of the phosphorus, some peroxide of 
hydrogen, whence it has been supposed that the formation of ozone is due to the 
decomposition of a molecule of oxygen into electro-negative oxygen, which combines 
with another molecule of oxygen to form ozone, and electro -positive oxygen, which 
combines with a molecule of water to form peroxide of hydrogen. Thus, 

2 + 00 + H 2 = H 2 00 + 2 . 
-+ + 

This view is supported by the circumstance, that peroxide of hydrogen appears 
to be produced in every case where ozone is formed in the presence of water. 

If a few drops of ether be poured into a quart beaker (fig. 49), taking care to 
avoid the vicinity of a flame, and pieces of iodised starch-paper and blue litmus 
paper be suspended upon a glass rod laid across the mouth of the beaker, they 
will be -found unaffected by the mixture of ether vapour and air ; but if a hot glass 
rod be plunged into the beaker, the heated ether vapour will undergo oxidation, 
producing acid vapours, which redden the blue litmus, whilst the formation of 
ozone will be indicated by the blue iodised starch. * 

Ether and essential oils, such as turpentine, slowly absorb oxygen from the air, 

* The oxygen obtained by the action of warm sulphuric acid on binoxide of barium 
resembles ozone in its odour and action on the iodised starch- paper. 



54 



ATMOSPHERIC AIR. 



thus acquiring the property of bleaching indigo and of bluing the mixture of iodide 
of potassium and starch ; hence they were formerly believed to contain ozone, but 

they do not answer to all the tests for thai sub- 
stance. Thus, ozone imparts a blue colour to the 
resin of guaiacum, but the old turpentine or ether 
will not do so. If a little peroxide of hydrogen 
be dissolved in ether, it exhibits the same property 
as the ether which has absorbed oxygen from the 
air, and it is, therefore, sometimes called ' ' ozonic 
ether" The solution of peroxide of hydrogen in 
ether (obtained by shaking the aqueous solution of 
the peroxide with ether) is employed by Dr Day 
for the recognition of blood-stains. Contact with 
blood decomposes peroxide of hydrogen, and the 
■=_ oxygen which is liberated is capable of bluing 
IBEe^ guaiacum resin. Accordingly, if a blood-stain be 
JfP 7 moistened with tincture of guaiacum (a solution of 
the resin in spirit of wine), and afterwards with 
the ethereal solution of peroxide of hydrogen (ozonic 
ether), it acquires an intense blue colour, which may 
be detected, even on a coloured fabric, by pressing a piece of white blotting-paper 
upon it. 

Ozone has attracted much notice, because a minute proportion of the oxygen in 
the atmosphere appears sometimes to be present in this form, and its active pro- 
perties have naturally led to the belief that it must exercise some influence upon 
the sanitary condition of the air This idea is encouraged by the circumstance 
that no indications of ozone can be perceived in crowded cities, where there are 
so many oxidisable substances to consume the active oxygen, whilst the air in the 
open country and at the sea-side does give evidence of its presence. Some chemists 
assert that their experiments have demonstrated the very important fact that a portion 
of the oxygen developed by growing plants is in the ozonised form. 




Fig. 49. 



ATMOSPHEEIC AIR 

50. Atmospheric air consists chiefly of a mixture of nitrogen with, one- 
fifth of its volume of oxygen, and very small proportions of carbonic 
acid and ammonia. Vapour of water is of course always present in the 
atmosphere in varying proportions. Since the atmosphere is the recep- 
tacle for all gaseous emanations, other substances may be discovered in 
it by very minute analysis, but in proportions too small to have any per- 
ceptible influence upon ijbs properties. Thus marsh-gas or light carburetted 
hydrogen, sulphuretted hydrogen, and sulphurous acid, can often be 
traced in it, the two last especially in or near towns. 

Although the proportion of oxygen in the air at a given spot may be 
much diminished, and that of carbonic acid increased, by processes of 
oxidation (such as respiration and combustion) taking place there, the 
operation of wind and of diffusion so rapidly mixes the altered air with 
the immensely greater general mass of the atmosphere, that the variations 
in the composition of air in different places are very slight. Thus it has 
been found that the proportion of oxygen in the air in the centre of Man- 
chester was, at most, only 0*2 per cent, below the average. 

The proportions in which the oxygen and nitrogen are generally pre- ' 
sent in atmospheric air are — 





Volumes. 


Weights. 


Nitrogen, .... 
Oxygen, .... 


79-19 
20-81 


76-99 
23-01 


100-00 


100-00 



ATMOSPHERIC AIR. 



55 




Fig. 50. 



The proportion of aqueous vapour may be stated, on the average, as 1 "4 
per cent, by volume, or 0*87 per cent, by weight of the air. The carbonic 
acid may be generally estimated at 0*04 per cent, by volume, or 0*06 per 
cent, by weight of the air. 

The relative proportions of oxygen and nitrogen in air may be exhibited by sus- 
pending a stick of phosphorus upon a wire stand (A, fig. 50) in a measured volume of 
air confined over water. The cylinder (B) should 
have been previously divided into five equal spaces 
by measuring water into it, and marking each space 
by a thin line of Brunswick black. After a few 
hours, the phosphorus will have combined with the 
whole of the oxygen to form phosphorous acid, which 
is absorbed by the water, leaving four of the spaces 
occupied by nitrogen. 

The same result may be arrived at in a much 
shorter time by burning the phosphorus in the con- 
fined portion of air. 

A fragment of phosphorus, dried by careful pres- 
sure between blotting paper, is placed upon a con- 
venient stand (A, fig. 51) and covered with a tall 
jar, having an opening at the top for the insertion of 
a well-fitting stopper (which should be greased with 
a little lard), and divided into seven parts of equal 
capacity. The jar .should be placed over the stand in such a manner that the water 
may occupy the two lowest spaces into which the jar is divided. The stopper of the 
jar is furnished with a hook, to which a piece 
of brass chain (B) is attached, long enough to 
touch the phosphorus when the stopper is 
inserted. The end of this chain is heated in 
the flame of a lamp, and the stopper tightly 
fixed in its place. On allowing the hot chain 
to touch the phosphorus, it bursts into vivid 
combustion, filling the jar with thick white 
fumes, and covering its sides, for a few moments, 
with white flakes of phosphoric acid. At the 
commencement of the experiment, the water in 
the jar will be depressed, in consequence of the 
expansion of the air, due to the heat produced 
in the burning of the phosphorus, but, pre- 
sently, when the combustion begins to decline, 
the water again rises, and continues to do so 
until it has ascended to the line (C), so as to 
occupy the place of one-fifth of the air employed 
in the experiment. The phosphorus will then have ceased to burn, the white flakes 
upon the sides of the jar will have acquired the appearance of drops of moisture, and 
the fumes will have gradually disappeared, until, in the course of half-an-hour, the 
air remaining in the jar will be as clear and transparent as before, the whole of the 
phosphoric acid having been absorbed by the water. The jar should now be sunk in 
water, so that the latter may attain to the same level without as within the jar. On 
removing the stopper, it will be found that the nitrogen in the jar will no longer 
support the combustion of a taper. 

In the rigidly accurate determination of the relative proportions of oxygen and 
nitrogen in the air, it is, of course, necessary to guard against any error arising from 
the presence of the water, carbonic acid, and ammonia. With this view, Dumas and 
Boussingault, to whom we are chiefly indebted for our exact knowledge of the com- 
position of the air, caused it to pass through a series of tubes (A, fig. 52) containing 
potash, in order to remove the carbonic acid, then through a second series (B), containing 
sulphuric acid, to absorb the ammonia and water ; the purified air then passed through 
a glass tube (C) filled with bright copper heated to redness in a charcoal furnace, 
which removed the whole of the oxygen, and the nitrogen passed into the large globe (N). 

Both the tube (containing the copper) and the globe were carefully exhausted of 
air and accurately weighed before the experiment ; on connecting the globe and the 
tube with the purifying apparatus, and slowly opening the stop-cocks, the pressure 
of the external air caused it to flow through the series of tubes into the globe destined 




56 



ANALYSIS OF AIR. 



to receive the nitrogen. When a considerable quantity of air had passed in, the stop- 
cocks were again closed, and, after cooling, the weight of the globe was accurately 
determined. The difference between this weight and that of the empty globe before 
the experiment, gave the weight of the nitrogen which had entered the globe, but 
this did not represent the whole of the nitrogen contained in the analysed air, for the 




Fig. 52. -Exact analysis of air. 

tube containing the copper had, of course, remained full of nitrogen at the close of 
the experiment. This tube having been weighed, was attached to the air-pump, the 
nitrogen exhausted from it, and the tube again weighed ; the difference between the 
two weighings furnished the weight of the nitrogen remaining in the tube, and was 
added to the weight of that received in the globe. The oxygen was represented by 
the increase in the weight of the exhausted tube containing the copper, which was 
partially converted into oxide of copper, by combining with the oxygen of the air 
passed through it. 

The calculation of the result of the analysis is here exemplified : — 

"Weight of Grains. 

Globe (N) with nitrogen (at the conclusion), . . . 3076 
Exhausted globe (at the commencement), . . . 3000 



Nitrogen received into the globe, 

Tube (C) with residual nitrogen (at the conclusion), 
Exhausted tube (at the conclusion), 

Nitrogen remaining in the tube, 
Add nitrogen received into the globe, 

• Total nitrogen in the air analysed, 



76 

2574 
2573 

1 

76 

77 



Exhausted tube (C) with oxidised copper (at the conclusion), 
,, ,, metallic copper (at the commencement), 

Oxygen in the air analysed, . . . . 



2573 

2550 

23 



The ratio of the nitrogen to> the oxygen, therefore, is that of 23 N : 77 O, or 1 N : 
3 '347 O. 100 parts by weight of the air purified from 
water, carbonic acid, and ammonia, contain 77 parts of 
nitrogen and 23 parts of oxygen. 

51. The nitrogen remaining after the removal 
of the oxygen from air in the above experiments 
was so called on account of its presence in nitre 
(saltpetre KN0 3 ). In physical properties it re- 
sembles oxygen, but is somewhat lighter than 
that gas, its specific gravity being 0*9 7 13. 

This difference in the specific gravities of the two gases 
is well exhibited by the arrangement shown in fig. . 
53. A jar of oxygen (O) is closed with a glass plate, and 
placed upon the table. Ajar of nitrogen (N), also closed 
with a glass plate, is placed over it, so that the two 
gases may come in contact when the glass plates are 
removed. The nitrogen will float for some seconds 
above the oxygen, and if a lighted taper be quickly 
introduced through the neck of the upper jar, it will be 
extinguished in passing through the nitrogen, and will 
be rekindled brilliantly when it reaches the oxygen in 
Fig. 53. the lower jar. 




DIALYSIS OF AIR. 



7 



It might at first sight appear surprising that oxygen and nitrogen, 
though of different specific gravities, should exist in uniform proportions 
in all parts of the atmosphere, unless in a state of chemical combination ; 
but an acquaintance with the property of diffusion (see 13) possessed by 
gases teaches us that gases ivill mix with each other in opposition to gravi- 
tation, and when mixed loill always remain so. 

It was shown by Graham that a partial separation of the nitrogen and oxygen in 
air may be effected, on the same principle as that of hydrogen and oxygen at page 
18, by taking advantage of the difference in their rates of diffusion. He devised, 
however, a more convenient process, founded upon the dialytic passage of the gases ' 
through caoutchouc, which he ascribed to the absorption of the gas by the solid 
material upon one side, and its escape on the other. 

A bag (a, fig. 54) is made of a fabric composed of a layer of caoutchouc between 
two layers of silk, such as that employed for waterproof garments ; a piece of carpet 
is placed inside the bag to keep the sides apart, 
and the edges of the bag are made perfectly air- 
tight with solution of caoutchouc. To main- 
tain a vacuum within the bag, it is supported 
by the rod v, and attached to SprengeVs air- 
pump, in which a stream of mercury, allowed 
to flow from a funnel (/) down a tube (c) six 
feet long, draws the air out of the bag, through 
a lateral tube (h), until all the air is exhausted, 
which is indicated by the barometer tube b, the 
lower end of which dips into a cistern of mer- 
, cury. When the mercury in this tube stands 
! at almost exactly the same height as the stan- 
dard barometer, the exhaustion is complete. 
If a test-tube (d) filled with mercury be now 
inverted over the end of the long tube c, which 
is bent upwards for that purpose, the bubbles 
of air which are drawn through the sides of the 
pacuous bag, and carried down the long tube 
by the little pistons of liquid mercury as they 
all, will pass up into the test-tube ; when the 
atter is filled with the gas, its mouth is closed 
rith the thumb, withdrawn from the mercury, 
ind a match with a spark at the end inserted, 
'hen the spark will burst out into flame, 
lowing that the specimen of air collected is 

mch richer in oxygen than ordinary atmo- 

meric air. The overflow tube g delivers 

le mercury which is to be returned to the 

iinel /. 

The dialytic passage of oxygen through 

Cmtchouc into a vacuum is twice as rapid as 

tit of nitrogen, so that the air collected in the 

tie contains twice as much oxygen as the 

e'ernal air. 
pis dialytic passage of gases through solids is quite unconnected with the diffusi- 

b&y of the gases, and appears to depend rather upon the chemical nature of the 

g*and of the solid. It is thus connected with the occlusion of gases by solids, 

eiaplified in the case of palladium and hydrogen at page 38. It is in consequence 

ofjiis dialytic passage that tubes of iron or platinum, which are quite impermeable 

bjydrogen at the ordinary temperature, will allow it to pass rapidly through their 

wis at high temperatures. 

hat air is simply a mechanical mixture of its component gases is amply 
pr^ed by the circumstance that it possesses all the properties which 
wdd be predicted for a mixture of these gases in such proportions ; 
whst the essential feature of a chemical compound is, that its properties 
carpt be foreseen from those of its constituents. 




54. — Sprengel's pump. 
Dialysis of air. 



58 CARBON. • 

The absence of active chemical properties is a very striking feature 
of nitrogen, and admirably adapts it for its function of diluting the 
oxygen in the atmosphere. 

The chemical relations of air to animals and plants will be more appro- 
priately discussed hereafter. (See Carbonic Acid, Ammonia.) 



CAKBON. 

C = 12 parts by weight.* 

52. This element is especially remarkable for its uniform presence in 
organic substances. The ordinary laboratory test by which the chemist 
decides whether a substance under examination is of organic origin, con- 
sists in heating it with limited access of air, and observing whether any 
blackening from separation of carbon {carbonisation) ensues. 

Few elements are capable of assuming so many different aspects as 
carbon. It is met with transparent and colourless in the diamond, opaque, 
black, and quasi-metallic in graphite or black lead, velvety and porous in 
wood-charcoal, and under new conditions in anthracite, coJce, and gas- 
carbon. 

In nature, free carbon may be said to occur in the forms of diamond, 
graphite, and anthracite (the other varieties of coal containing considerable 
proportions of other elements). 

Apart from its great beauty and rarity, the diamond possesses a special 
interest in chemical eyes, from its having perplexed philosophers up to 
the middle of the last century, notwithstanding the simplicity of the ex- 
periments required to demonstrate its true nature. The first inkling of it 
appears to have been obtained by Newton, when he perceived its grea 
power of refracting light, and thence inferred that, like other bodie 
possessing that property in a high degree, it would prove to be con 
bustible (" an unctuous substance coagulated "). When this predictio 
was verified, the burning of diamonds was exhibited as a marvelloi 
experiment, but no accurate observations appear to have been made ti 
1772, when Lavoisier ascertained, by burning diamonds suspended in tb 
focus of a burning-glass, in a confined portion of oxygen, that they we 
entirely converted into carbonic acid gas. In more recent times tls 
experiment has been repeated with the utmost precaution, and te 
diamond has been clearly demonstrated to consist of carbon in a crysii- 
lised state. 

A still more important result of this experiment was the exact determinatiorof 
the composition of carbonic acid, without which it would not be possible to ascer'in 
exactly the proportion of carbon in any of its numerous compounds, since it is alvys 
weighed in that form. 

The most accurate experiments upon the synthesis of carbonic acid have been >n- 
ducted with the arrangement represented in fig. 55. 

Within the procelain tube A, which is heated to redness in a charcoal fire/as 
placed a little platinum tray, accurately weighed, and containing a weighed quaity 
of fragments of diamond. One end of the tube was connected with a gas-hold B, 
containing oxygen which was thoroughly purified by passing through the tu C, 
containing potash (to absorb any carbonic acid and chlorine which it might con-in), 
and dried by passing over pumice soaked with concentrated sulphuric acid in land 
E. To the other end of the porcelain tube A, there was attached a glass tu F, 
also heated in a furnace, and containing oxide of copper, to convert into caonic 

* The volume occupied by carbon in the form of vapour is not known, its vapoutever 
having been obtained in a measurable form. 



SYNTHESIS OF CARBONIC ACID. 



59 



acid any carbonic oxide which might have been formed in the combustion of the 
diamond. The carbonic acid was then passed over pumice soaked with sulphuric 
acid in G, to remove any traces of moisture, and afterwards into a weighed bulb- 
apparatus H, containing solution of potash, and two weighed tubes I, K, containing, 




Exact synthesis of carbonic acid. 



respectively, solid hydrate of potash, and sulphuric acid on pumice, to guard against 
the escape of aqueous vapour taken up by the excess of oxygen in its passage 
through the bulbs H. The increase of weight in H, I, K, represented the carbonic 
acid formed in the combustion of an amount of diamond, indicated by the loss of 
weight suffered by the platinum tray, and the difference between the diamond con- 
sumed and the carbonic acid formed would express the amount of oxygen which had 




Fig. 56. 

combined with the carbon. A large number of experiments conducted in this manner, 
both with diamond and graphite, showed that 12 parts of carbon furnished 44 parts 
of carbonic acid, and consumed, therefore, 32 parts of oxygen. 

The ordinary mode of exhibiting the combustion of the diamond on the lecture 




60 COMBUSTION OF DIAMOND. 

table, consists in suspending it within a double loop of platinum wire attached to an 
iron wire passing through a deflagrating-collar, and heating it in a jet of oxygen 
sent through a gas or spirit flame (fig. 56). As soon as it has attained a white heat, 
the diamond is plunged into a globe of oxygen, and after burning for a few seconds, 
it is withdrawn, and a little lime-water is shaken in the globe to produce the milky 
deposit of carbonate of lime. It not unfrecpiently happens that the blowpipe flame 
fuses the platinum wire, and the diamond drops out before it can be immersed in the 
oxygen. A more convenient arrangement is shown in fig. 57. 
The diamond is supported in a short helix of platinum wire A, 
which is attached to the copper wires B B, passing through the 
cork C, and connected with the terminal wires of a Grove's 
battery of five or six cells. The globe having been filled with 
oxygen by passing the gas down into it till a match indicates 
that the excess of oxygen is streaming out of the globe, the cork 
is inserted, and the wires connected with the battery. "When the 
heat developed in the platinum coil, by the passage of the 
Fig. 57. current, has raised the diamond to a full red heat, the connexion 

with the battery may be interrupted, and the diamond will con- 
tinue to burn with steady and intense brilliancy. 

To an observer unacquainted with the satisfactory nature of this de- 
monstration, it would appear incredible that the transparent diamond, so 
resplendent as to have been reputed to emit light, should be identical in 
its chemical composition with graphite (plumbago or black lead) from 
which, in external appearance, it differs so widely. For this difference is 
not confined to their colour ; in crystalline form they are not in the least 
alike, the diamond occurring generally in octahedral crystals, while gra- 
phite is found either in amorphous masses (that is, having no definite 
crystalline form), or in six-sided plates which are not geometrically allied 
with the form assumed by the diamond. Carbon, therefore, is dimorphous, 
or occurs in two distinct crystalline forms. Even in weight, diamond and 
graphite are very dissimilar, the former having an average specific gravity 
of 3 5, and the latter of 2*3. Again, a crystal of diamond is the hardest 
of all substances, whence it is used for cutting and for writing upon glass, 
but a mass of graphite is soft and easily cut with a knife. The diamond 
is a non-conductor of electricity, but the conducting power of graphite 
renders it useful in the electrotype process. 

Diamonds are chiefly obtained from Golconda, Borneo, and the Brazils. 
They usually occur in sandstone rock or in mica slate. The hardness of 
the diamond renders it necessary to employ diamond-dust for the purpose 
of cutting and polishing it, which is effected with .the aid of a revolving 
disk of steel, to the surface of which the diamond-dust is applied in the 
form of a paste made with oil. The crystal in its natural state is best 
fitted for the purpose of the glazier, for its edges are usually somewhat 
curved, and the angle formed by these cuts the glass deeply, while the 
angle formed by straight edges, like those of an ordinary jeweller's dia- 
mond, is only adapted for scratching or writing upon glass. Drills with 
diamond points have been employed in tunnelling through bard rocks. 
The diamond-dust used for polishing, &c, is obtained from a dark amor- 
phous diamond found at Bahia in the Brazils; 1000 ounces annually are 
said to have been occasionally obtained from this source. When burnt, 
the diamond always leaves a minute proportion of ash of a yellowish 
colour in which silica and oxide of iron have been detected. A genuine 
diamond may be known by its combining the three qualities of extreme 
hardness, enabling it to scratch hardened steel, high specific gravity 
(3*53), and insolubility in hydrofluoric acid. 

Although the diamond, when preserved from contact with the air, may 



LAMP BLACK — WOOD CHARCOAL. 61 

be heated very strongly in a furnace, without suffering any change, it is 
not proof against the intense heat of the discharge taking place between 
two carbon points attached to the terminal wires of a powerful galvanic 
battery. If the experiment be performed in a vessel exhausted of air, the 
diamond becomes converted into a black coke-like mass which closely re- 
sembles graphite in its properties. 

Graphite always leaves more ash than the diamond, consisting chiefly 
of the oxides of iron and manganese, with particles of quartz, and some- 
times titanic acid. The purest specimens are those of compact amor- 
phous graphite from Borrowdale in Cumberland ; an inferior variety, im- 
ported from Ceylon, is crystalline, being composed of hexagonal plates. 
Graphite is obtained artificially in the manufacture of cast iron : in some 
cases, a portion of the carbon of the cast iron separates in cooling, in the 
form of crystalline scales of graphite, technically called kish. In the 
grey variety of cast iron these scales of graphite are diffused through the 
mass of the metal, and are left undissolved when the iron is dissolved by 
an acid. 

Graphite is far more useful than the diamond, for, in addition to its 
application in black lead pencils, and for covering the surface of iron in 
order to protect it from rust, it is largely employed, in admixture with 
clay, for the fabrication of the black lead crucibles or blue pois, as they 
are commonly called, which are so valuable to the metallurgist, for their 
power of resisting high temperatures. Graphite is also sometimes em- 
ployed for lubricating, to diminish friction in machinery, and for facing 
or imparting a fine glazed surface to gunpowder. 

(Anthracite and the other varieties of coal will be described in a sepa- 
rate section.) 

53. Several varieties of carbon, obtained by artificial processes, are 
employed in the arts. The most important of these are lamp black, icood 
charcoal and animal charcoal. 

Lamp black approaches more nearly in composition to pure carbon than 
either of the others, and is the soot obtained from the imperfect combus- 
tion of resinous and tarry matters (or of highly bituminous coal), from 
which source it derives the small quantities of resin, of nitrogen, and sul- 
phur which it contains. The uses of this substance, as an ingredient of 
pigments, of printing, ink, and of blacking, depend evidently more upon 
its black colour than upon its chemical properties. 

Wood charcoal presents more features which arrest the attention of the 
chemist, as well on account of its specific properties, as of the influence 
exercised by the method adopted for obtaining it, upon its fitness for the 
particular purpose which it may be destined to serve. 

If a piece of wood be heated in an ordinary fire, it is speedily con- 
sumed, with the exception of a grey ash consisting of the incombustible 
mineral substances which it contained ; if the experiment were performed 
in such a manner that the products of combustion of the wood could be 
collected, these would be found to consist of carbonic acid and water ; 
woody fibre is composed of carbon, hydrogen, and oxygen (C 6 H 10 O 5 ), 
and when it is burnt, the oxygen, in conjunction with more oxygen de- 
rived from the air, converts the carbon and hydrogen into carbonic acid 
and water. But if the wood be heated in a glass tube, closed at one end, 
it will be found impossible to reduce it, as before, to an ash, for a mass of 
charcoal will remain, having the same form as that of the piece of wood ; 



62 



PREPARATION OF CHARCOAL. 



in this case, the oxygen of the air not having been allowed free access to 
the wood, no true combustion has taken place, but the wood has under- 
gone destructive distillation, that is, its elements have arranged them- 
selves, under the influence of the high temperature, into different forms 
of combination, for the most part simpler in their chemical composition than 
the wood itself, and capable, unlike the wood, of enduring that temperature 
without decomposition ; thus, it is merely an exchange of an unstable for 
a stable equilibrium of the particles of matter composing the wood. 

(Def. — Destructive distillation is the resolution of a complex substance 
into simpler forms under the influence of heat, out of contact with air.) 

The vapours issuing from the mouth of the tube will be found acid 
to blue litmus paper ; they have a peculiar odour, and readily take fire 
on contact with flame. These will be more particularly noticed here- 
after, as they contain some very useful substances. The charcoal which 
is left is not pure carbon, but contains considerable quantities of oxygen 
and hydrogen, with a little nitrogen, and the mineral matter or ash of 
the wood. 

When the charcoal is to be used for fuel, it is generally prepared by 
a process in which the heat developed by the combustion of a portion 
of the wood is made to effect the charring of the rest. With this view 
the billets of wood are built up into a heap (fig. 58) around stakes driven 

into the ground, a passage 
being left so that the heap 
may be kindled in the centre. 
This mound of wood, which 
is generally from 30 to 40 feet 
in diameter, is closely covered 
with turf and sand, except for 
a few inches around the base, 
where it is left uncovered to 
give vent to the vapour of 
water expelled from the wood 
in the first stage of the process. 
When the heap has been kindled in the centre, the passage left for this 
purpose is carefully closed up After the combustion has proceeded for 

some time, and it is judged that 
the wood is perfectly dried, the 
open space at the base is also 
closed, and the heap left to 
smoulder for three or four weeks, 
when the wood is perfectly car- 
bonised. 

Upon an average, 22 parts of 
charcoal are obtained by this pro- 
cess from 100 of wood. 

A far more economical process 
for preparing charcoal from wood 
consists in heating it in an iron 
case or slip (F, fig. 59) placed in 
an iron retort A, from which the 
gases and vapours are conducted 
by the pipe L into the furnace B, where they are consumed. 

On the small scale, the operation may be conducted in a glass 




Charcoal heap. 




Fig. 59.— Charcoal retort. 



ABSORPTION OF GASES BY CHARCOAL. 



retort, as shown in fig. 60, where the water, tar, and naphtha are 
deposited in the globular receiver, and the inflammable gases are collected 
over water. 

The infusibility of the charcoal left by wood accounts for its 
very great porosity, upon which some of its most remarkable and 
useful properties depend. The application of charcoal for the purpose 
of " sweetening" fish and other food in a state of incipient putre- 
faction has long been practised, and more recently charcoal has 
been employed for deodorising all kinds of putrefying and offensive 
animal or vegetable matter. This property of charcoal depends upon 
its power of absorbing into its pores very considerable quantities of 
the gases, especially of those which are easily absorbed by water. Thus, 
one cubic inch of charcoal is capable of absorbing about 100 cubic 
inches of ammonia gas and 50 cubic inches of sulphuretted hydrogen, 
both which are conspicuous among the offensive results of putrefac- 
tion. This condensation of gases by charcoal is a mechanical effect, and 
does not involve a chemical 
combination of the charcoal 
with the gas ; it is exhibited 
most powerfully by char- 
coal which has been re- 
cently heated to redness in 
a closed vessel, and cooled 
out of contact with air by 
plunging it under mercury. 
Eventually the offensive 
gases absorbed by the char- 
coal are chemically acted on 
by the oxygen of the air in its pores. A cubic inch of wood charcoal absorbs 
nearly 10 cubic inches of oxygen, and when the charcoal containing the gas 
thus condensed is presented to another gas which is capable of undergoing 
oxidation, this latter gas is oxidised and converted into inodorous pro- 
ducts. Thus, if charcoal be exposed to the action of air containing sul- 
phuretted hydrogen gas, it condenses within its -pores both this gas and 




Fig. 60.— Distillation of wood. 





Fig. 61. 



Fig. 62. 



the atmospheric oxygen, which then converts the hydrogen into water 
(H 2 0) and the sulphur into sulphuric acid (S0 3 ). 

The great porosity of wood charcoal is strikingly exhibited by attaching a piece of 
lead to a stick of charcoal (fig. 61), so as to sink it in a cylinder of water, which is 



64 



DE-ODORISING AND DECOLORISING BY CHARCOAL. 



then placed under the receiver of the air-pump. On exhausting the air, innumerable 
bubbles will start from the pores of the charcoal, causing brisk effervescence. If a 
glass tube 16 or 18 inches long be thoroughly filled with ammonia gas (fig. 62), sup- 
ported in a trough containing mercury, and a small stick of recently calcined char- 
coal introduced through the mercury into the tube, the charcoal will absorb the 
ammonia so rapidly that the mercury will soon be forced up and fill the tube, 
carrying the charcoal up with it. On removing the charcoal, and placing it upon 
the hand, a sensation of cold will be perceived from the rapid escape of ammonia, 
perceptible by its odour. 

By exposing a fragment of recently calcined wood-charcoal under a jar filled with 
hydrosulphuric acid gas for a few minutes, so that it may become saturated with 
the gas, and then covering it with a jar of oxygen, the latter gas will act upon 
the former with such energy that the charcoal will burst into vivid combustion. 
The jar must not be closed air-tight at the bottom, or the sudden expansion may 
burst it. Charcoal in powder exposed in a porcelain crucible may also be em- 
ployed in the same waj\ It should be pretty strongly heated in the covered cru- 
cible, and allowed to become nearly cool before being exposed to the hydrosulphuric 
acid. 

Charcoal prepared from hard woods absorbs the largest volume of gas. Thus 
logwood charcoal has been found to absorb 111 times its volume of ammoniacal 
gas. Charcoal made from the shell of the cocoa-nut is even more absorbent, 
although its pores are quite invisible, and its fracture exhibits a semi-metallic lustre. 

As the gases which are evolved in putrefaction are of a poisonous cha- 
racter, the power of wood charcoal to remove them acquires great practical 
importance, and is applied in very many cases ; the charcoal in coarse 
powder is thickly .strewn over matters from which the effluvium proceeds, 
or is exposed in shallow trays to the air to be sweetened, as in the wards 
of hospitals, &c. It has even been placed in a flat box of wire gauze to 
be fixed as a ventilator before a window through which the contaminated 
air might have access, and respirators constructed on the same principle 
have been found to afford protection against poisonous gases and vapours. 
The ventilating openings of sewers in the streets are also fitted with 
cases containing charcoal for the same purpose. Water is often filtered 
through charcoal in order to free it from the noxious and putrescent 
organic matters which it sometimes contains. For all such uses the char- 
coal should have been recently heated to redness in a covered vessel in 

order to expel the moisture which it at- 
tracts when exposed to the air ; and the 
charcoal which has lost its power of absorp- 
tion will be found to regain it in great 
measure when heated to redness. 

This power of absorption which char- 
coal possesses is not confined to gases, 
for many liquid and solid substances, 
are capable of being removed by that 
agent from their solution in water. This 
is most readily traced in the case of 
substances which impart a colour to the 
solution, such colour being often removed 
by the charcoal ; if port wine or infusion of 
logwood be shaken with powdered charcoal 
(especially if the latter has been recently 
heated to redness in a closed crucible), the 
liquid, when filtered through blotting 
paper (fig. 63), will be found to have lost its colour ; the colouring mat- 
ter, however, seems merely to have adhered to the charcoal, for it may 
be extracted from the latter by treatment with a weak alkaline liquid. 




Fig. 63.— Filtration. 



CHEMICAL RELATIONS OF CARBON. 65 

The decolorising power of wood charcoal is very feeble in comparison 
with that possessed by hone-black or animal charcoal, which is 
obtained by heating bones in vessels from which the air is ex- 
cluded. Bones are composed of about one-third of animal and two- 
thirds of mineral substances, the latter including phosphate of lime, 
which amounts to more than half the weight of the bone, and a little 
carbonate of lime. When bone is heated, as in a retort, so that air is 
not allowed to have free access to it, the animal matter undergoes 
destructive distillation, its elements — carbon, hydrogen, nitrogen, and 
oxygen — assuming other forms, the greater part of the three last elements, 
together with a portion of the carbon, escaping in different gaseous and 
vaporous products, while a considerable proportion of the carbon remains 
behind, intimately mixed with the earthy ingredients of the bone, and 
constituting the substance known as animal charcoal. The great differ- 
ence between the products of the destructive distillation of bone and of 
wood deserves a passing notice. If a fragment of bone or a shaving of 
horn be heated in a glass tube closed at one end, the vapours which are 
evolved will be found strongly alkaline to test-papers, while those fur- 
nished by the wood were acid ; this difference is to be ascribed mainly 
to the presence of nitrogen in the bone, wood being nearly free from that 
element ; it will be found to hold good as a general rule, that the results 
of the destructive distillation of animal and vegetable matters containing 
much nitrogen are alkaline, from the presence of ammonia (NH 3 ) and 
similar compounds, while those furnished by non-nitrogenised substances 
possess acid characters : the peculiar odour which is emitted by the heated 
bone is characteristic, and affords us a test by which to distinguish 
roughly between nitrogenised and non-nitrogenised bodies. 

An examination of the charred mass remaining as the ultimate result 
of the action of heat upon bone, shows it to contain much less carbon 
than that furnished by v> ood, for the bone-charcoal contains nearly nine- 
tenths of its weight of phosphate (with a little carbonate) of lime ; the 
consequence of the presence of so large an amount of earthy matter must 
be to extend the particles of carbon over a larger space, and thus to ex- 
pose a greater surface for the adhesion of colouring matters, &c. This 
may partly help to explain the very great superiority of bone-black to 
wood charcoal as a decolorising agent, and the explanation derives support 
from the circumstance, that when animal charcoal is deprived of its earthy 
matter, for chemical uses, by washing with hydrochloric acid, its decolor- 
ising power is very considerably reduced. The application of this variety 
of charcoal is not confined to the chemical laboratory, but extends to 
manufacturing processes. The sugar-refiner decolorises his syrup by filter- 
ing it through a layer of animal charcoal, and the distiller employs char- 
coal to remove the empyreumatic oils with which distilled spirits are 
frequently contaminated. 

Carbon is remarkable, among elementary bodies, for its indisposition to 
enter directly into combination with the other elements, whence it follows 
that most of the compounds of carbon have to be obtained by indirect 
processes. This element appears, indeed, to be incapable of uniting with 
any other at the ordinary temperature, and this circumstance is occasion- 
ally turned to useful account, as when the ends of wooden stakes are 
charred before being plunged into the earth, when the action of the 
atmospheric oxygen, which, in the presence of moisture, would be very 
active in effecting the decay of the wood, is resisted by the charcoal into 



66 FORMATION OF COAL. 

which, the external layer has been converted. The employment of black 
lead to protect metallic surfaces from rust is another application of 
the same principle. At a high temperature, however, carbon combines 
readily with oxygen, sulphur, and with some of the metals, and at a 
very high temperature, even with hydrogen. The tendency of carbon to 
combine with oxygen under the influence of heat, is shown when a piece 
of charcoal is strongly heated at one point, when the carbon at this point 
at once combines with the oxygen of the surrounding air (forming car- 
bonic acid), and the heat developed by this combustion raises the neigh- 
bouring particles of carbon to the temperature at which the element unites 
with oxygen, and thus the combustion is gradually propagated throughout 
the mass, which is ultimately converted entirely into carbonic acid gas, 
nothing remaining but the white ash, composed of the mineral substances 
derived from the wood employed for preparing the charcoal. It is worthy 
of remark, that if charcoal had been a better conductor of heat, it would 
not have been so easily kindled, since the heat applied to any point of 
the mass would have been rapidly diffused over its whole bulk, and this 
point could not have attained the high temperature requisite for its 
ignition, until the whole mass had been heated nearly to the same degree; 
this is actually found to be the case in charcoal which has been very 
strongly heated (out of contact with air), when its conducting power is 
greatly improved, and it kindles with very great difficulty. The calorific 
value of carbon is represented by the number 8080, that is, 1 gr. of car- 
bon, when burnt so as to form carbonic acid, is capable of raising 8080 
grs. of water from 0° C. to 1° C. 

A given weight of charcoal will produce twice as much available heat 
as an equal weight of wood, since the former contains more actual fuel 
and less oxygen, and much of the heat evolved by the wood is absorbed 
or rendered latent in the steam and other vapours which are produced by 
the action of heat upon it. The attraction possessed by carbon for oxygen 
at a high temperature is turned to account in metallurgic operations, when 
coal and charcoal are employed for extracting the metals from their com- 
pounds with oxygen.* 

The unchangeable solidity of carbon is another remarkable feature. It 
is stated that some approach has been made, at extremely high tempera- 
tures, to the fusion and vaporisation of carbon, but it cannot be said to 
have been fairly established that this element is able to exist in any other 
than the solid form. Nor can any substance be found by the aid of 
which carbon may be brought into the liquid form by the process of 
solution, for although charcoal gradually disappears when boiled with 
sulphuric and nitric acids, it does not undergo a simple solution, but is 
converted, as will be seen hereafter, into carbonic acid. 

54. Coal. — The various substances which are classed together under 
the name of coal are characterised by the presence of carbon as a largely 
predominant constituent, associated with smaller quantities of hydrogen, 
oxygen, nitrogen, sulphur, and certain mineral matters' which compose the 
ash. Coal appears to have been formed by a peculiar decomposition or 
fermentation of buried vegetable matter, resulting in the separation of a 
large proportion of its hydrogen in the form of marsh-gas (CH 4 ), and 

* Easily reducible oxides, such as oxide of lead, give carbonic acid when heated with 
charcoal; 2PbO + C = Pb 2 + C0 2 , 1 mt oxides which are not easily reducible, such as 
oxide of zinc, give carbonic oxide ; ZnO + C = CO + Zn. 



COMBUSTION OF COAL. 67 

similar compounds, and of its oxygen in the form of carbonic acid (C0 2 ), 
the carbon accumulating in the residue. Thus, cellulose (C 6 H 10 O 5 ), which 
constitutes the bulk of woody fibre, might be imagined to decompose 
according to the equation 2C 6 H 10 O 5 = 5CH 4 + 5C0 2 + C 2 , and the 
occurrence of marsh-gas, and of the petroleum hydrocarbons of similar 
composition, as well as of carbonic acid, in connection with deposits of 
coal, supports this account of its formation. Marsh-gas arid carbonic 
acid are the ordinary products of the fermentation of vegetable matter, 
and a spontaneous carbonisation is often witnessed in the " heating " of 
damp hay. But just as the action of heat upon wood produces a charcoal 
containing small quantities of the other organic elements, so the carbon- 
ising process by which the plants have been transformed into coal, has 
left behind some of the hydrogen, oxygen, and nitrogen ; the last, as well 
probably as a little of the sulphur, having been derived from the vegetable 
albumen and similar substances which are always present in plants. The 
chief part of the sulphur is generally present in the form of iron pyrites, 
derived from some extraneous source. The examination of a peat- bog is 
very instructive with reference to the formation of coal, as affording ex- 
amples of vegetable matter in every stage of decomposition, from that in 
which the organised structure is still clearly visible, to the black carbon- 
aceous mass which only requires consolidation by pressure in order to 
resemble a true coal. 

The three principal varieties of coal — lignite, bituminous coal, and an- 
thracite — present us with the material in different stages of carbonisation; 
the lignite, or brown coal, presenting indications of organised structure, 
and containing considerable proportions of hydrogen and oxygen, while 
anthracite often contains little else than carbon and the mineral matter or 
ash. The following table shows the progressive diminution in the propor- 
tions of hydrogen and oxygen in the passage from wood to anthracite : — 





Carbon. 


Hydrogen. 


Oxygen 


Wood, 


100 


12-18 


83-07 


Peat, . 


100 


9-85 


55-67 


Lignite, 


100 


8-37 


42-42 


Bituminous coal, 


100 


612 


2123 


Anthracite, . 


100 


2-84 


1-74 



The combustion of coal is a somewhat complex process, in consequence 
of the re-arrangement which its elements undergo when the coal is sub- 
jected to the action of heat. 

As soon as a flame is applied to kindle the coal, the heated portion 
undergoes destructive distillation, evolving various combustible gases and 
vapours, which take fire and convey the heat to remoter portions of the 
coal. Whilst the elements of the exterior portion of coal are undergoing 
combustion, the heat thus evolved is submitting the interior of the mass 
to destructive distillation, resulting in the production of various com- 
pounds of carbon and hydrogen. Some of these products, such as marsh - 
gas (CH 4 ) and olefiant gas (C 2 H 4 ), burn without smoke ; while others, 
like benzole (C 6 H 6 ) and naphthaline (C 10 H 8 ), which contain a very large 
proportion of carbon, undergo partial combustion, and a considerable 
quantity of carbon, not meeting with enough heated oxygen in the vicinity 
to burn it entirely, escapes in a very finely divided state as smoke or 
soot, which is deposited in the chimney, mixed with a little carbonate of 
ammonia, and small quantities of other products of the distillation of 
coal. When the gas has been expelled from the coal, there remains a 



68 



VAKIETIES OF COAL. 



mass of coke or cinder, which burns with a steady glow until the whole 
of its carbon is consumed, and leaves an ash, consisting of the mineral 
substances present in the coal. The final results of the perfect combus- 
tion of coal would be carbonic acid (C0 2 ), water (H 2 0), nitrogen, a little 
sulphurous acid (S0 2 ), and ash. The production of smoke in a furnace 
supplied with coal may be prevented by charging the coal in small 
quantities at a time in front of the fire, so that the highly carbonaceous 
vapours must come in contact with a large volume of heated air before 
reaching the chimney. In arrangements for consuming the smoke, hot 
air is judiciously admitted at the back of the fire, in order to meet and 
consume the heated carbonaceous particles before they pass into the 
chimney. 

The difference in the composition of the several varieties of coal gives 
rise to a great difference in their mode of burning. 

The following table exhibits the composition of representative speci- 
mens of the four principal varieties : — 



Composition of Coal. 





Lignite. 


Coal. 


Wigan Canncl. 


Anthracite 


Carbon, 


66'32 


78-57 


80-06 


90-39 


Hydrogen, 


5-63 


5-29 


5-53 


3-28 


Nitrogen, 


0-56 


1-84 


2-12 


0-83 


Oxygen, 


22-86 


12-88 


8-09 


2-98 


Sulphur, 


2-36 


0'39 


1-50 


0-91 


Ash,* . 


2-27 


1-03 


2-70 


1-61 



100-00 



100-00 



100-00 



100-00 



The lignites furnish a much larger quantity of gas under the action of 
heat, and therefore burn with more flame than the other varieties, 
leaving a coke which retains the form of the original coal ; while bitumi- 
nous coal softens and cakes together, — a useful property, since it allows 
even the dust of such coal to be burnt, if the fire be judiciously managed. 
Anthracite (stone coal or Welsh coal) is much less easily combustible 
than either of the others, and since it yields but little gas when heated, 
it usually burns with little flame or smoke. This variety of coal is so 
compact that it will not usually burn in ordinary grates, but is much 
employed for furnaces. 

55. Carbon is capable of combining with oxygen in two proportions, 
forming the compounds known as carbonic oxide and carbonic acid, the 
composition of which is shown in the following table : — 



Oxides of Carbon. 






Carbonic oxide, . . CO, 
Carbonic acid, . . C0 2 , 


Parts by weight. 


c 

12 
12 



16 
32 



The ash of coal consists chiefly of silica, alumina, and peroxide of iron. 



NATURAL SOURCES OF CARBONIC ACID. 69 

Carbonic Acid. 

C0 2 = 44 parts by weight = 2 vols. 

56. It has been already mentioned that carbonic acid is a component 
of the atmosphere, which usually contains about four volumes of carbonic 
acid in 10,000 volumes of air. This carbonic acid is chiefly formed by 
the operation of the atmospheric oxygen in supporting combustion and 
respiration. 

All substances used as fuel contain a large proportion of carbon, which, 
in the act of combustion, combines with the oxygen, and escapes into the 
atmosphere in the form of carbonic acid. 

In the process of respiration, the carbonic acid is formed from the 
carbon contained in the different portions of -the animal frame to which 
oxygen is conveyed by the blood, having been taken up by the latter in 
passing through the lungs, where it gives out, in exchange for the oxygen, 
a quantity of carbonic acid produced by the union of a former supply of 
oxygen with the carbon of the different organs to which the blood is 
supplied, and which, as they are constantly corroded and destroyed by 
this oxidising action of the blood, are repaired by the supply of food taken 
into the body. This conversion of the carbon of the organs into carbonic 
acid will be again referred to ; it will be at once evident that it must be 
concerned in the maintenance of the animal heat. 

The leaves of plants, under the influence of light, have the power of 
decomposing the carbonic acid of the atmosphere, the carbon of which is 
applied to the production of vegetable compounds forming portions of the 
organism of the plant, and when this dies, the carbon is restored, after 
a lapse of time more or less considerable, to the atmosphere, in the same 
form, namely, that of carbonic acid, in which it originally existed there. 
If the plant should have been consumed as food by animals, its carbon 
will have been eventually converted into carbonic acid by respiration ; 
the use of the plant as fuel, either soon after its death (wood), or after 
the lapse of time has converted it into coal, will also consign its carbon 
to the air in the form of carbonic acid. Even if the plant be left to decay, 
this process involves a slow conversion of its carbon into carbonic acid 
by the oxygen of the air.* 

Putrefaction and fermentation are also very important processes con- 
cerned in restoring to the air, in the form of carbonic acid, the carbon 
contained in dead vegetable and animal matter. Although, in a popular 
sense, these two processes are distinct, yet their chemical operation is of 
the same kind, consisting in the resolution of a complex substance into 
simpler forms, produced by contact with some other substance in a state of 
chemical change. The discussion of the true nature of the process (which 
is even now somewhat obscure) would be premature at this stage, and it 
will suffice for the present to state that carbonic acid is one of the simpler 
forms into which the carbon is converted by the metamorphosis which 
ensues so quickly upon the death of animals and vegetables. 

* In the dark, according to Boussingault, plants evolve carbonic acid. He found that 
a square metre (39*37 inches square) of oleander leaves decomposed, in sunlight, on an 
average, 1-108 litre (67 '6 cubic inches) of carbonic acid every hour ; whilst the same extent 
of leaf, in the dark, emitted # 07 litre (4-27 cubic inches) of carbonic acid in the hour. 
Even under the influence of light, flowers have been found to absorb oxygen and evolve 
carbonic acid. 



70 



PREPARATION OF CARBONIC ACID. 



The production of carbonic acid in combustion, respiration, and fermentation, may 
be very easily proved by experiment. If a dry bottle be placed over a burning wax 
taper standing on the table, the sides of the bottle will 
be covered with dew from the combustion of the hydrogen 
in the wax ; and if a little clear lime-water be shaken in 
the bottle, the milky deposit of carbonate of lime wdll 
indicate the formation of carbonic acid. 

By arranging two bottles, as represented in fig. 64, and 
inspiring through the tube A, air will bubble through the 
lime-water in B, before entering the lungs, and will then 
be found to contain too little carbonic acid to produce a 
milkiness, but on expiring the air, it will bubble through 
C, and will render the. lime-water in this bottle very dis- 
tinctly turbid. 

If a little sugar be dissolved in eight or ten times its 
weight of warm (not hot) water, in the flask A (fig. 65), 
and a little dried yeast, previously rubbed down with water, 
added, fermentation will commence in the course of an hour 
or less, and carbonic acid may be collected in the jar B. 




Fie. 64. 



57. In the mineral kingdom free carbonic acid 
is pretty abundant. The gas issues from the earth 

in some places in considerable quantity, as at Nauheim, where there is 

said to be a spring exhaling about 1,000,000 lbs. of the gas annually. 

Many spring waters, those of Seltzer and Pyrmont, for example, are very 

highly charged with the gas. 

But it occurs in far larger quantity in a state of combination with lime, 

forming the immense deposits of limestone , marble, and chalk, which 

compose so large a portion 
of the crust of the globe. 
Carbonate of lime is also 
met with in the animal 
kingdom. Fish shells and 
pearls contain about two- 
thirds of their weight of 
this substance, whilst egg- 
shells contain as much as 
nine-tenths of carbonate of 
lime. 

The expulsion of the 
carbonic acid from lime- 
stone (CaO.C0 2 ) forms 
the object of the process 
of lime burning, by which' 
the large supply of lime 
(CaO) is obtained for build- 




Fig. 65. 



ing and other purposes. But if it be required to obtain the carbonic acid 
without regard to the lime, it is better to decompose the carbonate of lime 
with an acid. 

Preparation of carbonic acid. — The form of the carbonate of lime, and 
the nature of the acid employed, are by no means matters of indifference. 
If dilute sulphuric acid be poured upon fragments of marble, the effer- 
vescence which occurs at first soon ceases, for the surface of the marble 
becomes coated with the nearly insoluble sulphate of lime, by which it is 
protected from the further action of the acid — 

CaO. CO, + H. 2 O.SO, = CaO . S0 3 + Kfl + C0 2 . 

Marble. ' Sulphuric acid. Sulphate of lime. 



PROPERTIES OF CARBONIC ACID. 



71 



if the marble be finely powdered, or if powdered chalk be employed, each 
particle of the carbonate of lime will be acted upon. When lumps of 
carbonate of lime are acted upon by hydrochloric acid, there is no danger 
that any will escape the action of the acid, for the chloride of calcium 
produced is one of the most soluble salts — 



CaO.CO a + 2HC1 = CaCl 2 + 

Marble. Hydrochloric acid. ° c^icium^ 



H 2 



CO, 



For the ordinary purposes of experiment, carbonic acid is most easily 
obtained by the action of diluted hydrochloric acid upon small frag- 
ments of marble (fig. 66), the latter being 
covered with water, and hydrochloric acid 
poured in through the funnel-tube. The 
gas may be collected by downward dis- 
placement. 




Fig. 6Q. 



-Preparation of carbonic 
acid. 



58. Properties of carbonic acid. — Car- 
bonic acid gas is invisible, like the gases 
already examined, but is distinguished by 
a peculiar pungent odour, as is perceived 
in soda-water. It is more than half as 
heavy again as atmospheric air, its specific 
gravity being 1*529, which causes its ac- 
cumulation near the floor of such confined spaces as the Grotto del Cane, 
where it issues from fissures in the rock. 

The high specific gravity of carbonic acid may be shown by pouring it into a light 
jar attached to a balance, and counterpoised by a weight in the opposite scale 
(fig. 67). 




Fig. 67. 

Another favourite illustration consists in floating a soap-bubble on the surface of a 
layer of the gas generated in the large jar (fig. 68), by pouring diluted sulphuric acid 
upon a few ounces of chalk made into a thin cream with water. 

If a small balloon, made of collodion, be placed in the jar A (fig. 69), it will ascend 



72 



EXTINCTION OF FLAME BY CARBONIC ACID. 



If smouldering brown paper be held at the mouth of a jar, like that in tig. 69, the 
smoke will float upon the surface of the carbonic acid, and will sink with it on re- 
moving the stopper. 






The power which carbonic acid possesses of extinguishing flame is 
very important, and has received practical application in the case of burn- 
ing mines which must otherwise have 
been flooded with water.* Many at- 
tempts have also been made from time 
to time to employ this gas for sub- 
duing ordinary conflagrations, but their 
success has hitherto been very partial. 
It will be remembered that pure nitro- 
gen is also capable of extinguishing 
the name of a taper, but a large pro- 
portion of this gas may be present in 
air without affecting the flame, whereas 
a taper is extinguished in air contain- 
ing one-eighth of its volume of carbonic 
acid, and is sensibly diminished in bril- 
liancy by a much smaller proportion 
of the gas. 

The power of extinguishing flame, con- 
joined with the high density of carbonic 
acid, admit of some very interesting illus- 
Fig. 70. trations. 

Carbonic acid may be poured from some 
distance upon a candle, and will extinguish it at once. 

A large torch of blazing tow may be plunged beneath the surface of the carbonic 
acid in the jar, fig. 68. 

Carbonic acid may be raised in a glass bucket (fig. 70) from a large jar, and 
poured into another jar the air in which has been previously tested with a taper. 

A wire stand with several tapers fixed at different levels may be placed in the 
jar A, fig. 71, and carbonic acid gradually admitted through a flexible tube connected 

* All gases which take no part in combustion may extinguish flame, even in the presence 
of air, by absorbing heat and reducing the temperature below the burning-point. 




EFFECT OF CARBONIC ACID ON ANIMALS. 



73 




Fig. 71. 

the stand A (fig. 72) 
attached to the stand 



with the neck of the jar, from the cistern B, a hole in the cover of which allows air 
to enter it as the gas flows out; the flame of each 
taper will gradually expire as the surface of the car- 
bonic acid rises in the jar. 

A jar of oxygen may be placed over a jar of car- 
bonic acid, as shown in fig. 53, and a taper let down 
through the oxygen, in which it will burn bril- 
liantly, into the carbonic acid, which extinguishes 
it, and if it be quickly raised again into the oxygen, 
it will rekindle with a slight detonation. This alter- 
nate extinction and rekindling may be repeated several 
times. 

On account of this extinguishing power of 
carbonic acid, a taper cannot continue to burn 
in a confined portion of air until it has ex- 
hausted the oxygen, but only until its com- 
bustion has produced a sufficient quantity of 
carbonic acid to extinguish the flame. 

To demonstrate this, advantage may be taken 
of the circumstance that phosphorus will continue 
to burn in spite of the presence of carbonic acid. Upon 
a small piece of phosphorus is placed, and a taper is 
by a wire. The cork B fits air-tight into the jar, and 
carries a piece of copper wire bent so that it may be heated 
by the flame of the taper. A little water is poured into 
the plate to prevent the entrance of any fresh air. If the 
taper be kindled, and the jar placed over it, the flame 
will soon die out; and on moving the jar so that the hot 
wire may touch the phosphorus, its combustion will show 
that a considerable amount of oxygen still remains. 

In the same manner, an animal can breathe a 
confined portion of air only until he has charged 
it with so much carbonic acid that the hurtful effect 
of this gas begins to be felt, a considerable quantity of oxygen still 
remaining. 

If the air contained in the jar A (fig. 73), standing over water, be breathed two 
or three times through the tube B, a painful sense of oppression will soon be felt in 
consequence of the accumulation of car- 
bonic acid. By immersing a deflagrating 
spoon C, containing a piece of burning phos- 
phorus, and having a lighted taper attached, 
it may be shown that although there is 
enough carbonic acid to extinguish the taper, 
the oxygen is not exhausted, for the phos- 
phorus continues to burn rapidly. 

Carbonic acid is not poisonous when 
taken into the stomach, but acts most 
injuriously when breathed, by offering 
an obstacle to that escape of carbonic 
acid, by diffusion, from the blood of 
the venous circulation in the lungs, 
and its consequent replacement by the 
oxygen necessary to arterial blood. 
Any hindrance to this interchange 
must impede respiration, and such 
hindrance would, of course, be afforded 
by carbonic acid present in the air 
inhaled, in proportion to its quantity. 





Fig. 73. 
The difference in constitution and 



74 



PRINCIPLES OF VENTILATION. 



temperament in individuals makes it impossible that any exact general 
rule should he laid down as to the precise quantity of carbonic acid 
which may be present in air without injury to respiration, but it may be 
safely asserted that it is not advisable to breathe for any length of time 
in air containing more than T o 1 oo* n (0*1 P er cen t-) of its volume of car- 
bonic acid. 

There appears to be no immediate danger, however, until the carbonic 
acid amounts to -g-^th (0*5 per cent.), when most persons are attacked by 
the languor and headache attending the action of this gas. A larger pro- 
portion of carbonic acid produces insensibility, and air containing y^-th of 
its volume of carbonic acid causes suffocation. The danger in entering old 
wells, cellars, and other confined places, is due to the accumulation of 
this gas, either exhaled from the earth or produced by decay of organic 
matter. The ordinary test applied to such confined air by introducing a 
candle is only to be depended upon if the candle burns as brightly in the 
confined space as in the external air; should the flame become at all dim, 
it would be unsafe to enter, for experience has shown that combustion 
may continue for some time in an atmosphere dangerously charged with 
carbonic acid. 

The accidents from choke damp and after damp in coal mines, and 
from the accumulation, in brewers' and distillers' vats, of the carbonic acid 
resulting from fermentation, are also examples of the fatal effect of this 
gas. 

The air issuing from the lungs of a man at each expiration contains 
from 3 '5 to 4 volumes of carbonic acid in 100 volumes of air, and could not, 
therefore, be breathed again without danger. The total amount of car- 
bonic acid evolved by the lungs and skin amounts to about 0*7 cubic foot 
per hour. In order that it may be breathed again without inconvenience, 
this should be distributed through at least 140 cubic feet of fresh air, or a 
space measuring 5 -2. feet each way. Hence the necessity for a constant 
supply of fresh air by ventilation, to dilute the carbonic acid to such an 
extent that it may cease to impede respiration. This becomes the more 
necessary where an additional quantity of carbonic acid is supplied by 
candles or gas-lights. Two ordinary gas-burners, each consuming three 
cubic feet of gas per hour, will produce as much carbonic acid as one man. 
Fortunately, a natural provision for ventilation exists in the circumstance 
that the processes of respiration and combustion, which contaminate the 
air, also raise its temperature, thus diminishing its specific gravity by 

expansion, and causing it to ascend 
and give place to fresh air. Hence 
the vitiated air always accumulates 
near the ceiling of an apartment, and 
it becomes necessary to afford it an 
outlet by opening the upper sash of 
the window, since the chimney ven- 
HP tilates immediately only the lower 
jfjlp part of the room. " 



These principles may be illustrated by 

some very simple experiments. 

Fig. 74. Two quart jars (fig. 74) are filled with 

carbonic acid, and after being tested with 

a taper, a 4 oz. flask is lowered into each, one flask containing cold and the other 

hot water. After a few minutes, the jar with the cold flask will still contain enough 




PRINCIPLES OF VENTILATION. 



75 



carbonic acid to extinguish the taper, whilst the air in the other jar will support com- 
bustion brilliantly. 

A tall stoppered glass jar (fig. 75) is placed over a stand, upon which three lighted 
tapers are fixed at different heights. The vitiated air, rising to the top of the 
jar, will extinguish the uppermost taper first, and the others in succession. By 
quickly removing the stopper and raising the jar a little before the lowest taper has 
expired, the jar will be ventilated and the taper revived. 

A similar jar (fig. 76), with a glass chimney fixed into the neck through a cork or 
piece of vulcanised tubing, is placed over a stand with two tapers, one of which is 
near the top of the jar, and the other beneath the aperture of the chimney; if a 
crevice for the entrance of air be left between the jar and the table, the lower 
taper will continue to burn indefinitely, whilst the upper one will soon be extin- 
guished by the carbonic acid accumulating around it. 

In ordinary apartments, the incidental crevices of the doors and windows 
are depended upon for the entrance of fresh air, whilst the contaminated 
air passes out by the chimney, hut in large buildings special provision 
must be made for the two air currents. In -mines this becomes the more 
necessary, since the air receives much additional contamination by the 





Fig. 75. 



Fig. 76. 



gases (marsh-gas and carbonic acid) evolved from the workings, and by 
the smoke occasioned in blasting with gunpowder. Mines are generally 
provided with two shafts for ventilation, under one of which (the upcast 
shaft) a fire is maintained to produce the upward current, which carries off 
the foul air, whilst the fresh air descends by. the other (downcast shaft). 
The current of fresh air is forced by wooden par- 
titions to divide itself, and pass through every 
portion of the workings. 

The operation of such provisions for ventilation is easily 
exhibited. 

A tall jar (fig. 77) is fitted with a ring of cork, carrying 
a wide glass chimney (A). If this be placed over a taper 
standing in a plate of water, the accumulation of vitiated 
air will soon extinguish the taper; but if a second chimney 
(B), supported in a wire ring, be placed within the wide 
chimney, fresh air will enter through the interval be- 
tween the two, and the smoke from a piece of brown 
paper will demonstrate the existence of the two currents, 
as shown by the arrows. 

A small box (fig. 78) is provided with a glass chimney 
at each end. In one of these (B) representing the upcast 
shaft, a lighted taper is suspended. A piece of smoking 
brown paper may be held in each chimney to show the 
direction of the current. On closing A with a glass 
plate, the taper in B will be extinguished, the entrance 
of fresh air being prevented. By breathing gently into A the taper will also be 




76 



SODA WATER — SPARKLING DRINKS. 




Fig. 78. 



extinguished. The experiment may be varied by pouring carbonic acid and oxy- 
gen alternately into A, when the taper will be extinguished and rekindled by turns. 

A pint bell-jar (fig. 79) is placed over a taper standing in a tray of water. If a 
chimney (a common lamp-glass) be placed on the top of the jar, the flame of the 
taper will gradually die out, because no provision exists for the establishment of 
the two currents, but on dropping a piece of tin-plate or card- board into the chimney, 
so as to divide it, the taper will be revived, and the smoke from the brown paper will 
distinguish the upcast from the downcast shaft. 

If a little water be poured into a wide-mouthed bottle of carbonic 
acid, and the bottle be then firmly closed by the palm of the hand, it 

will be found, on shaking the bottle 
violently, that the carbonic acid is 
absorbed, and the palm of the hand 
is sucked into the bottle. The pre- 
sence of carbonic acid in the solution 
may be proved by pouring it into 
lime-water, in which it will produce a 
precipitate of carbonate of lime, re- 
dissolved by a further addition of the 
solution of carbonic acid. 

One pint of water shaken in a vessel 
containing carbonic acid gas, at the 
ordinary pressure of the atmosphere, will dissolve about one pint of the 
gas, equal in weight to nearly 1 6 grains. If the carbonic acid be confined 
in the vessel under a pressure equal to twice or thrice that of the atmo- 
sphere — that is, if twice or thrice the quantity of carbonic acid be com- 
pressed into the same space, the water will still dissolve one pint of the 
gas, but the weight of this pint will now be twice 
or thrice that of the pint of uncompressed gas, so 
that the water will have dissolved 32 or 48 grains of 
the gas, accordingly as the pressure had been doubled 
or trebled. As soon, however, as the pressure is 
removed, the compressed carbonic acid will resume 
its former state, with the exception of that portion 
which the water is capable of retaining in solution 
under the ordinary pressure of the atmosphere. 
Thus, if the water had been charged with carbonic 
acid under a pressure equal to thrice that of the 
atmosphere, and had therefore absorbed 48 grains 
of the gas, it would only retain 16 grains when the 
pressure was taken off, allowing 32 grains to escape 
in. minute bubbles, producing the appearance known 
as effervescence. This affords an explanation of the 
properties of soda-water, which is prepared by charging water with 
carbonic acid gas under considerable pressure, and rapidly confining it 
in strong bottles. As soon as the resistance offered by the cork to the 
expansion of the gas is removed, the excess of the carbonic acid, above 
that which it can hold in solution at the ordinary pressure of the air, 
escapes with effervescence. In a similar manner, the waters of certain 
springs become charged with carbonic acid, under high pressure, beneath 
the surface of the earth, and when, upon their rising to the surface, this 
pressure is removed, the excess of carbonic acid escapes with effervescence, 
giving rise to the sparkling appearance and sharp flavour which renders 
spring water so agreeable. On the other hand, the waters of Jakes and 




LIQUEFACTION OF CARBONIC ACID. 77 

rivers are usually flat and insipid, because they hold in solution so small 
a quantity of uncombined carbonic acid. 

The sparkling character of champagne, bottled beer, &c, is due to the 
presence in these liquids of a quantity of carbonic acid which has been 
generated by fermentation, subsequent to bottling, and has therefore been 
retained in the liquid under pressure. In the case of Seidlitz powders 
and soda-water powders, the effervescence caused by dissolving them 
in water is due to the disengagement of carbonic acid, caused by 
the action of the tartaric acid, which composes one of the powders, 
upon the bicarbonate of soda, producing tartrate of soda and carbonic 
acid gas. In the dry state these powders may be mixed without any 
chemical change, but the addition of water immediately causes the effer- 
vescence. 

The solubility of carbonic acid in water is of great importance in the 
chemistry of Nature ; for this acid, brought- down from the atmosphere 
dissolved in rain, is able to act chemically upon rocks, such as granite, 
which contain alkalies — the carbonic acid combining with these, and thus 
slowly disintegrating or crumbling down the rock, an effect much assisted 
by the mechanical action of the expansion of freezing water in the inter- 
stices of the rock. It appears that soils are thus formed by the slow 
degradation of rocks, and when these soils are capable of supporting- 
plants, the solution of carbonic acid is again of service, not only as a 
direct food, by providing the plant with carbon through its roots, but as 
a solvent for certain portions of the mineral food of the plant (such as 
phosphate of lime), which pure water could not dissolve, and which the 
plant cannot take up except in the dissolved state. 

59. Although carbonic acid retains its state of gas under all tempera- 
tures and pressures to which it is commonly exposed, it is capable of 
assuming the liquid and 3ven the solid state. 

At about the ordinary temperature (59° F.) carbonic acid is condensed, 
by a pressure of 50 atmospheres (750 lbs. per square inch), to a colourless 
liquid of sp. gr. 0*83 (water = 1), and at a temperature of — 70° F. (70° 
below the zero, or 102° below the freezing point, F.) becomes a transparent 
mass of solid carbonic acid resembling ice. 

If the temperature of the gas be reduced to~32° F. a pressure of 38'5 
atmospheres only will suffice to liquefy it. 

The experiments of Andrews upon the liquefaction of carbonic acid show that, in 
causing the liquefaction of gases, increase of pressure is not always equivalent to 
reduction of temperature, but that there exists a particular temperature for each gas 
above which no amount of pressure is able to liquefy it, and at this particular tempera- 
ture, the critical point, the gas is wavering between the gaseous and the liquid state, 
so that "the gaseous and liquid states are only widely separated forms of the same 
condition of matter, and may be made to pass into one another by a series of grada- 
tions so gentle, that the passage shall nowhere present any interruption or breach of 
continuity." It was found to be impossible to liquefy carbonic acid above a tem- 
perature of 88° F., even by a pressure of 109 atmospheres ; but, at this high pressure, 
the gas ceased to obey the law that the volume of a gas is inversely as the pressure, 
for instead of occupying T -J-g- of its original volume, it had been reduced to T ^- s . On 
cooling the gas thus compressed, it liquefied suddenly, and not gradually as in the 
case of a vapour under ordinary pressure. The gas in this condition, when subjected 
to very small variations of temperature or pressure, exhibits curious nickering move- 
ments, resembling the effect produced by the ascent of columns of heated air through 
colder strata. 

Even at 55° F., a pressure of 48*89 atmospheres reduced the gas (not to -fa but) to 
-jV of its original volume without liquefying it, but at this point, an additional pres- 
sure of only -fa atmosphere suddenly liquefied one half of the gas. 



78 



LIQUEFACTION OF CARBONIC ACID. 




Fiff. 80. 



A small specimen of liquid carbonic acid is easily prepared. A strong tube of 
green glass (A, fig. 80 is selected, about 12 inches long, fa inch, diameter in the 

bore, and fa inch thick in the 

A walls. With the aid of the 

f' ! . v blowpipe flame this tube is 

softened and drawn off at 

^jb ^ about an inch from one end, 

lU^^ 5 ^ — — ■, — =J as at B, which is thus closed 

(C). This operation should 
be performed slowly, in order 
that the closed end may not 
be much thinner than the 
walls of the tube. When the 
tube has cooled, between 30 
and 40 grs. of powdered bi- 
carbonate of ammonia (ordi- 
nary sesquicarbonate which 
has crumbled down) are 
tightly rammed into it with 
a glass rod. This part of the 
tube is then surrounded with 
a few folds of wet blotting- 
paper to keep it cool, and the 
tube is bent, just beyond the 
carbonate of ammonia, to a 
somewhat obtuse angle (D). 
The tube is then softened at 
about an inch from the open 
end, and drawn out to a narrow neck (E), through which a measured drachm of oil 
of vitriol is poured down a funnel-tube, so as not to soil the neck, which is then 
carefully drawn out and sealed by the blowpipe flame, as at F. The empty space 
in the tube should not exceed ^ cubic inch. 

When the tube is thoroughly cold, it is suspended by strings in such a position 
that the operator, having retired behind a screen at some distance, may reverse the 
tube, allowing the acid to flow into the limb containing the carbonate of ammonia ; 
or the tube may be fixed in a box which is shut up, and reversed so as to bring the 
tube into the required position. 

If the tube be strong enough to resist the pressure, it will be found, after a few 
hours, that a layer of liquid carbonic acid has been formed upon the surface of the 
solution of sulphate of ammonia. By cooling the empty limb in a mixture of 
pounded ice and salt, or of hydrochloric acid and sulphate of soda, the liquid acid 
can be made to distil itself over into this limb, leaving the sulphate of ammonia in 
the other. 

Fig. 81 represents Thilorier's apparatus for the preparation of several pints of 
liquid carbonic acid, g is a strong wrought iron generator of gas in which 2 lbs. of 
bicarbonate of soda are well stirred with 4 pints of water at 100° F. Half a pint of 
oil of vitriol is poured into a brass tube which is dropped upright into the generator, 
as shown by the dotted lines in the figure, which also indicate the level of the liquid 
in the generator. The head of the generator is then firmly screwed on, with the help 
of the spanners represented in the figure, and the stopcock* firmly closed by turning 
the wheel w. The generator is then turned over and over on its trunnions resting 
upon the stand s, for ten minutes, so that the whole of the sulphuric acid may be 
mixed with the solution of bicarbonate of soda. The generator is then connected, by 
the copper tube t with the strong wrought iron receiver r, the stopcock of which is 
attached to a tube passing down to the bottom of the vessel. The stopcock of the 
receiver is then opened, by turning the wheel v, and afterwards that of the generator. 
The condensed gas then passes over into the receiver. After- two or three minutes 
the stopcocks are again closed, the generator detached, the waste gas blown out 
through the stopcock, the head unscrewed, and the generator emptied and recharged. 
After the operation has been repeated three times, the pressure in the receiver will 
be found to have liquefied some of the carbonic acid, and after seven charges, the 
receiver is nearly filled with the liquid acid. The tube t is then unscrewed from the 

* These stopcocks are steel screws with conical points fitting into gun-metal sockets. 
Leaden washers are employed to secure the tightness of the joints' between the iron vessels 
and their heads, which are made of gun-metal. 



LIQUEFACTION OF CARBONIC ACID. 79 

receiver, and replaced by the nozzle n. If the stopcock be then slightly opened, a 
stream of the liquid will be forced up the tube, and, issuing into the air, will congeal 
by its own evaporation into an opaque white spray of solid carbonic acid. 




Fig. 81. — Liquefaction of carbonic acid. 

In order to collect the solid, the box shown at b is employed. This is made of 
brass, and furnished with strong flanges by which the cover is secured to it. The 
handles of the box are made of wood or gutta percha, and are hollow, with brass 
tubes passing through them to allow of the escape of the gaseous carbonic acid, the 
ends of the tubes within the box being covered by perforated plates which prevent 
the escape of the solid acid. The box and its cover having been fitted together, the 
nozzle of the receiver r is inserted into a short tube projecting from the side of the 
box, and whilst one operator holds the box firmly by the handles, 
another gradually opens the stopcock by turning the wheel v. 
A stream of the liquid acid is at once forced into the box, 
where it strikes against a curved brass plate arranged so as to 
force it to pass all round the inside of the box ; about seven- 
eighths of it evaporate as gas, which rushes out through the 
tubular handles, and the rest is found in the box in a solid state, 
resembling snow. It should be quickly shaken on to a sheet of 
paper, and emptied into a beaker placed within a larger beaker, 
the interval being filled up by flannel. By covering the beaker 
with a dial glass, the solid acid may be kept for some time. 
The box becomes intensely cold, and condenses the moisture of 
the air to a thick layer of hoar frost, and if it be dipped into 
water it becomes coated with ice. 

The solid carbonic acid evaporates without melting, for its 
melting-point is -85°F., and its own evaporation keeps it at 
-125° F. It produces a sharp sensation of cold when placed 
upon the hand, and if pressed into actual contact with the 
skin, causes a painful frost-bite. Its rapid evaporation may 
be shown by placing a few fragments on the surface of water 
in the globe (fig. 82), which has a tube passing down to the 
bottom, through which the pressure of the carbonic gas forces 
the water to a considerable height. 

The solid carbonic acid is soluble in ether, and it evaporates 
from this solution far more rapidly, because the liquid is a better conductor of heat 
than the highly porous solid, and abstracts heat more rapidly from surrounding 
objects. 

If a layer of ether be poured upon water, and some solid carbonic acid be thrown 
into it, the water is covered with a layer of ice. 




Fi£. 82. 



80 



ANALYSIS OF ORGANIC SUBSTANCES. 



On immersing the bulb of a thermometer into the solution of solid carbonic acid 
in ether, the mercury becomes solid, and the bulb may be hammered out into a disk. 

By placing a piece of filter-paper in an evaporating dish, pouring a pound or 
so of mercury into it, immersing a wire turned into a fiat spiral at the end, covering 
the mercury with ether,* and throwing in some solid carbonic acid, the mercury 
may soon be frozen into a cake. If this be suspended by the wire in a vessel of 
water, the mercury melts, descending in silvery streams to the bottom of the 
vessel, leaving a cake of ice on the wire, with icicles formed during the descent of 
the mercury. 

Even in a red hot vessel, with prompt manipulation, the mercury may be solidified 
by the solution of solid carbonic acid in ether. 

The temperature produced by the evaporation of the solid carbonic dissolved in 
ether is estimated at — 150°F. 

60. Carbonic acid may be separated from most other gases by the 
action of hydrate of potash, which absorbs it, forming carbonate of potash. 
The proportion of carbonic acid is inferred either from the diminution in 
volume suffered by the gas when treated with potash, or from the increase 
of weight of the latter. 

In the former case the gas is carefully measured over mercury (fig. 83), with due 
attention to temperature and barometric pressure, and a little concentrated solution 

of potash is thrown up through a curved 
pipette or syringe, introduced into the 
orifice of the tube beneath the surface of 
the mercury. The tube is gently shaken 
for a few seconds to promote the absorp- 
tion of the gas, and, after a few minutes' 
rest, the diminution of volume is read 
off. Instead of solution of potash, damp 
hydrate of potash in the solid state is 
sometimes introduced, in the form of 
small sticks or balls attached to a wire. 
To determine the weight of carbonic 
acid in a gaseous mixture, the latter is 
passed through a bulb-apparatus (C, fig. 
84), containing a strong solution of po- 
tash, and weighed before and after the 
passage of the gas. When the propor- 
tion of carbonic acid in the gas is small, 
it is usual to attach to the bulb-appara- 
tus a little tube, containing solid hydrate 
of potash, or chloride of calcium, or 
pumice stone moistened with sulphuric 
acid, for the purpose of retaining any 
vapour of water which the large volume of unabsorbed gas might carry away in 
passing through the solution of potash. 

61. Ultimate organic analysis. — It is necessary to determine in this 
manner the weight of carbonic acid, in order to ascertain the proportion 
of carbon present in organic substances. For this purpose, an accurately 
weighed quantity (usually from seven to ten grains) of the organic sub- 
stance is very carefully mixed with some compound from which it can 
obtain oxygen at a high temperature, such as oxide of copper (CuO) or 
chromate of lead (PbO.Cr0 3 ), care being taken to employ a large excess 
of the oxidising agent. The mixture is introduced into a combustion-tube 
of German glass (which is free from lead and noted for its infusibility) of 
the form shown in A, fig. 84. This tube is provided with a small tube B, 
containing chloride of calcium, which is connected by a tube of caoutchouc 
with the potash-bulbs C. On gradually heating the tube in a charcoal 




* Much economy of 
these experiments. 



Lid carbonic acid results from the use of the anaesthetic ether in 



ANALYSIS OF ORGANIC SUBSTANCES. 



81 



furnace, or over a properly constructed gas-burner, the hydrogen and carbon 
contained in the organic substance are converted, respectively, into water 
and carbonic acid, by the oxygen derived from the chromate of lead or 
oxide of copper. The water is absorbed by the chloride of calcium in B 
and the increase of weight in this tube will indicate the quantity of water 
formed in the combustion, whilst that of the potash bulbs will show the 
weight of the carbonic acid. When the whole length of the tube is red 
hot, and no more gas passes through the bulbs, the sealed point D of the 
tube is broken off, and air drawn through by applying suction at E, in 




Fig. 84. — Apparatus for organic analysis. 



order to sweep out the last traces of water and carbonic acid into the 
chloride of calcium and potash. Sometimes the organic substance is 
heated in a little platinum tray, placed within a glass tube, through which 
a stream of pure oxygen is passed, the products of combustion being 
afterwards made to pass over red hot oxide of copper, to convert any 
carbonic oxide into carbonic acid, and collected for weighing as before. 

When the organic substance contains carbon, Irydrogen, and oxygen, 
the weight of this last is inferred by subtracting the weights of the carbon 
and hydrogen from that of the substance. As an example of the ultimate 
analysis of an organic substance, the results of an analysis of oxalic acid 
are here given — 

10 grs. of oxalic acid, dried at 212° F., gave 9*78 grs. of carbonic acid 
and 2 '00 grs. of water. 



CO. 



CO. 



c 

44 : 12 : : 9'78 : x 
x— 2 "67 grs. of carbon in 10 grs. of oxalic acid. 



H 2 

18 



H, 



H 2 

2-00 



y 



y-0'22 gr. of hydrogen in 10 grs. of oxalic acid. 

It having been ascertained by preliminary experiments that oxalic acid 
contains only carbon, hydrogen, and oxygen, 10 (oxalic acid) minus 2 "89 
(carbon and hydrogen) = 7 "11 grs. of oxygen in 10 grs. of oxalic acid. 

It appears, therefore, that 

10 grs. of oxalic acid contain 
2-67 „ carbon, 
0-22 „ hydrogen, and 
7*11 „ oxygen. 



82 EMPIRICAL AND RATIONAL FORMULAE. 

Empirical and rational formula*. — In order to deduce from these 
numbers the chemical formula for oxalic acid, that is, the formula ex- 
pressing the number of atoms of each element, it will be necessary, of 
course, to divide the weight of each element by the number representing 
its atomic weight. 

Thus 2*67 -r- 12 = 0*22 atomic proportion of carbon; 

0-22 - 1 = 0-22 „ „ hydrogen; 

7-11 ■*■ 16 = 0-44 „ „ oxygen. 

And the formula of oxalic acid might be written C. 22 H. 22 0. 44 . But as 
fractions are not admissible in such a formula, it would be written 
C 22 H 22 44 . This, however, is only an empirical formula for oxalic acid, 
that is, a formula which represents its composition only, without reference 
to its constitution, i.e., to the absolute number of atoms present, and to 
the mode in which they are grouped or arranged within the compound. 
A formula professing to give such information would be termed a rational 
formula, and can only be arrived at by the careful study of the relation 
of the substance under examination to others of which the combining 
weights are certainly known. Thus, it is found that one molecule (56 
parts) of caustic potash (KHO) requires 45 parts of dry oxalic acid to 
neutralise it and form the oxalate of potash. Hence it is reasonable to 
regard 45 as the molecular weight of dry oxalic acid. Since the above 
analysis has proved this quantity of oxalic acid to contain 12 (one atom) of 
carbon, 1 (one atom) of hydrogen, and 32 (two atoms) of oxygen, the formula 
would be written CH0 2 . The action of oxalic acid upon caustic potash 
would then be represented by the equation KHO + CH0 2 = H 2 + CK0 2 
(oxalate of potash). But there is another oxalate which has the formula 
C 2 KH0 4 (binoxalate of potash) in which only one half of the hydrogen 
is displaced by potassium. Hence there must be two atoms of hydrogen 
in the molecule of oxalic acid, and its formula is C 2 H 2 4 . In determining 
whether this formula represents only one grouping of the elements, or 
whether it contains two or more groups in combination, the chemist is 
guided by the results of a more minute study of the decompositions which 
the compound undergoes under varied conditions. 

62. Salts formed by carbonic acid. — Although so ready to combine with 
the alkalies and alkaline earths (as shown in its absorption by solution 
of potash and by lime-water), carbonic acid must be classed among the 
weaker acids. It does not neutralise the alkalies completely, and it may 
be displaced from its combinations with bases by most other acids. Its 
action upon the colouring matter of litmus is feeble and transient. If a 
solution of carbonic acid in water be added to blue infusion of litmus, a 
wine-red liquid is produced, which becomes blue again when boiled, losing 
its carbonic acid; whilst litmus reddened by sulphuric, hydrochloric, 
or nitric acid, acquires a brighter red colour, which is permanent on 
boiling. 

With each of the alkalies carbonic acid forms two well-defined salts, 
the carbonate and bicarbonate. Thus, the carbonates of potash and soda 
are represented by the formulae, K 2 O.C0 2 and ]STa 2 O.C0 2 , whilst the 
bicarbonates are KHO.C0 2 and NaHO.C0 2 . The existence of the latter 
salts would favour the belief in the existence of a hydrate of carbonic acid 
(H 2 O.C0 2 ), although no such combination of water with carbonic acid 
has yet been obtained in the separate state. Perfectly dry carbonic acid 



CARBONATES. 



83 



gas is not absorbed by pure quicklime (CaO), but when a little water is 
added, combination at once takes place. This supports the view enter- 
tained, by some chemists, that C0 2 is not an acid until it is associated 
with water, and they therefore speak of it as carbonic anhydride, reserving 
the name carbonic acid for the as yet undiscovered compound H 2 O.C0 2 
(or H 2 C0 3 ). 

Opposed to this view, however, is the fact that quicklime will absorb 
carbonic acid when heated to a certain point. 

Two hard glass tubes closed at one end, and bent as 
in fig. 85, are perfectly dried, and filled, over mer- 
cury, with well-dried carbonic acid gas. Fragments of 
lime are taken, whilst red hot, out of a crucible, cooled 
under the mercury, inserted into the tubes, and trans- 
ferred to the upper end. No absorption of the carbonic 
acid takes place, though, the tubes be left for some 
days ; but if one of them be heated by a Bunsen 
burner, the absorption of carbonic acid takes place 
rapidly, and the mercury is forced up into the tube. 

The carbonates may be expressed either by additive 
formulae, showing the bases which combine with car- 
bonic acid to produce them, or by substitutive formulae, 
in which they are represented as formed from the hypo- 
thetical H 2 C0 3 by the substitution of metals for the 
hydrogen. In the latter formulae the existence of C0. 2 !|§§SliJ 
is lost sight of altogether. 

The following are some of the principal 
carbonates which are found in nature or employed in the 




Chemical Name. Common Name. 


Additive Formula. 


Substitutive Formula. 


Carbonate of pot- 
ash 


I Potashes, Pearl-ash 


K 2 . C0 2 


K 2 C0 3 


Bicarbonate of 

potash 
Carbonate of 

soda 
Bicarbonate of 

soda 


| 


K 2 . H 2 . 2C0 2 


KHC0 3 


j Alkali ) 
I Washing soda f 

[ Carbonate of soda 


Na 2 . CO*. 
Na 2 H 2 . 2C0 2 


Na 2 C0 3 
NaHC0 3 


Sesquicarbonate 
of ammonia 


( Smelling salts j 
) Preston salts f 
j Carbonate of am- ( 


4KH 3 .2H 2 0.3C0 2 


2[(H 4 N) 2 C0 3 ]C0 2 


Carbonate of 

lime 
Basic carbonate 

of magnesia 
Carbonate of 

iron 


( monia ) 
{ Limestone, ehalk ) 
I Marble \ 
\ Magnesia alba ) 
{ Magnesia ) 

I Spathic iron ore 


CaO . C0 2 

3(MgO.C0 2 ), | 
MgO . H 2 0. j 

FeO . C0 2 


CaC0 3 

3MgCO s • MgH 2 2 

FeC0 3 


Carbonate of 
zinc 


I Calamine 


ZnO . C0 2 


ZnC0 3 


Basic carbonate 
of copper 

Basic carbonate 
of lead 

Double carbon- 
ate of lime 
and magnesia 


J Malachite j 

j White lead j 

( Dolomite j 
< Magnesian lime- > 
( stone ) 


CuO . C0 2 , ) 
CuO . H 2 j 
2(PbO . C0. 2 ), ) 
PbO . H 2 j 

CaO . MgO . 2C0 2 


CuO . H 2 . C11CO3 
2PbC0 3 . PbO . H 2 

MgCa2C0 3 



8J: 



CARBONIC OXIDE. 



63. Analytical proof of the composition of carbonic acid. — Lavoisier appears to have 
been the first to prove that carbonic acid was formed when carbon combined with 
oxygen, but its composition was first analytically demonstrated by Smithson Ten- 
nant, who heated carbonate of lime with phosphorus in a sealed glass tube, and 
obtained phosphate of lime and carbon, the latter having parted with its oxygen to 
convert the phosphorus into phosphoric acid. 

A far easier method of demonstrating the composition of carbonic acid consists in 
introducing a pellet of potassium into a bulb tube, through which a current of car- 
bonic acid (dried by passing through oil of vitriol, or over chloride of calcium) is 
flowing, and applying the heat of a spirit-lamp to the bulb. The metal will soon 
burn in the gas, which it robs of its oxygen, leaving the carbon as a black mass upon 
the bulb (fig. 86). The potash produced by the oxidation of the potassium enters 
into combination with another portion of the carbonic acid, forming a white mass of 
carbonate of potash, 3C0 2 + K 4 = 2(K 2 . C0 2 ) + C. If slices of sodium be arranged 
in a test-tube in alternate layers with dried chalk (carbonate of lime), and strongly 
heated with a spirit-lamp, vivid combustion will ensue, and much carbon will be 
separated (CaO . C0 2 + Na 4 = CaO + 2Na 2 + C). 

When the action of the sodium upon carbonic acid is moderated by employing it 
in the form of a mixture with pure dry sand, and by keeping the temperature below 
the boiling-point of mercury, oxalate of sodium is produced by the combination of the 
sodium with the elements of the carbonic aeid, Na 2 + 2C0 2 = Na. 2 C 2 4 (oxalate of 
sodium). 




Fig. 



64. Carbonic oxide (CO = 28 parts by weight = 2 volumes). — Other 
metals, which are not endowed with so powerful an attraction for oxygen, 
do not carry the decomposition of carbonic acid to its final limit ; thus, 
iron and zinc* at a high temperature will only deprive the gas of one-half 
of its oxygen, a result which may also be brought about at a red heat by 
carbon itself. If an iron tube filled with fragments of charcoal be heated 
to redness in a furnace (fig. 9), and carbonic acid gas be transmitted 
through it, it will be found, on collecting the gas which issues from the 
other extremity of the tube, that it has no longer the properties of carbonic 
acid, but that, on the approach of a taper, it takes fire, and burns with a 
beautiful blue lambent flame, similar to that which is often observed to 
play over the surface of a clear fire. Both flames, in fact, are due to the 
same gas, and in both cases this gas results from the same chemical 
change, for in the tube the carbonic acid yields half of its oxygen to the 
charcoal, both becoming converted into carbonic oxide • C0 2 + C = 2 CO. 
In the fire, the carbonic acid is formed by the combustion of the carbon 
of the fuel in the oxygen of the air entering at the bottom of the grate ; 
and this carbonic acid, in passing over the layer of heated carbon in the 
upper part of the fire, is partly converted into carbonic oxide, which 

* Magnesium also reduces carbonic acid to carbonic oxide. 



CAKBONIC OXIDE IN FIRES AND FURNACES. 



85 



inflames when it meets with the oxygen in the air above the surface of the 
fuel, and burns with its characteristic blue flame, reproducing carbonic 
acid. 

The carbonic oxide occupies twice the volume of the carbonic acid from 
which it was produced. 

This conversion of carbonic acid into carbonic oxide is of great import- 
ance on account of its extensive application in metallurgic operations. It 
is often desirable, for instance, that a flame should be made to play over 
the surface of an ore placed on the bed or hearth of a reverberatory fur- 
nace (fig. 87). This object is easily attained when the coal affords a lame 




Reverberatory furnace for copper smelting. 



quantity of inflammable gas ; but with anthracite coal, which burns with 
very little flame, and is frequently employed in such furnaces, it is neces- 
sary to pile a high column of coal upon the grate, so that the carbonic 
acid formed beneath may be converted into carbonic oxide in passing over 
the heated coal above, and when this gas reaches the hearth of the fur- 
nace, into which air is admitted, it burns with a flame which spreads 
over the surface of the ore. 

The attraction of carbonic oxide for oxygen is turned to account in 
removing that element from combination with iron in its ores, as will be 
seen hereafter. 

Carbonic oxide is a gas of so poisonous a jcharacter that, according to 
Leblanc, one volume of it diffused through 100 volumes of air totally 
unfits it to sustain life; and it appears that the lamentable accidents 
which too frequently occur from burning charcoal or coke in braziers and 
chafing-dishes in close rooms, result from the poisonous effects of the small 
quantity of carbonic oxide which is produced and escapes combustion, 
since the amount of carbonic acid thus diffused through the air is not 
sufficient in many cases to account for the fatal result. 

65. The knowledge of this poisonous character of carbonic oxide gave 
rise, a few years since, to considerable apprehension when it was proposed 
to employ this gas in Paris for purposes of illumination. The character 
of the flame of carbonic oxide would appear to afford little promise of its 
utility as an illuminating agent ; but that it is possible so to employ it is 
easily demonstrated, by kindling a jet of the gas which has been passed 
through a wide tube containing a little cotton moistened with rectified 
coal naphtha (benzole), when it will be found to burn with a very luminous 
flame. The carbonic oxide destined to be employed for illuminating pur- 
poses was prepared by passing steam over red hot coke or charcoal, when 



86 



PREPARATION OF CARBONIC OXIDE. 



a highly inflammable gas was obtained, containing carbonic acid, carbonic 
oxide and hydrogen — 



4H 2 



+ a 



CO., + 2CO + H 



Since neither hydrogen nor carbonic oxide burns with a luminous flame, 
this gas was next passed into a vessel containing red-hot coke, over which 
melted resin was allowed to trickle. The action of heat upon the resin 
gave rise to the production of vapours similar to that of the benzole em- 
ployed in the above experiment, and which, in like manner, conferred 
considerable illuminating power upon the gas. 

The decomposition of steam by red-hot carbon is also taken advantage 
of in order to procure a flame from anthracite coal when employed for 
heating boilers. The coal being burnt on fish-bellied bars, beneath which 
a quantity of water is placed, the radiated heat converts the water into 
steam, which is carried by the draught into the fire, where it furnishes car- 
bonic oxide and hydrogen, both capable of burning with flame under the 
bottom of the boiler. The temperature of the bars is also thus reduced, so 
that they are not so much injured by the intense heat of the glowing fuel. 

66. Carbonic oxide, unlike carbonic acid, is a permanent gas, and 
nearly insoluble in water. It is even lighter than air, its specific gravity 
being 0*9 6 7. In its chemical relations it is an indifferent oxide, that is, 
it has neither acid nor basic properties. 

67. A very instructive process for obtaining carbonic oxide, consists in heating 
crystallised oxalic acid with three times its weight of oil of vitriol. If the gas be 
collected over water (fig. 88), and one of the jars be shaken with a little lime-water, 

the milkiness imparted to the 
latter will indicate abundance of 
carbonic acid ; whilst, on remov- 
ing the glass plate, and applying 
a light, the carbonic oxide will 
burn with its characteristic blue 
flame. The gas thus obtained is 
a mixture of equal volumes of 
carbonic oxide and carbonic acid 
gases. Crystallised oxalic acid 
is represented by the formula 
C ? H 2 4 . 2Aq., and if the water 
of crystallisation be left out of 
consideration, its decomposition 
may be represented by the equa- 
tion — 



C 2 H 2 4 = H 2 + CO + C0 2 , 

the change being determined by 
the attraction of the oil of vitriol for water. To obtain pure carbonic oxide, the 
mixture of gases must be passed through a bottle containing solution of potash, to 
absorb the carbonic acid (fig. 89). 

But pure carbonic oxide is much more easily obtained by the action of four parts 
of oil of vitriol upon one part of crystallised ferrocyanide of potassium (yellow prus- 
siate of potash) at a moderate heat, the lamp being removed as soon as the effer- 
vescence begins to take place. Since the gas contains, especially at the commence- 
ment, small incidental quantities of sulphurous and carbonic acids, it must be passed 
through solution of potash if it be required perfectly pure. The chemical change 
which occurs in this process is expressed thus : — 

K 4 C 6 N § Fe + 6H 2 + 6(H 2 . S0 3 ) = 
Ferrocyanide of 
potassium. 

GCO + 2(K 2 O.S0 3 ) + 3[(NH S V, . H 2 . S0 3 ] + FeO . S0 3 

Sulphate of potash. Sulphate of ammonia. Sulphate of iiou. . 




CARBONIC OXIDE. 



8" 



68. To demonstrate the production of carbonic acid during the combustion of 
carbonic oxide, a jar of the gas is closed with a glass plate, and after placing it upon 
the table, the plate is slipped aside and a little lime-water quickly poured into the 
jar. On shaking, no milkiness indicative of carbonic acid should be perceived. The 
plate is then removed, and the gas kindled. On replacing the plate and shaking the 
jar, an abundant precipitation of carbonate of lime will take place. 




Fig. 89. — Preparation of carbonic oxide. 

When carbonic oxide is passed through a red hot porcelain tube, a portion of it is 
decomposed into carbonic acid and carbon ; and when the experiment is conducted 
without special arrangements, the carbonic oxide is reproduced as the temperature of 
the gas falls. But by passLig through the centre of the porcelain tube a brass tube, 
through which cold water is kept running, the decomposition has been demonstrated 
by the deposition of carbon upon the cooled tube, and by collecting the carbonic acid 
formed. 

Carbonic acid is also decomposed by intense heat into carbonic oxide and oxygen ; 
but if these gases be allowed to cool down slowly in contact, they recombine. The 
gas drawn from the hottest region of a blast-furnace (see Iron), and rapidly 
"cooled, so as to prevent recombination, was found to -contain both carbonic oxide and 
oxygen. 

By passing a pellet of phosphorus up into carbonic acid, over mercury, in a eudio- 
meter and passing electric sparks for some days, the gas has been entirely decom- 
posed, an equal volume of carbonic oxide being left. 




Fig. 90. — Reduction of oxide of copper by carbonic oxide. 



The reducing action of carbonic oxide upon metallic oxides, at high temperatures, 
may be illustrated by passing the pure, gas from a bag or gas-holder, first through 



88 COMPOUNDS OF CARBON AND HYDROGEN. 

a bottle of lime-water (B, tig. 90), to prove the absence of carbonic acid, then over 
oxide of copper, contained in the tube C, and afterwards again through lime-water 
in D. When enough gas has been passed to expel the air, heat may be applied to 
the tube by the gauze-burner E, when the formation of carbonic acid will be im- 
mediately shown by the second portion of lime-water, and the black oxide of copper 
will be reduced to red metallic copper. 

If precipitated peroxide of iron be substituted for oxide of copper, iron in the state 
of black powder will be left, and if allowed to cool in the stream of gas, will take fire 
when it is shaken out into the air, becoming reconverted into the peroxide (iron 
pyrqphorus). 

69. Composition by volume of carbonic oxide and carbonic acid.- -When 
carbon burns in oxygen, the volume of the carbonic acid produced is 
exactly equal to that of the oxygen, so that one volume of oxygen fur- 
nishes one volume of carbonic acid gas, or a molecule (2 vols., see p. 36) 
of carbonic acid contains 2 vols, of oxygen. 

When one volume of carbonic acid (containing one volume of oxygen) 
is passed over heated carbon, it yields two volumes of carbonic oxide ; 
hence two volumes, or one molecule, of this gas contain one volume of 
oxygen. 

Specific gravity (to H) of C0 2 , i.e., weight of one volume, . 22 

Specific gravity (to H), or weight of one volume, of 0, . . 16 

Weight of carbon in one volume of C0 2 , " .... 6 

Hence, a molecule, 2 vols, or 44 parts by weight, of C0 2 , contains 12 parts by 
weight of carbon. 

Specific gravity (to H), or weight of one volume, of CO, = 14 

Weight of two volumes of CO, 28 

,, one volume of 0, ...... 16 

Weight of carbon in two volumes (or one molecule) of CO, 1 2 

70. The atomic weight of carbon is generally assumed to be 12, 
though, in consequence of the impossibility of determining the weight 
of one volume of carbon vapour by experiment, the chemist is compelled 
to surrender himself in this matter to the guidance of analogy and of purely 
theoretical considerations. 



Compounds of Carbon and Hydrogen. 

71. No two elements are capable of occurring in so many different 
forms of combination as carbon and hydrogen. The hydrocarbons, as 
their compounds are generally designated, include most of the inflammable 
gases which are commonly met with, and a great number of the essential 
oils, naphthas, and other useful substances. There is reason to believe 
that all these bodies, even such as are found in the mineral kingdom, 
have been originally derived from vegetable sources, and their history 
belongs, therefore, to the department of organic chemistry. The three 
simplest examples of such compounds will, however, be brought forward 
in this place, to afford a general insight into the mutual relations of these 
two important elements. Their names and composition are — 



s 



PREPARATION OF ACETYLENE. 



89 





Formulas. 
(2 vols.) 


Parts by Weight. 


C 


H 


Acetylene, . 
Marsh- gas, . 
Olefiant gas, 


C 2 H 2 
CH 4 
C 2 H 4 


24 

12 

24 


2 
4 
4 



72. Acetylene* — When very intensely heated, carbon is capable of 
combining with hydrogen to form acetylene. The requisite heat is pro- 
cured by means of a powerful galvanic battery, to the terminal wires of 
which two pieces of dense carbon are attached, and the voltaic discharge is 
allowed to take place between them in an atmosphere of hydrogen. The 
experiment possesses little practical importance, because but little acety- 
lene is formed in proportion to the force employed, but its theoretical 
interest is very great, since it is the first step in the production of organic 
substances by the direct synthesis of mineral elements ; acetylene (C 2 H 2 ) 
being convertible into olefiant gas (C 2 H 4 ), this last into alcohol (C 2 H 6 0), 
and alcohol into a very large number of organic products. 

Acetylene is constantly found among the products of the incomplete 
combustion and destructive distilla- 
tion of substances rich in carbon, 
hence it is always present in small 
quantity in coal-gas, and may be pro- 
duced in abundance by passing the 
vapour of ether through a red-hot 
tube. The character by which acety- 
lene is most easily recognised is that 
of producing a fine red precipitate in 
an ammoniacal solution of cuprous 
chloride (subchloride of copper.) 

The most convenient process for pre- 
paring a quantity of this precipitate, is 
that in which, the acetylene is produced 
by the imperfect combustion taking place 
when a jet of atmospheric air is allowed 
to burn in coal-gas. 

An adapter (A, fig. 91) is connected at 
its narrow end with the pipe supplying 
coal-gas. The wider opening is closed by a 
bung with two holes, one of which receives 
a piece of brass tube (B) about three- 
quarters of an inch wide and seven inches 
long, and in the other is inserted a glass 
tube (C) which conducts the gas to the 
bottom of a separating funnel (D). The 
lower opening of the brass tube B is closed 
with a cork, through which passes the glass tube E connected with a gas-holder or bag 
containing atmospheric air. To commence the operation, the gas is turned on 
through the tube F, and when all air is supposed to be expelled, the tube E is with- 

* Long known as Mumene, having been obtained in 1836 by the action of water upon a 
compound containing carbon and potassium, produced during the preparation of that 
metal. The name acetylene is derived from the hypothetical radical acetyle (C 2 H 3 ), to 
which acetylene bears the same relation as ethylene (C 2 H.) does to ethyle (C 2 H 5 ). 




Preparation of cuprous acetyl ide. 



90 CUPROS-ACETYLE — ARGENT- ACETYLE. 

drawn, together with its cork, and a light is applied to the lower opening of the 
brass tube, the supply of coal-gas being so regulated that it shall burn with a small 
flame at the end of the tube. A feeble current of air is then allowed to issue from 
the tube E, which is passed up through the flame into the adapter, where the jet 
of air continues to burn in the coal-gas,* and may be kept burning for hours with 
a little attention to the proportions in which the gas and air are supplied. A solu- 
tion of subchloride of copper in ammonia is poured into the separating funnel 
through the lateral opening G, so that the imperfectly burnt gas may pass through 
it, when the cuprous acetylide is precipitated in abundance. When a sufficient 
quantity has been formed, or the copper solution is exhausted, the liquid is run out 
through the stop-cock (H) on to a filter, and replaced by a fresh portion. The pre- 
cipitate may be rinsed into a flask provided with a funnel tube and delivery tube, 
allowed to subside, the water decanted from it, and some strong hydrochloric acid 
poured in through the funnel. On heating, the acetylene is evolved, and may be 
collected, either over water, or more economically in a small gas-bag, or in a mer- 
curial gas-holder. To obtain a pint of the gas, as much of the moist copper preci- 
pitate is required as will measure about six ounces after settling down. Such a 
quantity may be prepared in about six hours. 

A solution of cuprous chloride suitable for this experiment is conveniently pre- 
pared in the following manner : 500 grains of black oxide of copper are dissolved 
in seven measured ounces of common hydrochloric acid, in a flask, and boiled for 
about twenty minutes with 400 grains of copper in filings or fine turnings. The 
brown solution of cuprous chloride in hydrochloric acid thus obtained is poured into 
about three pints of water contained in a bottle ; the white precipitate (cuprous 
chloride) is allowed to subside, the water drawn off with a siphon, and the pre- 
cipitate rinsed into a twenty-ounce bottle, which is then quite filled with water and 
closed with a stopper. "When the precipitate has again subsided, the water is drawn 
off, and four ounces of powdered chloride of ammonium are introduced, the bottle 
being again filled up with water, closed and shaken. The cuprous chloride is entirely 
dissolved by the chloride of ammonium, but would be reprecipitated, if more water 
were added. When required for the precipitation of acetylene, the solution may 
be mixed with about one-tenth of its bulk of strong ammonia (*880), which may be 
poured into the separating funnel (D) before the copper solution is introduced. 
Four measured ounces of the solution are sufficient for one charge, and yield, in 
three hours, about three measured ounces of the moist precipitate. The blue solu- 
tion of ammoniacal cupric chloride, filtered from the red precipitate, may be ren- 
dered serviceable again by being shaken, in a stoppered bottle, with precipitated 
copper, prepared by reducing a solution of sulphate of copper, acidulated with hydro- 
chloric acid, with a plate of zinc. 

The red precipitate is said to consist chiefly of the oxide of a com- 
pound formed from acetylene by the substitution of Cu for H. This 
compound, C 2 CuH, has been named by Eerthelot cu2^ros-acetyle, and 
may be regarded as the radical of a series of compounds. If but little 
free ammonia be present in the solution of cuprous chloride, the pre- 
cipitate will contain the chloride of cupros-acetyle, (C 2 CuH) CI, as well 
as the oxide. 

If the acetylene copper precipitate be collected on a filter, washed, and 
dried either by mere exposure to the air, or over oil of vitriol, it will be 
found to explode with some violence when gently heated, and it is said 
that the accidental formation of this compound in copper or brass 
pipes, through which coal-gas passes, has occasionally given rise to ex- 
plosions. 

When acetylene is passed through solution of nitrate of silver, a white curdy pre- 
cipitate is formed, resembling chloride of silver in appearance, but insoluble in 
ammonia (which turns it yellow) as well as in nitric acid. It may be obtained by 
allowing the imperfectly burnt gas from the apparatus in fig. 91 to pass through 
nitrate of silver. 

* It is advisable to attach a piece of thin platinum wire to the mouth of the glass tube 
to render the flame of the air more visible. 



PROPERTIES OF ACETYLENE. 91 

When this precipitate is washed and allowed to dry, it is violently explosive if 
heated, though it may be hammered without exploding. * A minute fragment of it 
placed on a glass plate, and touched with a red-hot wire, detonates loudly and 
shatters the glass like fulminate of silver. The explosive silver compound is said 
to contain the oxide of argent-acetyle (C 2 Ag 2 H) 2 0, the chloride corresponding to it, 
(C 2 Ag 2 H) CI, being precipitated when acetylene is passed through a solution of 
chloride of silver in ammonia. In a solution of hyposulphite of gold and sodium, 
acetylene gives a yellowish very explosive precipitate. 

When potassium or sodium is heated in excess of acetylene, it is said that one 
half of the hydrogen is displaced by the metal, forming acetylide of potassium 
(C 2 HK) or of sodium (C 2 HNa), a portion of the acetylene being converted into ole- 
tiant gas (C 2 H 4 ) by combination with the displaced hydrogen. When heated to dull 
redness, sodium completely decomposes acetylene, C 2 Xa 2 being obtained. Both 
these sodium compounds are violently decomposed by water, acetylene being repro- 
duced. 

The copious formation of acetylene during the imperfect combustion of ether is 
very readily shown by introducing a few drops of ether into a test-tube, adding a 
little ammoniacal solution of cuprous chloride, "kindling the ether-vapour at the 
mouth of the tube, and inclining the latter so as" to expose a large surface of the 
copper solution, when a lerge quantity of the red cuprous acetylide is produced. If 
nitrate of silver be substituted for the copper solution, the white precipitate of oxide 
of argent-acetyle is formed abundantly. 

Acetylene has been found accompanying the vapour of hydrocyanate of ammonia 
produced by the action of ammonia on red-hot charcoal. 

Acetylene is a colourless gas having a peculiar odour, recalling that of 
the geranium, which is always perceived where coal gas is undergoing 
imperfect combustion. It burns with a very bright smoky flame. Its 
most remarkable property is that of inflaming spontaneously when brought 
in contact with chlorine. If a jet of the gas be allowed to pass into a 
bottle of chlorine, it will take fire and burn with a red flame, depositing 
much carbon. When chlorine is decanted up into a cylinder containing 
acetylene standing over water, a violent explosion immediately takes 
place, attended with a vivid flash, and separation of a large amount of 
carbon; C 2 H 2 + Cl 2 = C 2 + 2HC1. 

When acetylene is passed into water, it is absorbed in sufficient quan- 
tity to impart a strong smell to the water, and to yield a decided precipi- 
tate with ammoniacal cuprous chloride and with nitrate of silver. 

The action of heat upon acetylene is very remarkable and instructive, 
since it results in the formation of a complex body from one which is less 
complex in composition. When heated in a" glass tube for half an hour 
to the point at which the glass began to soften, it was found to be re- 
duced to one-fifth of its original volume, the greater portion of it having 
been converted into a liquid hydrocarbon, styrole, C S H S , hitherto obtained 
from the vegetable gum-resin known as storax. The reniaimng gas was 
chiefly hydrogen (a little carbon having separated) with a little olefiant 
gas. Benzole (C 6 H 6 ) has been formed, in a similar way, from three mole- 
cules of acetylene. When heated in contact with coke or iron, the bulk 
of the acetylene is decomposed into its elements. 

By suspending the acetylene copper precipitate in solution of ammonia, 
and heating with a little granulated zinc, Berthelot has induced the acety- 
lene to combine with the (nascent) hydrogen to form olefiant gas 

When a mixture of acetylene with nitrogen is acted on by a succes- 
sion of electric sparks, hydrocyanic or prussic acid (HCX) is produced 
by their direct union. 

* But if the precipitate is prepared from a slightly ammoniacal solution of nitrate <x 
silver, it explodes violently under the hammer. 



92 



OLEFIANT GAS. 



73. Olefiant gas (C 2 H 4 = 28 parts by weight = 2 vols.) — This gas 
is found in larger quantity than acetylene, among the products of the 

action of heat upon coal and 
other substances rich in carbon, 
and it is one of the most im- 
portant constituents of the illu- 
minating gases obtained from 
such materials. 

Olefiant gas may readily be 
prepared by the action of strong 
sulphuric acid (oil of vitriol, 
H 2 . SO.,) upon alcohol (spirit 
of wine C 2 H 6 0). 




Preparation of olefiant gas. 



Two measures of oil of vitriol are 
introduced into a flask (fig. 92), and 
one measure of alcohol is gradually 
poured in, the flask being agitated 
after each addition of the acid ; much 
heat is evolved, and there would be danger in mixing large volumes suddenly.* 
On applying a moderate heat, the liquid will darken in colour, effervescence will 
take place, and the gas may be collected in jars filled with water. When the 
mixture has become thick, and the evolution of the gas is slow, the end of 
the tube must be removed from the water and the lamp extinguished. Three 
measured ounces of spirit of wine generally give about 500 cubic inches of 
olefiant gas. 

The gas will be found to have a very peculiar odour, in which that of ether and 
of sulphurous acid are perceptible. One of the jars may be closed with a glass 
plate, and placed upon the table with its mouth upwards ; on the approach of a 
flame the gas will take fire, burning with a bright white flame characteristic of olefiant 
gas, and seen to best advantage when, after kindling the gas, a stream of water is 
poured down into the jar in order to displace the gas (fig. 93). 

Another jar of the gas may be well washed by 
transferring it repeatedly from one jar to another 
under water, a little solution of potash may then be 
poured into it, and the jar violently shaken, its mouth 
being covered with a glass plate ; the potash will re- 
move all the sulphurous acid, and the gas will now 
exhibit the peculiar faint odour which belongs to ole- 
fiant gas. 

The purified gas may be transferred, under water, 
to another jar, kindled, and allowed to burn out ; if 
a little lime-water be then shaken in the jar, its tur- 
bidity will indicate the presence of carbonic acid, 
which is produced, together with water, when olefiant 




burns in air 



+ 0, 



2C0 9 + 2H 9 0, 



On comparing the composition of olefiant 
gas (C 2 H 4 ) with that of alcohol (C 2 H 6 0), it 
is evident that the former may be supposed 
to be produced from the latter by the ab- 
straction of a molecule of water (H 2 0) which 
is removed by the sulphuric acid, though 
other secondary changes take place, resulting 
in the separation of carbonaceous matter and 
the production of sulphurous acid. A more 

complete explanation of the action of sulphuric acid upon alcohol must 

be reserved for the chemical history of this compound. 



Fig. 93. 



If methylated spirit be employed, the mixture will have a dark red-brown colour. 



OLEFIANT GAS. 



93 




The fra- 



Olefiant gas derives its name from its property of uniting with 
chlorine and bromine to form oily liquids, a circumstance which is 
applied for the determination of the pro- 
portion of this gas present in coal-gas, 
upon which great part of the illuminat- 
ing value of coal-gas depends. The com- 
pound with chlorine (C 2 H 4 C1 2 ) is known 
as Dutch liquid, having been discovered 
by Dutch chemists, and is remarkable 
for its resemblance to chloroform in 
odour. 

To exhibit the formation of Dutch liquid, 
a quart cylinder (fig. 94) is half filled with 
defiant gas, and half with chlorine, which is 
rapidly passed up into it, from a Dottle of the 
gas, under water. The cylinder is then closed 
with a glass plate, and supported with its 
mouth downwards under water in a separating 
funnel furnished with a glass stop-cock. The 
volume of the mixed gases begins to diminish 
immediately, drops of oil being formed upon 
the side of the cylinder and the surface of 
the water. As the drops increase, they fall to 
the bottom of the funnel. Water must be poured 
into the funnel to replace that which rises into 
the cylinder, and when the whole of the gas has 
disappeared, the oil may be drawn out of the 
funnel through the stop- cock into a test-glass, in 1 £" 

which it is shaken with a little potash to absorb any excess of chlorine 
grant odour of the Dutch liquid will then be perceived, especially on 
pouring it out into a shallow dish. 

In applying this principle to the measurement of the illuminating 
hydrocarbons in coal-gas, daylight must be excluded, or an error would 
be caused by the union of the free hydrogen with the chlorine or bro- 
mine. The bro7)iine test may be applied in the tube represented in 
fig. 95. The gas to be examined is measured over water in the divided 
limb a, with due attention to temperature and pressure ; the tube being 
held perpendicularly, the limb b will remain filled with water, so that 
gas cannot escape nor air enter. A drop or two of bromine is poured 
into this limb, which is then depressed beneath the water in the pneu- 
matic trough, and closed by the stopper c. On shaking the gas with 
the water and bromine, the latter will absorb the illuminating hydro- 
carbons, and if the tube be again opened under water, the volume of 
the gas in a will be found to have diminished, and the diminution gives 
an approximate estimate of the olefiant gas and other illuminating 
hydrocarbons. 

A very instructive experiment consists in filling a three-pint cylinder 
one-third full of olefiant gas, then rapidly filling it up, under water, 
with two pints of chlorine, closing its mouth with a glass plate, shaking 
it to mix the gases, slipping the plate aside and applying a light, 
when the mixture burns with a red flame which passes gradually 
down the cylinder, and is due to the combination of the hydro- 
gen with the chlorine, the whole of the carbon being separated in the 
solid state — 

C 2 H 4 + Cl 4 = 4HC1 + C 2 . 

When olefiant gas is subjected to the action of high temperatures, as 
by passing through heated tubes, one portion is decomposed into marsh- 
gas (CH 4 ) with separation of carbon, whilst another portion yields 
. acetylene (CH 2 ) and hydrogen ; these decompositions will be found to be 
of great importance in the manufacture of coal-gas. 




94 



MARSH-GAS. 




Fig. 96. 



The action of heat upon olefiant gas is most conveniently shown by exposing it to 
the spark from an induction coil. 

The gas is confined in a tube (A, fig. 96) which is placed 
in a cylindrical jar (B) containing mercury. Through the 
mercury passes a copper wire (C) thrust through a glass 
tube (D) to insulate it from the mercury ; this wire is con- 
nected with one of the wires (E) from the induction coil, 
whilst the other (F) is allowed to dip into the mercury con- 
tained in the cylinder. On putting the coil in action (with 
two or three cells of Grove's battery), the spark will pass 
between the extremity (C) of the insulated copper wire and 
the surface of the mercury in the tube, decomposing the ole- 
fiant gas in its passage, and causing a separation of carbon, 
which sometimes forms a conducting communication, and 
allows the current to pass without a spark. This may be 
obviated by reversing the current, or by gently shaking the 
tube. 

The olefiant gas will expand to nearly twice its former 
volume, so that the tube will gradually rise in the mercury, 
but the same distance may always be maintained for the 
passage of the spark. 

To show the production of acetylene, another arrangement will be found con- 
venient (fig. 97). A globe 
with four necks is employed ; 
through two of these necks 
are passed, air-tight with per- 
forated corks, the copper 
wires connected with the in- 
duction coil. A third neck 
receives a tube, conveying 
olefiant gas from a gas-hold- 
er, whilst from the fourth 
proceeds a tube dipping to 
the bottom of a small cylin- 
der. When the whole of the 
air has been displaced by ole- 
fiant gas, a solution of sub- 
chloride of copper in am- 
monia is poured, into the 
cylinder, and the gas allowed 
to bubble through it, when 
the absence of acetylene will 
be shown by there being no 
red compound formed. As 
soon, however, as the spark 
is passed, the red precipitate 
will appear, and, in a very 
few minutes, a large quantity 
will be deposited. Coal-gas 
may be employed instead of 
olefiant gas, but of course less 
of the copper- compound will 
be obtained. 




Fig. 97. 



-Preparation of cuprous acetylide from 
olefiant gas. 



74. Marsh -gas, or light carburetted hydrogen (CH 4 =16 parts by 
weight = 2 vols.) — Unlike acetylene and olefiant gas, this hydrocarbon is 
found in nature, being produced wherever vegetable matter is undergoing 
decomposition in the presence of moisture. The bubbles rising from 
stagnant pools, when collected and examined, are found to contain marsh- 
gas mixed with carbonic acid, and there is reason to believe that these 
two gases represent the principal forms in which the hydrogen and 
oxygen respectively were separated from wood during the process of its 
conversion into coal. This would account for the constant presence of 



PREPARATION OF MARSH- GAS. 95 

this gas ill the coal-formations, where it is usually termed fire-damp. It 
is occasionally found pent up under pressure between the layers of coal, 
and the pores of the latter are sometimes so full of it that it may be seen 
rising in bubbles when the freshly hewn coal is thrown into water. Per- 
haps a similar origin is to be ascribed to the liquid hydrocarbons chemi- 
cally similar to marsh-gas, which are found so abundantly in Pennsylvania 
and Canada, and are known by the general name of petroleum. 

Marsh-gas is obtained artificially by the following process : — 

500 grains of dried acetate of soda are finely powdered, and mixed, in a mortar, 
with 200 grains of solid hydrate of potash, and 300 grains of powdered quicklime (or 
with 500 grains of the mixture of hydrate of lime and hydrate of soda, which is sold 
as soda-lime). The mixture is heated in a Florence flask (or better, a copper tube, 
for the alkali corrodes the glass), and the gas collected over water (fig. 98). 




Fig. 98. — Preparation of marsh-gas. 



The decomposition will be evident from the following ecpuation 



Acetate of soda. 



NaHO = 

Caustic soda. 



.Na 2 . C0 2 + 
Carb. of soda. 



CH 4 



The marsh-gas will be easily recognised by its burning with a pale 
illuminating flame, far inferior in brilliancy to those of olefiant gas and 
acetylene, but unattended with smoke. 

The properties of this gas deserve a careful study, on account of the 
frequent fatal explosions to which it gives rise in coal-mines, where it is 
often found accumulated under pressure, and discharging itself with con- 
siderable force from the fissures or blowers made in hewing the coal. 
Marsh-gas has no characteristic smell like coal-gas, and the miner thence 
receives no timely warning of its presence ; it is much lighter than air 
(sp. gr. 0*5596), and therefore very readily diffuses* itself (page 16) 
through the air of the mine, with which it forms an explosive mixture as 
soon as it amounts to one-eighteenth ef the volume of the air. The gas 
issuing from the blower would burn quietly on the application of a light, 
since the marsh-gas is not explosive unless mixed with the air, when a 
large volume of the gas is burnt in an instant, causing a sudden evolution 

* Ansell's fire-damp indicator is an apparatus in which the high rate of diffusion of 
marsh-gas is taken advantage of in order to detect its presence in the air of mines. The 
experiment described at page 18 illustrates its principle. 



96 EXPLOSION OF MARSH-GAS WITH AIR. 

of a great deal of heat, and a consequent sudden expansion or explosion 
exerting great mechanical force. The most violent explosion takes place 
when one volume of marsh-gas is mixed with two volumes of oxygen, 
since this quantity is exactly sufficient to effect the complete combustion 
of the carbon and hydrogen of the gas, and therefore to evolve the greatest 
amount of heat : CH 4 + O i — C0 2 + 2H 2 0. The calculated pressure 
exerted by the exploding mixture of marsh-gas and oxygen amounts to 
37 atmospheres, or 555 lbs. upon the square inch. Since air contains one- 
fifth of its volume of oxygen, it would be necessary to employ ten 
volumes of air to one volume of marsh-gas in order to obtain perfect com- 
bustion, but the explosion will be much less violent on account of the 
presence of the eight volumes of inert nitrogen, the calculated pressure 
exerted by the explosion being only 14 atmospheres, or 210 lbs. on the 
square inch. Of course, if more air is employed, the explosion will be 
proportionally weaker, until, when there are more than eighteen volumes 
of air to each volume of marsh-gas, the mixture will be no longer explosive, 
but will burn with a pale flame around a taper immersed in it. The car- 
bonic acid resulting from the explosion is called by miners the after-damp, 
and its effects are generally fatal to those who may have escaped death 
from the explosion itself. 

Fortunately, marsh-gas requires a much higher temperature to inflame 
it than most other inflammable gases ; thus a solid body at an ordinary 
red heat does not kindle the gas, contact with flame, or with a body 
heated to whiteness, being required to ignite it. 

If two strong gas cylinders be filled, respectively, with mixtures of 2 vols, hydrogen 
with 1 vol. oxygen, and of 1 vol. marsh-gas and 2 vols, oxygen, it will be found, on 
holding them with their mouths downwards, and inserting a red-hot iron bar (fig. 99), 

that the marsh -gas mixture will not explode, but 
if the bar be transferred at once to the hydrogen 
mixture, explosion will take place. A lighted 
taper may then be used to explode the marsh-gas 
and oxygen. 

Coal-gas, although answering very well for many 
illustrations of the properties of marsh-gas, cannot 
be used in this experiment, since some of its con- 
, . stituents inflame at a far lower temperature. 

In consequence of the high temperature 
required to inflame the mixture of marsh- 
gas and air, it is necessary that the mixture 
be allowed to remain for an appreciable 
time in contact with the flame before its particles are raised to the 
igniting point. Tt was on this principle that Stephenson's original safety 
lamp was constructed, the flame being surrounded with a tall glass 
chimney, the rapid draught through which caused the explosive mixture 
to be hurried past the flame without igniting. 

To illustrate this, a copper funnel holding about two quarts (fig. 100) is employed, 
the neck of which has an opening of about \ inch in diameter. The funnel being 
placed mouth downwards in the pneumatic trough, the orifice is closed with the 
finger, and half a pint of coal-gas passed up into the funnel. The latter is now 
raised from the water, so that it may become entirely filled with air. By depressing 
the funnel to a considerable depth in the water, the aperture being still closed by 
the finger, the mixture will be confined under considerable pressure, and if a lighted 
taper be held to the aperture, and the finger removed, it will be found that the 
mixture sweeps past the flame without exploding, until the water has reached the 




PRINCIPLE OF SAFETY LAMPS. 



97 



same level in the funnel as in the trough, when the gas comes to rest and explodes 
with great violence. 





Fig.101. — Davy lamp. 



Fig. 100. 

Davy's safety lamp (fig. 101) is an application of the principle that 
ignited gas (flame) is extinguished by contact with a 
large surface of a good conductor of heat, such, as 
copper or iron. 

If a thin copper wire be coiled round into a helix, and care- 
fully placed over the wick of a burning taper (fig. 102), the flame 
will be at once extinguished, its heat being so rapidly trans- 
mitted along the wire that the temperature falls below the 
point at which the combustible gases enter into combination 
with oxygen, and therefore the combustion ceases. If the coil 
be heated to redness in a spirit-lamp flame before placing it 
over the wick, it will not abstract the heat so readity, and will 
not extinguish the flame. If a copper tube were substituted 
for the coiled wire, the same result would be obtained, and by employing a number 
of tubes of very small diameter, so that the metallic surface may be very large in 
proportion to the volume of ignited gas, the most energetic combustion may be 
arrested, as in the case of Hemming 's safety jet, which 
consists of a brass tube tightly stuffed with thin copper 
wires so as to leave very narrow passages, thus rendering 
it impossible for the oxy hydrogen flame at the jet to pass 
back and ignite the mixture in the reservoir. 

It is evident that the exposure of a large extent of cool- 
ing surface to the action of the flame, may be effected 
either by increasing the length or by diminishing the 
width of the metallic tubes, so that wire gauze, which may 
be regarded as a collection of very short tubes, will form 
an effectual barrier to flame, provided that it has a suffi- 
cient number of meshes to the inch. 

If a piece of iron wire gauze, containing about 800 meshes to the square inch, be 
depressed upon a flame, it will extinguish that portion with which it is in contact, 
and the combustible gas which escapes through the gauze may be kindled by a 
lighted match held on the upper side. By holding the gauze two or three inches 
above a gas jet, the gas may be lighted above it without communicating the flame 
to the burner itself. 

When blazing spirit is poured upon a piece of wire gauze (fig. 103), the flame will 
remain upon the gauze, and the extinguished spirit will pass through. A little 
benzole or turpentine may be added to the spirit, so that its flame may be more visible 
at a distance. 

The safety lamp is an oil lamp, the flame of which is surrounded by a 
cage of iron wire gauze, having 700 or 800 meshes in the square inch, 
and made double at the top where the heat of the flame chiefly plays. 
This cage is protected by stout iron wires attached to a ring for suspend- 

G 




98 



USE OF THE DAVY LAMP. 




ing the lamp. A brass tube passes up through the oil reservoir, and in 
this there slides, with considerable friction, a wire bent at the top, so that 

the wick may be trimmed without taking 

off the cage. 

If this lamp be suspended in a large jar, closed 
at the top with a perforated wooden cover (A, 
fig. 104), and having an aperture (B) below, 
through which coal-gas may be admitted, the 
lamp will burn, of course in the ordinary way ; 
but if the gas be allowed to pass slowly into the 
jar, the flame will be seen to waver, to elongate 
itself very considerably, and will be ultimately 
extinguished, when the wire cage will be seen to 
be filled with a mixture of coal-gas and air burn- 
^" ' ing tranquilly within the gauze, which prevents 

the flame from passing to ignite the explosive atmosphere surrounding the lamp ; 
that an explosive mixture really fills the jar may be readily ascertained by in- 
troducing, through an aperture (C) in the cover, the 
unprotected flame of a taper, when an explosion will 
take place. 

This experiment illustrates the action of the Davy 
lamp in a mine which contains fire-damp, and makes it 
evident that this lamp would afford complete protection 
if carefully used. It would obviously be unsafe to allow 
the lamp to remain in the explosive mixture when the 
cage is filled with flame, for the gauze would either 
become sufficiently heated to kindle the surrounding gas, 
or would be oxydised and eaten into holes, which would 
allow the passage of the flame. Nor should the lamp 
be exposed to a very strong current, which might pos- 
sibly be able to carry the flame through the meshes. 



The great defect of the Davy lamp is that it 
Fig. 104. does not afford more than a glimmering light, so 

that even if the miners were prohibited from em- 
ploying any candles, they would (and experience has proved that they do) 
remove the wire cage at all risks. The lamp has been modified so as par- 
tially to remove this defect, by substituting glass or talc for some portions 
of the wire gauze. It is now usual, however, to employ the Davy lamp 
merely in order to test the state of the air in the different parts of the 
mine ; for this purpose the firemen descend before the commencement 
of work every morning, and examine with their safety lamps every portion 
of the mine, giving warning to the miners not to approach those parts in 
which any accumulation of fire-damp (or technically, " sulphur") is per- 
ceived. The miners then work with naked candles, and it appears to be 
not unusual to see a blue flame (or corpse light) playing around the 
candles, so that the miners may become accustomed to regard with little 
concern the very indication which shows that the quantity of fire-damp is 
only a little below that required to form an explosive mixture. When- 
ever naked flames are used in the mine there must always be great risk ; 
in most seams of coal there are considerable accumulations of fire-damp ; 
when a fissure is made, the gas escapes very rapidly from the blower, and 
the air in its vicinity may soon become converted into an explosive mix- 
ture. In mines where small quantities of fire-damp are known to be 
continually escaping from the coal, ventilation is depended upon in order 
to dilute the gas with so large a volume of air that it is no longer explo- 
sive, and finally to sweep it out of the mine ; but it has occasionally 
happened that the ventilation has been interfered with by a door having 




ILLUMINATING FLAMES. 99 

been left open in one of the galleries, or by a passage having been 
obstructed through the accidental falling in of a portion of the coal, and 
an explosive mixture has then been formed. 

Structure of Flame. 

75. The consideration of the structure and properties of ordinary 
flames is necessarily connected with the history of defiant gas and marsh- 
gas. Flame may be defined as gaseous matter, heated to the temperature 
at which it becomes visible, or emits light. Solid particles begin, for the 
most part, to emit light when heated to about 1000° F. ; but gases, on 
account of their greater expansibility, must be raised to a far higher 
temperature, and hence the point of visibility is seldom attained, except 
by gases which are themselves combustible, and therefore capable of 
producing, by their own combination with atmospheric oxygen, the requi- 
site degree of heat. The presence of a combustible gas (or vapour), 
therefore, is one of the conditions of the existence of flame ; a diamond, 
or a piece of thoroughly carbonised charcoal, will burn in oxygen with 
a steady glow, but without flame, since the carbon is not capable of con- 
version into vapour, while sulphur burns with a voluminous flame, in 
consequence of the facility with which it assumes the vaporous condition. 
It will be observed, moreover, that in the case of a non-volatile combus- 
tible, the combination with oxygen is confined to the surface of contact, 
whilst in the flame of a gas or vapour, the combustion extends to a con- 
siderable depth, the oxygen intermingling with the gaseous fuel. 

Flames may be conveniently spoken of as simple or compound, accord- 
ingly as they involve- one or more phenomena of combustion ; thus, for 
example, the flames of hydrogen and carbonic oxide are simple, whilst 
those of marsh-gas and olefiant gas are compound, since they involve both 
the conversion of hydrogen into water and of carbon into carbonic acid. 

It is obvious that simple flames must be hollow in ordinary cases, such 
as that of a gas issuing from a tube into the air, the hollow being occu- 
pied by the combustible gas to which the oxygen does not penetrate. 

All the flames which are ordinarily turned to useful account are com- 
pound flames, and involve several distinct phenomena. Before examining 
these more particularly, it will be advantageous to point out the conditions 
which regulate the luminosity of flames. 

In order that a flame may emit a brilliant light, it is essential that it 
should contain particles which, either from their own nature, or from the 
conditions under which they are placed, do not admit of indefinite ex- 
pansion by the heat of the flame, but are capable of being heated to 
incandescence. Thus, the flame of the oxy hydrogen blowpipe (p. 38) emits 
a very pale light, but if the mixture of oxygen and hydrogen be restrained 
from expanding when fired, as in the Cavendish eudiometer (p. 32), it 
gives a bright flash ; or if the flame be directed upon some solid body 
little* affected by heat, such as lime, the light is very intense. 

Phosphorus and arsenic burn with very luminous flames, in consequence 
of the formation of very dense vapours of phosphoric and arsenious acids 
during the combustion ; the density of the vapours being here attended 
With the same result as that produced by the restrained expansion of the 
steam formed in the Cavendish eudiometer. 

It is not necessary that the incandescent matter should be a product 
of the combustion ; any extraneous solid in a finely divided state will 



100 



STRUCTURE OF FLAME. 




Fig. 105. 



confer illuminating power upon a flame. Thus, the flame of hydrogen 
may he rendered highly luminous hy "burning a piece of phosphorus in its 
vicinity, so that the clouds of phosphoric acid may pass 
through the flame, or by blowing a little very fine char- 
coal powder into it, from the bottle represented in 
fig. 105. 

The luminosity of all ordinary flames is due to the 
presence of highly heated carbon in a state of very 
minute division, and it remains to consider the changes 
by which this finely divided carbon is separated in the 
flame. 

A candle, a lamp, and a gas-burner, exhibit contriv- 
ances for procuring light artificially in different degrees 
of complexity, the candle being the most complex of the three. When a 
new candle is lighted, the first portion of the wick is burnt away until the 
heat reaches that part which is saturated with the wax or tallow 
of which the candle is composed ; this wax or tallow then under- 
goes destructive distillation, yielding a variety of products, among 
which olefiant gas is found in abundance. The flame furnished 
by the combustion of these products melts the fuel around the 
base of the wick, through which it then mounts by capillary 
attraction, to be decomposed in its turn, and to furnish fresh gases 
for the maintenance of the flame. In a lamp, the fuel being 
liquid at the commencement, the process of fusion is dispensed 
with ; and in a gas-burner, where the fuel is supplied in a gaseous 
form, the process of destructive distillation has been already 
carried on at a distance. It will be seen, however, that the final 
result is similar in all three cases, the flame being maintained by 
such gases as acetylene, marsh-gas, and olefiant gas, arising from 
Fig. 106. ^ e destructive distillation of wax, tallow, oil, coal, &c. 

On examining an ordinary flame, that of a candle, for instance, it is 
seen to consist of three concentric cones (fig. 106), the innermost, around 

the wick, appearing almost black, the 
jjL next emitting a bright white light, and 

m .the outermost being so pale as to be 

scarcely visible in broad daylight. 

The dark innermost cone consists merely 
of the gaseous combustible to which the 
air does not penetrate, and which is there- 
fore not in a state of combustion. 




The nature of this cone is easily shown by- 
experiment: a strip of cardboard held across 
the flame near its base will not burn in the 
centre where it traverses the innermost cone ; a 
Fig. 107. piece of wire gauze depressed upon the flame 

near the wick (fig. 107) will. allow the passage 
of the combustible gas, which may be kindled above it. The gas may be conveyed 
out of the flame by means of a glass tube inserted into the innermost cone, and may 
be kindled at the other extremity of the tube, which should be inclined downwards 

A piece of phosphorus in a small spoon held in the interior of the flame of a spirit- 
lamp, will melt and boil, but will not burn unless it be removed from the flame, and 
may then be extinguished by replacing it in the flame. 

The combustible gas from the interior of a flame may be collected in a flask 
(fig. 109) furnished with two tubes, one of which (A) is drawn out to a point for 



EXPERIMENTS ON FLAME. 



101 



insertion into the flame, whilst the other (B), which passes to the bottom of the flask, 
is bent over and prolonged by a piece of vulcanised tubing, so that it may act as a 




Fig. 108. 

siphon. The flask is filled up with water, the jet inserted into the interior of a flame, 
and the siphon set running by exhausting it with the mouth. As the water flows 
out through the siphon, the gas is drawn into the flask, and 
after removing the tube from the flame, the gas may be ex- 
pelled by blowing down the siphon tube, and may be burnt 
at the jet. When a candle is used for this experiment, some 
solid products of destructive distillation will be found con- 
densed in the flask. 




In the second or luminous cone, combustion is 
taking place, but it is by no means perfect, being 
attended by the separation of a quantity of carbon, 
which confers luminosity upon this part of the 
flame. The presence of free carbon is shown by de- Fig. 109. 

pressing a piece of porcelain upon this cone, when a 
black film of soot is deposited. The liberation of the carbon is due to 
the decomposition of the olefiant gas and similar hydrocarbons by the 
heat, which separates the carbon from the hydrogen, and this latter, 
undergoing combustion, evolves sufficient heat to raise the separated car- 
bon to a white heat, the supply of air which penetrates into this portion 
of the flame being insufficient to effect the combustion of the whole of 
the carbon. 

Some very simple experiments will illustrate the nature of the luminous portion of 
flame. 





110. 



Fig. 111. 



Oyer an ordinary candle flame (fig. 110) a tube may be adjusted so as to convey 
the finely divided carbon from the luminous part of the flame into the flame of 



102 



EXPERIMENTS ON FLAME. 




Fig. 112. 



hydrogen, which will thus be rendered as luminous as the candle flame, the dark 
colour of the carbon being apparent in its passage through the tube. 

A bottle furnished with two straight tubes (fig. Ill) is connected with a reservoir 

of hydrogen. One of the tubes is provided with 
a small piece of wider tube containing a tuft of 
cotton wool. On kindling the gas at the orifice 
of each tube, no difference will be seen in the 
flames until a drop of benzole (C 6 H 6 ) is placed 
upon the cotton, when its vapour, mingling with 
the hydrogen, will furnish enough carbon to ren- 
der the flame brilliantly luminous. 

Fig. 112 shows a more convenient apparatus 
for the same purpose ; the hydrogen being passed 
in through c, burns from the tube a with a non- 
luminous flame, and from the tube b, after passing 
over a piece of cotton, moistened with benzole, 
with a luminous flame. 

The pale outermost cone, or mantle, of 
the flame, in which the separated Carbon 
is finally consumed, may be termed the 
cone of perfect combustion, and is much 
thinner than the luminous cone, the sup- 
ply of air to this external shell of flame 
being unlimited, and the combustion 
therefore speedily effected. 

The mantle of the flame may be rendered more visible by burning a little sodium 
near the flame, when the mantle is tinged strongly yellow. 

By means of a siphon about one-third of an inch in diameter (fig. 113), the nature 
of the different portions of an ordinary candle flame may be very elegantly shown. 
If the orifice of the siphon be brought just over the extremity of the wick, the com- 
bustible gases and vapours will pass through it, and 
may be collected in a small flask, where they can be 
kindled by a taper. On raising the orifice into the 
luminous portion of the flame, voluminous clouds of 
black smoke will pour over into the flask, and if the 
siphon be now raised a little above the point of the 
flame, carbonic acid can be collected in the flask, and 
may be recognised by shaking with lime-water. 

The reciprocal nature of the relation between the 
conibustible gas and the air which supports its com- 
bustion may be illustrated in a striking manner by 
burning a jet of air in an atmosphere of coal-gas. 
Fi S- H3. j^ quart glass globe with three necks is connected 

at A (fig 114) with the gas-pipe by a vulcanised tube. The second neck (B), at the 
upper part of the globe, is connected by a short piece of vulcanised tube with a piece 
of glass tube about | inch wide, from which the gas may be burnt. Into the third 
and lowermost neck is inserted, by means of a cork, a thin brass tube, C (an old 
cork-borer), about ^ inch in diameter. "When the gas is turned on, it may be lighted 
at the upper neck ; and if a lighted match be then quickly thrust up the tube C, the 
air which enters it will take fire and burn inside the globe. 

A very inexpensive apparatus for this purpose may be constructed from a common 
Florence oil-flask. By applying a blowpipe flame at A (fig. 115), so as to heat to 
whiteness a spot as large as a threepenny-piece, and quickly blowing into the neck 
of the flask, the heated portion of the glass may be made to "bulge out. A similar 
protuberance is then to be formed at B. A sharp-pointed flame is directed upon A, 
and the glass burst by blowing into the flask whilst it is still exposed to the flame. 
By fusing the edges of the hole thus produced, and turning them outwards with the 
end of a file, a short neck may be formed capable of receiving a cork. "When this 
is cool, it is closed with a cork, and a second similar neck is produced at B. 

From this review of the structure of flame, it is evident that, in order 
to secure a flame which shall be useful for illumination, attention must 




GAS-BURNERS, 



103 



be paid to the supply of oxygen (or air), and to the composition of the 
fuel employed. The use of the chimney of an Argand burner (fig. 116) 





Fig. 114. — Air burning in 
coal-gas. 



Fig. 115.— To make a three necked-ilask. 




Fig. 116. — Argand burner. 



affords an instance of the necessity for attention to the proper supply of 
air. Without the chimney, the flame is red at the edges and smoky, for 
the supply of air is not sufficient to consume 
the whole of the carbon which is separated, and 
the temperature is not competent to raise it to 
a bright white heat, defects which are remedied 
as soon as the chimney is placed over it, and 
the rapidly-ascending heated column of air draws 
in a liberal supply beneath the burner, as indi- 
cated by the arrows. 

By using two chimneys, and causing the air 
to pass down between them, so as to be heated 
to about 500° F. before reaching the flame, an 
equal amount of light may be obtained from a 
much smaller supply of gas. 

The smokeless gas-burners employed in labo- 
ratories and kitchens exhibit the result of "mix- 
ing the gas with a considerable proportion of air before burning it, the 
luminous part of the flame then entirely disappearing, with great aug- 
mentation of the temperature of the flame, since 
the carbon is burnt simultaneously with the hydro- 
gen. 

The most efficient burner of this kind (Bunsen's burner, 
fig. 117) is that in which the gas is conveyed into a wide 
tube, at the base of which there are four large holes for the 
admission of air. "When a good supply of gas is turned 
on, a quantity of air is drawn in through the lower aper- 
tures, and the mixture of air and gas may be kindled at 
the orifice of the wide tube, its rapid motion preventing the 
flame from passing down within the tube. This tube is 
sometimes surmounted by a rosette burner to distribute the 

flame. By closing the air-holes with the fingers, a luminous flame is at once pro- 
duced. 

The principle of this burner has been applied for testing the illuminating value of 
gas, by measuring the quantity of air which must be supplied to a flame consuming 
a given quantity of gas, in order to destroy the luminosity, the illuminating value 
being proportional to the quantity of air which is necessary for this purpose. 




Fig. 117. — Bunsen's 
burner. 



104 



COMPOSITION OF ILLUMINATING FUELS. 




Fig. 118.— Gauze 
burner. 



The gauze burner (fig. 118) consists of an open cylinder surmounted by wire gauze. 
When this is placed over the gas burner, a supply of air is drawn in at the bottom by 
the ascending stream of gas, and the mixture burns above 
the gauze Avith a very hot smokeless flame, the metallic 
meshes preventing the flame from passing down to the gas 
below. 

The luminosity of a flame is materially affected by 
the pressure of the atmosphere in which it burns, a 
diminution of pressure causing a loss of illuminating 
power. If the light of a given flame burning in the 
air when the barometer stands at 30 inches be repre- 
sented by 100, each diminution of one inch in the 
height of the barometer will reduce the luminosity 
by five ; and conversely, when the barometer rises one inch, the lumino- 
sity will be increased by five. This is not due to any difference in the 
rate of burning, which remains pretty constant, but to the more complete 
interpenetration of the rarefied air and the gases composing the flame, 
giving rise to the separation of a smaller quantity of incandescent carbon. 
In air at a pressure of 120 inches of mercury, the flame of alcohol is 
highly luminous, the high density of the air discouraging the intermixture 
of the flame-gases with it, and thus allowing the separation of a portion 
of carbon. 

In considering the influence exerted by the composition of the fuel 
upon the character of its flame, it will be necessary to bear in mind that 
some kinds of fuel consist of carbon and hydrogen only, whilst others 
contain a considerable proportion of oxygen. 

The following table exhibits the composition of some of the principal 
substances concerned in producing ordinary illuminating flames : — 



Fuel. 


Formula. 


Carbon. 


Hydrogen. 


Oxygen. 


Marsh-gas, . . 


CH 4 


30 


10 




Olefiant gas, 






C 2 H 4 


60 


10 




Paraffine, 






C A .H2#4.2 


30 


10 




Turpentine, . 






CioH 16 


75 


10 




Benzole, 






• C 6 H 6 


120 


10 




Wax, . 






^46^92^2* 


60 


10 


35 


Stearine, 






^57-"- 110^6 


62'1 


10 


8 7 


Oleine, 






CWHio^e 


65-8 


10 


9-2 


Alcohol, 






C 2 H 6 


40 


10 


27 


Wood naphtha, 






CH 4 


30 


10 


40 



It may be stated generally that when the number of atoms of carbon 
is less than half that of hydrogen, the flame will be free from smoke, as 
in the case of marsh-gas. When there are half as many atoms of carbon 
as of hydrogen, as in olefiant gas, the flame is very liable to smoke, unless 
managed with great judgment. Those hydro-carbons which contain, like 
turpentine and benzole, a larger proportion of carbon than this, always 
burn with much smoke, and require special contrivance to render them 
applicable for illuminating purposes. Thus, camphine (turpentine) must 
be burnt in lamps with tall narrow chimneys of peculiar construction to 

* This is the composition of myricine, which forms the greater part of bees' wax. 



THE BLOWPIPE FLAME. 



105 




Fig. 119. 



afford a strong current of air. Benzole (coal-naphtha) vapour must be 
mixed with air if it is required to burn with a smokeless flame. 

If a piece of cotton wool, moistened with benzole, be placed in a flask provided 
with two tubes (fig. 119), it will be found, on gently warming the flask by dipping 
it into hot water, and blowing through one of the tubes, that the mixture of benzole 
vapour and air issuing from the other tube will burn with a smokeless bright flame. 

If coal-gas, which is essentially a mixture of hydrogen, marsh-gas, and 
olefiant gas, and generally contains rather too much hydrogen in propor- 
tion to its carbon, be enriched with carbon by 
passing over benzole (light coal naphtha), it burns 
with a far more luminous flame (naphtlialised gas). 

When the fuel contains oxygen, the carbon may 
exist in larger proportion to the hydrogen without 
giving rise to the production of smoke, since this 
oxygen will dispose of a portion of the carbon 
during the combustion. Thus, wax is much less 
liable to smoke than olefiant gas, although containing 
the same proportions of carbon and hydrogen, 
whilst stearine (the chief part of tallow) and oleine 
(forming the bulk of oils) may be burnt in ordi- 
nary candles and lamps, although still richer in 
carbon, because they contain more oxygen also. 

Alcohol yields a flame of no illuminating value, although it contains 
more carbon in proportion to its hydrogen than is present in marsh-gas, 
because its oxygen helps to consume the carbon during the combustion, 
and prevents it from separating in the incandescent state. By adding 
about one-tenth of its bulk of benzole or turpentine, however, alcohol 
may be made to burn with a brilliant flame. 

76. The blowpipe Jiame, — The principles already laid down will 
render the structure of the blowpipe flame easily intelligible. It must 
be remembered that in using the blowpipe, the stream of air is not pro- 
pelled from the lungs of the operator (where a great part of its oxygen 
would have been consumed), but simply from the mouth, by the action 
of the muscles of the cheeks. The first apparent effect upon the flame 
is entirely to destroy its luminosity, the free supply of air effecting the 
immediate combustion of the carbon. The size of the flame, moreover, is 
much diminished, and the combustion being concentrated into a smaller 
space, the temperature must be much 
higher at any given point of the 
flame. In structure, the blowpipe 
flame is similar to the ordinary 
flame, consisting of three distinct 
cones, the innermost of which (A, 
fig. 120) is filled with the cool 
mixture of air and combustible 
gas. The second cone, especially 
at its point (E), is termed the 




Fig. 120.— Blowpipe Flame. 



reducing flame, for the supply of oxygen at that part is not sufficient 
to convert the carbon into carbonic acid, but leaves it as carbonic 
oxide, which speedily reduces almost all metallic oxides placed in that 
part of the flame to the metallic state. The outermost cone (0) is 
called the oxidising flame, for there the supply of oxygen from the sur- 



106 



HOT- BLAST BLOWPIPE. 



rounding air is unlimited, and any substance prone to combine with, 
oxygen at a nigh temperature is oxidised when exposed to the action of 
that portion of the flame; the hottest point of the blowpipe flame, 
where neither fuel nor oxygen is in excess, appears to be a very little 
in advance of the extremity of the second (reducing) cone. The differ- 
ence in the operation of the two flames is readily shown by placing a 
little red lead (oxide of lead) in a shallow cavity scooped upon the 
surface of a piece of charcoal (fig. 121), and directing the flames upon 
it in succession; the inner flame will reduce a globule of metallic 
lead, which may be reconverted into oxide by exposing it to the outer 




Fig. 121. — Reduction of metals on charcoal. 

flame.* The immense service rendered by this instrument to the chemist 
and mineralogist is well known. 

By forcing a stream of oxygen through a flame from a gas-holder 
or bag, an intensely hot blowpipe flame is obtained, in which pipe-clay 
and platinum may be melted, and iron burns with great brilliancy (see 
fig. 56). 

Fletcher's hot-blast blowpipe (fig. 122), produces a much, higher temperature than 
the ordinary blowpipe. Coal-gas is supplied through the tube g, and is kindled at 

the Bunsen burners b h and at the orifice /, the 
supply to the former being regulated by the stopcock 
c, and to the latter by the stopcock d. The flames 
of the Bunsen burners heat the spiral copper tube 
e to redness, so that the air blown in through the 
flexible tube a is strongly heated before being pro- 
jected into the flame through a blowpipe jet at /. 
Thin platinum wires melt easily in this flame, and 
thin iron wires burn away rapidly. 

77. Determination of the composition of 
gases containing carbon and hydrogen. — In 
order to ascertain the proportions of carbon 
and hydrogen present in a gas, a measured 
volume of the gas is mixed with an excess 
of oxygen, the volume of the mixture carefully noted, and explosion deter- 
mined by passing the electric spark ; the gas remaining after the explosion 
is measured and shaken with potash, which absorbs the carbonic acid, 
from the volume of which the proportion of carbon may be calculated. 
For example, 

0*4 cubic inch of marsh-gas, mixed with 
1*0 „ oxygen, and exploded, left 

0* 6 „ gas ; shaken with potash 

it left 0-2 „ oxygen. 

* By directing the reducing flame upon the metallic oxide in the cavity, and allowing 
the oxidising flame to sweep over the surface of the charcoal, as shown in the figure, a 
yellow incrustation of oxide of lead is formed upon the surface of the charcoal, which 
affords additional evidence of the nature of the metal. 




Fig. 122. --Hot-blast blowpipe. 



PRODUCTS OF DISTILLATION OF COAL. 



107 



Showing that 04 cubic inch of carbonic acid had been produced. This 
quantity of carbonic acid would contain - 4 cubic inch of oxygen. De- 
ducting this last from the total amount of oxygen consumed (0*8 cubic 
inch), we have 0*4 cubic inch for the volume of oxygen consumed by the 
hydrogen. Now, 0*4 cubic inch of oxygen would combine with 0*8 cubic 
inch of hydrogen, which represents therefore the amount of hydrogen in 
the marsh-gas employed. It has thus been ascertained that the marsh- 
gas contains twice its volume of hydrogen. 



Sp. Gr. (to H) or weight of 1 volume of marsh-gas, 

Weight of 2 volumes (one molecule), . 
2 volumes of marsh-gas contain 4 volumes H, weighing 

2 volumes of marsh-gas contain x volume C, weighing 



8 

16 

4 

12 



For the purpose of illustration, the analysis of marsh-gas may be effected in a Ure's 
eudiometer (fig. 123), but a considerable excess of oxygen should be added to mode- 
rate the explosion. The eudiometer having been filled 
with water, 0*1 cubic inch of marsh-gas is introduced 
into it, as described at p. 34, and having been transferred 
to the closed limb and accurately measured after equal- 
ising the level of the water, the open limb is again filled 
up with water, the eudiometer inverted in the trough, 
and 1 "2 cubic inch of oxygen added ; this is also trans- 
ferred to the closed limb and carefully measured. The 
electric spark is passed through the mixture (see p. 
34), the open limb being closed by the thumb. The 
level of the water in both limbs is then equalised, and 
the volume of gas measured. The open limb is filled 
up with a strong solution of potash, and closed by 
the thumb, so that the gas may be transferred from 
the closed to the open limb and back, until its volume 
is no longer diminished by the absorption of carbonic acid, 
oxygen having been measured, the calculation is effected as above described. 

The results are more exact when the eudiometer is filled with mercury instead of 
water. 




Fig. 123. 
Sij)Uon eudiometer. 

The volume of residual 



Coal-Gas. 

78. The manufacture of coal-gas is one of the most important appli- 
cations of the principle of destructive distillation, and affords an ex- 
cellent example of the tendency of this process to develope new arrange- 
ments of the elements of a compound body. The action of heat upon 
coal, in a vessel from which air is excluded, gives rise to the production 
of a very large number of compounds containing some two or more of 
the five elements of the coal, in different proportions, or in different 
forms of arrangement. Although no clue has yet been obtained to indi- 
cate the true arrangement of these elements in the original coal (or, 
as it is termed, the constitution of the coal), it is certain that these 
various compounds do not exist in it before the application of heat, but 
are really the results of its action, that they are indeed products and 
not educts. 

The most important forms assumed by the carbon and hydrogen when 
coal is strongly heated, are, — 

(Hydrogen, 
Marsh-gas, CH 4 
Olefiant gas, C 2 H 4 Liquids 
Acetylene, C 2 H, 
Oil-gas, C 4 H; 



Toluole, CML 



Naphthaline, C 10 H 8 
Anthracene, C u H l0 
Paraffine, C. r H2. ff + 2 
I Coke, . G 



108 



COMPOSITION OF COAL-GAS. 



The nitrogen of the coal reappear 

Gases 



in the forms of — 



Nitrogen. 

Ammonia, . . NH 3 

( Aniline, . . C 6 H 7 1 

Liquids < Quinoline, . . C 9 H 7 1 

( Hydrocyanic acid, CHN. 



The oxygen contributes to the production of — 

Liquids 



Gases f Carbonic oxide, 
uases | Carbonic acid} 



CO 
CO, 



Sulphur is found among the products as 
Sulphuretted hydrogen gas, H 2 S 



Liquid 
(very volatile). 



Alkaline. 



Water, . H 2 

Acetic acid, C 2 tf 4 3 
Carbolic acid, C 6 H 6 



Bisulphide of carbon, CS 2 



The illuminating gas obtained from coal consists essentially of free hydro- 
gen, marsh-gas, olefiant gas, and carbonic oxide, with small quantities of 
acetylene, benzole vapour, and some other substances. 

A fair general idea of its composition is given by the following table .: — 

Gas from Cannel Coal. 



Hydrogen, ..... 


45 '847 volumes 


Marsh-gas, ... 


40-948 


Carbonic oxide, .... 


4-167 


Olefiant gas, . 


5-504 


Carbonic acid, .... 


1-950 


Nitrogen, 


1-445 


Oxygen, 


0-139 



100-0 

The only constituents which contribute directly to the illuminating 
value of the gas are the marsh gas, olefiant gas, and similar hydrocar- 
bons (acetylene, and benzole vapour). 

The most objectionable constituent is the sulphur present as sulphur- 
etted hydrogen and bisulphide of carbon, for this is converted by com- 
bustion into sulphuric acid, which seriously injures pictures, furniture, 
&c. The object of the manufacturer of coal-gas is to remove, as far as 
possible, everything from it, except the constituents mentioned as essential, 
and at the same time to obtain as large a volume of gas from a given 
weight of coal as is consistent with a good illuminating value. 

The mode of purifying the gas, and the general arrangements for its 
manufacture, will be described in a later part of the work. 




Fig. 124. — Destructive distillation of coal. 

The destructive distillation of coal may be exhibited with the arrangement repre- 
sented in fig. 124. The solid and liquid products (tar, ammoniacal liquor, &c. ) are 



QUARTZ — SAND — FLINT. 



109 



condensed in the globular receiver (A). The first bent tube contains, in one- 
limb (B), a piece of red litmus paper to detect ammonia ; and in the other (C) 
a piece of paper impregnated with acetate of lead, which will be blackened by 
the sulphuretted hydrogen. The second bent tube a 
(D) contains enough lime-water to fill the bend, 
which will be rendered milky by the carbonic acid. 
The gas is collected over water, in the jar E, 
which is furnished with a jet from which the gas may 
be burnt when forced out by depressing the jar in 
water. 

The presence of acetylene., in coal-gas may be 
shown by passing the gas from the supply-pipe (A, 
fig. 125), first through a bottle (B) containing a little 
ammonia, then through a bent tube (C), with enough 
water to fill the bend, and a piece of bright sheet 
copper immersed in the water in each limb. After 
a short time the bright red flakes of the acetyl ide of copper will be seen in the 
water. 




Fig. 125. 



SILICON. 

79. In many of its chemical relations to other bodies this element will 
he found to hear a great resemblance to carbon ; but whilst carbon is 
remarkable for the great variety of compound forms in which it is met 
with in nature, silicon is always found in combination with oxygen, as 
silicic acid, or silica (Si0 2 ), either alone or united with various metallic 
oxides, with which it forms silicates. 

Silica Si0 2 = 60 parts by weight. — The purest natural variety of silica 
is the transparent and colourless variety of quartz known as rock crystal, 
the most widely diffused ornament of the mineral world, often seen crys- 
tallised in beautiful six-sided prisms, terminated by six-sided pyramids 
(fig. 126), which are 
always easily distinguish- 
ed by their great hardness, 
scratching glass almost as 
readily as the diamond. 
Coloured of a delicate 
purple, probably by a little 

organic matter, these crys- Fig. 126.— Crystal of quartz, 

tals are known as ame- 




; and when of a brown colour, as Cairngorm stones or Scotch pebbles. 
Losing its transparency and crystalline structure, we meet with silica in 
the form of chalcedony and of earnelian, usually coloured, in the latter, 
with oxide of iron. 

Hardly any substance has so great a share in the lapidary's art as silica, 
for in addition to the above instances of its value for ornamental purposes 
we find it constituting agate, cafs eye, onyx, so much prized for cameos^ 
opal, and some other precious stones. In opal the silica is combined 
with water. 

Sand, of which the whiter varieties are nearly pure silica, appears to 
have been formed by the disintegration of siliceous rocks, and has generally 
a yellow or brown colour, due to the presence of oxide of iron. 

The resistance offered by silica to all impressions has become proverbial 
in the case of flint, which consists essentially of that substance coloured 
with some impurity. Flints are generally found in compact masses, distri- 
buted in regular beds throughout the chalk formation ; their hardness. 



110 SILICA RENDERED SOLUBLE. 

which even exceeds that of quartz, formerly rendered them useful for 
striking sparks with steel, by detaching small particles of the metal, which 
are so heated by the percussion as to continue to burn (see p. 27) in the 
air, and to inflame tinder or gunpowder upon which they are allowed to fall. 

The part taken by silica in natural operations appears to be chiefly a 
mechanical one, for which its stability under ordinary influences peculiarly 
fits it, for it is found to constitute the great bulk of the soil which serves 
as a support and food-reservoir of land-plants, and enters largely into the 
composition of the greater number of rocks. 

But that this substance is not altogether excluded from any share in 
life is shown by its presence in the shining outer sheath of the stems of 
the grasses and cereals, particularly in the hard external coating of the 
Dutch rush used for polishing ; and this alone would lead to the inference 
that silica could not be absolutely insoluble, since the capillary vessels of 
plants are known to be capable of absorbing only such substances as are in 
a state of solution. Many natural waters also present us with silica in a 
dissolved state, and often in considerable quantity, as, for example, in the 
Geysers of Iceland, which deposit a coating of silica upon the earth around 
their borders. 

Pure water, however, has no solvent action upon the natural varieties 
of silica. The action of an akali is required to bring it into a soluble form. 

To effect this upon the small scale, a few crystals of common washing- 
soda (carbonate of soda) may be powdered and dried ; a little of the dried 
powder is placed upon a piece of platinum foil slightly bent up (fig. 127), 




Fig. 127. — Fusion on platinum foil. 

and is fused by directing the flame of a blowpipe upon the under side of 
the foil. As soon as the carbonate of soda is perfectly liquefied, a small 
quantity of very finely powdered white sand is thrown into it, when brisk 
effervescence will be observed, and the particles of sand will dissolve ; 
fresh portions of sand may now be added as long as they produce effer- 
vescence, which is due to the escape of the carbonic acid, and since, in 
general, one acid can only be displaced by another, it is but reasonable to 
infer that the sand really possesses acid properties, and hence the fitness 
of its chemical name, silicic acid. 

The piece of platinum foil with the melted mass upon it may now be 
placed in a little warm water, and allowed to soak for some time, when it 
will gradually dissolve, forming a solution of silicate of soda. This solu- 
tion will be found decidedly alkaline to test-papers ; for silicic acid, like 
carbonic, is too feeble an acid to neutralise entirely the alkaline properties 
of the soda. 

If a portion of the solution of silicate of soda in water be poured into 
a test-tube, and two or three drops of hydrochloric acid added to it, with 



DIALYSED SILICA. Ill 

occasional agitation, effervescence will be produced by the expulsion of 
any carbonic acid still remaining, and the solution will be converted into 
a gelatinous mass by the separation of hydrated silicic acid. But if 
another portion of the solution of silicate of soda be poured into an excess 
of dilute hydrochloric acid (i.e., into enough to render the solution dis- 
tinctly acid), the silicic acid will remain dissolved in the water, together 
with the chloride of sodium formed by the action of the hydrochloric acid 
upon the soda. 

In order to separate the chloride of sodium from the silicic acid, the 
process of dialysis * must be resorted to. 

Dialysis is the separation of dissolved substances from each other by 
taking advantage of the different rates at which they pass through moist 
diaphragms or septa. 

If the mixed solution of chloride of sodium and silicic acid were poured 
upon an ordinary paper filter, it would pass through without alteration ; 
but if parchment paper be employed, which is not pervious to water, 
although readily moistened by it, none of the liquid will pass through. 
If the cone of parchment paper be supported upon a vessel filled with 
distilled water (fig. 128), so that the water may be in contact with the 
outer surface of the cone, the hydrochloric acid and the chloride of sodium 
will pass through the substance of the parchment paper, and the water 
charged with them may be seen descending in dense streams 
from the outside of the cone. After a few hours, especially 
if the water be changed occasionally, the whole of the 
hydrochloric acid and chloride of sodium will have passed 
through, and a pure solution of silicic acid in water will 
remain in the cone. 

This solution of silicic acid is very feebly acid to blue 
litmus paper, and not perceptibly sour to the taste. It 
has a great tendency to set into a jelly in consequence of 
the sudden separation of hydrated silicic acid. If it be 
slowly evaporated in a dish, it soon solidifies; but, by con- 
ducting the evaporation in a flask, so as to prevent any 
drying of the silicic acid at the edges of the liquid, it may 
be concentrated uutil it contains 14 per cent, of silicic acid. When this 
solution is kept, even in a stoppered or corked bottle, it sets into a trans- 
parent gelatinous mass, which gradually shrinks and separates from the 
water. When evaporated, in vacuo, over sulphuric acid, it gives a trans- 
parent lustrous glass which is composed of 22 per cent, of water and 78 per 
cent, of silicic acid (H 2 O.Si0 2 ). 

This hydrate of silica cannot be redissolved in water, and is only soluble 
to a slight extent in hydrochloric acid. If it be heated to expel the water, 
the anhydrous silicic acid which remains is insoluble both in water and in 
hydrochloric acid, but is dissolved when boiled with solution of potash or 
soda, or their carbonates. 

Silicic acid in the naturally crystallised form, as rock crystal and quartz, 
is insoluble in boiling solutions of the alkalies, and in all acids except 
hydrofluoric ; but amorphous silica (such as that found at Farnham) is 
readily dissolved by boiling alkalies. These represent, in fact, two dis- 
tinct modifications of silica. A transparent piece of rock crystal may be 
heated to bright redness without change, but if it be powdered previously 
to being heated, its specific gravity is diminished from 2*6 to 2 '4, and it 
* From SiaXvu), to part asunder. 




112 



ACID CHARACTER OF SILICA. 



becomes soluble in boiling alkalies, having been converted into the amor- 
phous modification. 

Crystals of quarts have been obtained artificially by the prolonged 
action of water upon glass at a high temperature under pressure. When 
fused with the oxyhydrogen blowpipe, silica does not crystallise, being 
thus converted into the amorphous variety of sp. gr. 2*3. 

To prepare the amorphous modification of silica artificially, white sand in very- 
fine powder may be fused, in a platinum crucible, with six times its weight of a mix- 
ture of equal weights of carbonate of potash and carbonate of soda, the mixture being 
more easily fusible than "either of the carbonates separately. The crucible may be 
heated over a gas-burner supplied with a mixture of gas and air, or may be placed in 
a little calcined magnesia contained in a fire-clay crucible, which may be covered up 
and introduced into a good fire. The platinum crucible is never heated in direct 
contact with fuel, since the metal would become brittle by combining with carbon, 
silicon, and sulphur derived from the fuel. The magnesia is used to protect the pla- 
tinum from contact with the clay crucible. When the action of the silicic acid upon 
the alkaline carbonates is completed, which will be indicated by the cessation of the 
effervescence, the platinum crucible is allowed to cool, placed in an evaporating dish, 
and soaked for a night in water, when the mass should be 
entirely dissolved. Hydrochloric acid is then added to 
the solution, with occasional stirring, until it is distinctly 
acid to litmus paper. On evaporating the solution, it will, 
at a certain point, solidify to a gelatinous mass of hydrated 
silicic acid, which would, be spirted out of the dish if 
evaporation over the flame were continued. To prevent 
this, the dish is placed over an empty iron saucepan (fig. 
129), so that the heat from the flame may be equally 
distributed over the bottom of the dish. When the mass 
is quite dry, the dish is allowed to cool, and some water 
is poured into it, which dissolves the chlorides of potas- 
sium and sodium (formed by the action of the hydro- 
chloric acid upon the silicates of potash and soda), and 
leaves the silicic acid in white flakes. These may be 
collected upon a filter (fig. 130), and washed several times with distilled water. 
The filter is then carefully spread out upon a hot iron plate, or upon a hot brick, and 

allowed to dry, when the silicic acid is 
left as a dazzling white powder, which 
must be strongly heated in a porcelain 
or platinum crucible to expel the last 
traces of water. It is remarkable for 
its extreme lightness, especially when 
heated, the slightest current of air easily 
blowing it away. 

80. For effecting such fusions as that 
just described, an air-gas blow-pipe (A, 
fig. 131) supplied with air from a double- 
action bellows (B), worked by a treadle (C), 
will be found most convenient. Where 
gas is not at hand, the fusion may be 
effected in a small furnace (fig. 132), sur- 
mounted with a conical chimney, and fed 
with charcoal. 

81. Silicates. — The acid proper- 
ties of silicic acid are so feeble that 
it is a matter of great difficulty to 
determine the proportion of any 
base which is required to unite with 
it in order to form a chemically 

it does not destroy the action of the 
alkalies upon test-papers, and we are, therefore, deprived of this method of 




Fig. 129. 




Fig. 130.— Washing a precipitate, 
neutral salt. Like carbonic acid. 



AMOKPHOUS SILICON. 



113 



ascertaining the proportion of alkali which neutralises it in a chemical sense. 
In attempting to ascertain the quantity of alkali with which it combines 
from that of the carbonic acid which it expels when heated with an 
alkaline carbonate, it is found that the proportion of carbonic acid 
expelled varies considerably, according to the temperature and the pro- 
portion of alkaline carbonate employed, probably because the attractions 
of silicic and carbonic acids for the alkaline bases are pretty evenly 
balanced. 

By heating silicic acid with hydrate of soda (Na 2 O.H 2 0), it is found 
that 60 parts of silicic acid expel 36 parts of water, however much hydrate 
of soda is employed, and the same proportion of water is expelled from 
hydrate of baryta (BaO.H 2 0) when heated with silicic acid. 

The formula Si0 2 represents 60 parts by weight of silicic acid, and 36 
parts represent two molecules of water which were combined in the 
hydrates with soda and baryta respectively. Hence it would appear that 
one molecule of silicic acid is disposed to combine with two molecules 
of an alkali, and since it is found that several of the crystallised mineral 
silicates contain a quantity of base equivalent to two molecules of an 
alkali combined with one molecule of silicic acid, it is usual to represent 
it as a tetrabasic acid, that is, an acid requiring two molecules of an 
alkali (containing four atoms of metal) to form a chemically neutral salt. 

The circumstance that silicic acid is not capable of being converted into 
vapour at a high temperature, 
enables it to expel from their 
combinations with bases many 
other acids which, at ordinary 
temperatures, are able to displace 
silicic acid. Thus, sulphuric acid 
has a far more powerful attrac- 
tion for bases than silicic acid, at 
the ordinary temperature, but 
when a mixture of silicic acid 
with a sulphate is strongly heated, 
the tendency of the sulphuric acid 
to assume the vaporous state at 
this temperature determines the 
decomposition of the sulphate and 
the formation of a silicate. 

The silicates form by far the 
greatest number of minerals. The 
different varieties of clay consist 
of silicate of alumina ; feldspar is Fi S- 13l.-Air-gas blowpipe table, 

a silicate of alumina and potash \ meerschaum is a silicate of magnesia. 

The different kinds of glass are composed of silicates of potash, soda, 
lime, oxide of lead, &c. 

None but the silicates of the alkalies are soluble in water. 

82. Silicon or Silicium (Si = 28 parts by weight). — From the remarkably 
unchangeable character of silica, it is not surprising that it was long re- 
garded as an elementary substance. In 1813, however, Davy succeeded in 
decomposing it by the action of potassium, and in obtaining an impure 
specimen of silicon. It has since been produced, far more easily, by con- 
verting the silicic acid into silico-nuoride of potassium (2KF.SiF 4 ), and 
decomposing this at a high temperature with potassium or sodium, which 

H 




114 



CHEMICAL RELATIONS OF SILICON. 




Fig. 132.— Charcoal furnace. 



combines with the fluorine to form a salt capable of being dissolved out by 
water, leaving the silicon in the form of a brown powder (amorphous silicon) 
which resists the action of all acids, except hydrofluoric, which it decomposes, 
forming fluoride of silicon and evolving hydrogen (Si + 4HF = SiF 4 + H 4 ). 
Tt is also dissolved by solution of hydrate of 
potash, with evolution of hydrogen, and for- 
mation of silicate of potash. It burns bril- 
liantly when heated in oxygen, but not com- 
pletely, for it becomes coated with silica 
which is fused by the intense heat of the 
combustion. When heated with the blow- 
pipe on platinum foil, it eats a hole through 
the metal, with which it forms the fusible 
silicide of platinum. 

If silico-fluoride of potassium be fused with 
aluminum, a portion of the latter combines 
with the fluorine, and the remainder com- 
bines with the silicon, forming a silicide of 
aluminum. By boiling this with hydro- 
chloric and hydrofluoric acids in succession, 
the aluminum is extracted, and crystalline scales of silicon, with a 
metallic lustre resembling black lead, are left (graphitoid silicon). In this 
form the silicon has a specific gravity of about 2*5, and refuses to burn 
in oxygen, or to dissolve in hydrofluoric acid. A mixture of nitric and 
hydrofluoric acids, however, is capable of dissolving it. Like graphite, 
this variety of silicon conducts electricity, though amorphous silicon is 
a non-conductor. The amorphous silicon becomes converted into this 
incombustible and insoluble form under the action of intense heat. It 
is worthy of remark that the combustibility of amorphous carbon 
(charcoal) is also very much diminished by exposure to a high tem- 
perature. 

Unlike carbon, however, silicon is capable of being fused at a tempera- 
ture somewhat above the melting point of cast iron; on cooling it forms 
a brilliant metallic-looking mass, which may be obtained, by certain 
processes, crystallised in octahedra so hard as to scratch glass like a 
diamond. 

In their chemical relations to other substances there is much resem- 
blance between silicon and carbon. They both form feeble acids with 
oxygen, which correspond in composition. Silicon, however, is capable 
of displacing carbon from carbonic acid, for if carbonate of potash be • 
fused with silicon, the latter is dissolved, forming silicate of potash, and 
carbon is separated. Silicon also resembles carbon in its disposition to 
unite with certain metals to form compounds which still retain their 
metallic appearance. Thus silicon is found together with carbon in cast 
iron, and it unites directly with aluminum, zinc, and platinum, to form 
compounds resembling metallic alloys. Nitrogen enters into direct union 
with silicon at a high temperature, though it refuses to unite with carbon 
except in the presence of alkalies. In their relation to hydrogen, these 
two elements are widely different, for silicon is only known to form one 
compound with hydrogen, and that of a very unstable character. 

The hydride of silicon has been found to have a composition corre- 
sponding with the formula SiH 4 . It derives its interest chiefly from the 
property of taking fire spontaneously in contact with the air, in which it 



HYDRIDE OF SILICON. 115 

burns with a brilliant white flame, giving off clouds of silica, and deposit- 
ing a brown film of silicon upon a cold surface. 

Hydride of silicon is prepared by decomposing silicide of magnesium with dilute 
hydrochloric acid. The silicide of magnesium is obtained by fusing chloride of mag- 
nesium (MgCl 2 ) with silico-fluoride of sodium (21sraF . SiF 4 ), and metallic sodium, 
when the latter combines with the chlorine and fluorine, leaving the magnesium free 
to unite with the silicon. 

The chloride of magnesium may be prepared by dissolving ordinary carbonate of 
magnesia in hydrochloric acid, adding three paits of chloride of ammonium for each 
part of carbonate of magnesia, evaporating to dryness in a porcelain dish, fusing the 
residue, and pouring it out on to a clean stone. Being very deliquescent, it must be 
kept in a well-closed bottle. 

Silico-fluoride of sodium is made by neutralising hydro-fluosilicic acid with car- 
bonate of soda, and evaporating to dryness. 

To increase the fusibility of the mixture, some fused common salt will be re- 
quired. Dried salt maybe melted in a fire -clay crucible, at a bright red heat, and 
poured out upon a clean dry stone. 

Forty parts of the chloride of magnesium, 35 of silico-fluoride of sodium, 10 of 
fused chloride of sodium, and 20 of sodium in slices, are rapidly weighed, shaken 
together in a dry bottle, and thrown into a red-hot clay crucible, which is then 
covered and heated as long as the yellow flame of sodium vapour is perceptible. 
After cooling, the crucible is broken, when a dark-coloured layer of silicide of mag- 
nesium will be found beneath a white layer of chloride and fluoride of sodium. 
The silicide of magnesium must be rapidly detached, and preserved in a well- 
stopped bottle. 

The silicide of magnesium is coarsely powdered, and introduced into a Woulfe's 
bottle (fig. 133) provided with a funnel tube, and a short wide tube for delivering 
the gas. The bottle is filled up with water (previously 
boiled to expel air, and allowed to cool), and. placed in 
the pneumatic trough (containing boiled water), so 
that both bottle and tubes may remain filled with 
water. A gas-jar, filled with boiled water, having 
been placed over the delivery-tube, some strong hydro- 
chloric acid is added through the funnel, great care 
being taken that no air shall enter. The hydride of 
silicon is at once evolved, and must be allowed to 
stand over water for some little time, to allow the 
froth, caused by a slight separation of silica, to sub- 
side. The gas may then be transferred to a capped 
jar, with a stop- cock, from which it may be allowed to 
pass into the air for the examination of its flame. 

When cast iron, containing silicon, is boiled with jij„ ^33 

hydrochloric acid until the whole of the iron is dis~- 

solved, a grey frothy residue is left. If this be collected on a filter, well washed 
and dried, it is found to consist of black scales of graphite, mixed with a very light 
white powder. On boiling it with potash, hydrogen is evolved, and the white 
powder dissolves, forming a solution containing silicate of potash. This white 
powder appears to be identical with a substance obtained by other processes, and 
called leucone* which is believed to have the composition Si 3 H 4 5 , and has been 
regarded as a hydride of protoxide of silicon, 3SiO . 2H 2 0. Its action upon solution 
of potash would be explained by the equation 

Si 3 H 4 5 + 12KHO = 3(2K 2 O.Si0 2 ) + H 6 + 5H 2 . 

Leucone is slowly converted into silicic acid, even by the action of water, hydrogen 
being disengaged. 

Another compound, containing silicon, hydrogen, and oxygen, has been named 
silicone. It is a yellow substance, the general characters of which resemble those of 
the compound last described. When exposed, under water, to the action of sun- 
light, hydrogen is evolved, and the yellow body becomes converted into leucone. 

The atomic weight of silicon is generally represented by the number 

* Aei/Kos, white. 




116 



BORON. 



28, though here, as in the case of carbon, theoretical considerations are 
relied upon, since the specific gravity of vapour of silicon cannot he ascer- 
tained by experiment, and no assistance is afforded by the specific heat. 



BORON. 

83. Closely allied to silicon is another element, boron, which has at 
present never been found in animal or vegetable bodies, but appears to 
be entirely confined to the mineral kingdom. 

Boracic acid (B 2 3 = 69'8 parts by weight). — A saline substance called 
borax (Na 2 0.2B 2 3 , lOAq.), has long been used in medicine, in working 
metals, and in making imitations of precious stones ; this substance was 
originally imported from India and Thibet, where it was obtained in 
crystals from the waters of certain lakes, and came into this country 
under the native designation of tincal, consisting of impure borax, sur- 
rounded with a peculiar soapy substance, which the refiner of borax 
makes it his business to remove. 

In 1702, in the course of one of those tentative experiments to which, 
though empirical in their nature, scientific chemistry is now so deeply 
indebted, Homberg happened to distil a mixture of borax and green 
vitriol (sulphate of iron), when he obtained a new substance in pearly 
plates, which was found useful in medicine, and received the name of 
sedative salt. A quarter of a century later, Lemery found that this sub- 
stance might be separated from borax by employing sulphuric acid instead 
of sulphate of iron ; but another quarter of a century elapsed before it 
was shown that in borax these pearly crystalline scales were combined 
with soda, and were possessed of acid properties which entitle them to 
receive the name boracic acid. 

Much more recently this acid has been obtained in a free state from 
natural sources, and is now largely imported into this country from the 
volcanic districts in the north of Italy, where it issues from the earth in 




Fig. 134. — Boracic lagune and evaporating pans. 

the form of vapour, accompanied by violent jets of steam, which are 
known in the neighbourhood as soffioni. It would appear easy enough, 
by adopting arrangements for the condensation of this steam, to obtain 
the boracic acid which accompanies it, but it is found necessary to cause 
the steam to deposit its boracic acid by passing it through water, for 
which purpose basins of brickwork (lagunes, fig. 1 34) are built up around 



BOEACIC ACID. 117 

the soffioni, and are kept filled with water from the neighbouring springs 
or brooks ; this water is allowed to flow successively into the different 
lagunes, which are built upon a declivity for that purpose, and it thus 
becomes impregnated with about 1 per cent, of boracic acid. The neces- 
sity for expelling a large proportion of this water, in order to obtain the 
boracic acid in crystals, formed for a long time a great obstacle to the 
success of this branch of industry in a country where fuel is very expen- 
sive. In 1817, however, Larderello conceived the project of evaporating 
this water by the steam-heat afforded by the soffioni themselves, and 
several hundred tons of boracic acid are now annually produced in this 
manner. The evaporation is conducted in shallow leaden evaporating 
pans (A, fig. 134), under which the steam from the soffioni is conducted 
through the flues (F) constructed for that purpose. As the demand for 
boracic acid increased on account of the immense consumption of borax 
in the porcelain manufacture, the experiment was made, with success, of 
boring into the volcanic strata, and thus producing artificial soffioni, yield- 
ing boracic acid. 

The crystals of boracic acid, as imported from these sources, contain 
salts of ammonia and other impurities. They dissolve in about three 
times their weight of boiling water, and crystallise out on cooling, since 
they require 26 parts of cold water to dissolve them. These crystals are 
represented by the formula 3H 2 O.B 2 3 . If they are sharply heated in a 
retort, they partly distil over unchanged, together with the water derived 
from the decomposition of another part ; but if they be heated to 212° F. 
only, they effloresce, and become converted into H 2 O.B 2 3 . When this 
is further heated, the whole of the water passes off, carrying with it a 
little boracic acid, and the acid fuses to a glass, which remains perfectly 
transparent on cooling (vitreous boracic acid). This anhydrous boracic 
acid is slowly volatilised by the continued action of a very high tempera- 
ture. It dissolves very slowly in water. 

A characteristic property of boracic acid is that of imparting a green 
colour to flames. Its presence may thus be detected in the steam issuing 
from a boiling solution of boracic acid in water, for if a spirit-lamp flame, 
or a piece of burning paper, be held in the steam, the flame will acquire 
a green tint, especially at the edges. 

The colour is more distinctly seen when the crystallised boracic acid is heated 
on platinum foil in a spirit-flame or an air-gas flame; and still better when the 
crystals are dissolved in boiling alcohol, and the solution burnt on a plate. The 
presence of boracic acid in borax may be ascertained by mixing the solution of borax 
with strong sulphuric acid to liberate the boracic acid, and adding enough alcohol to 
make the mixture burn. Another peculiar property of boracic acid is its action 
upon turmeric. If a piece of turmeric paper be dipped in solution of boracic acid, 
and dried at a gentle heat, it assumes a fine brown-red colour, which is changed 
to green or blue by potash or its carbonate. In applying this test to borax, the 
solution is slightly acidified with hydrochloric acid, to set free the boracic acid, before 
dipping the paper. 

Borates. — Boracic acid, like silicic, must be classed among the feeble 
acids. It colours litmus violet only, like carbonic acid, and does not 
neutralise the action of the alkalies upon test-papers. At high tempera- 
tures fused boracic acid dissolves the metallic oxides to form transparent 
glassy borates, which have, in many cases, very brilliant colours, and upon 
this property depend the chief uses of boracic acid in the arts. 

Unlike the silicates, the borates are comparatively rare in the mineral 
world. No very familiar mineral substance contains boracic acid. . A 



118 DIAMOND OF BORON. 

double borate of soda and lime, called boro-natrocalcite (Na 2 0.2B 2 3 , 
2(Ca0.2B 2 3 ), 18H 2 0), is imported from Peru for the manufacture of 
borax ; and the mineral known as boracite is a borate of magnesia. 

In determining the proportion of base which boracic acid requires to 
form with it a chemically neutral salt, the same difficulties are met with 
as in the case of silicic acid (p. 112) ; out since it is found that 69*8 parts 
of boracic acid (the weight represented by B 2 3 ) displace 54 parts of water 
(three molecules) from hydrate of soda and from hydrate of baryta, both 
employed in excess, it would appear that the boracic acid requires three 
molecules of an alkali fully to satisfy its acid character. 

84. Boron. — B = 10"9 parts by weight. — It was in the year 1808 that 
Gay-Lussac and Thenard succeeded, by fusing anhydrous boracic acid 
with potassium, in extracting from it the element boron as an olive-green 
powder (amorphous boron), which has a general resemblance to silicon, 
but, unlike that element, may be oxidised by nitric acid. It also requires 
a higher temperature to fuse it than is required by silicon. The brilliant 
copper-coloured scales obtained by a process similar to that which fur- 
nishes the graphitoid silicon, and formerly regarded as graphitoid boron, 
consist really of a compound of boron with aluminum (A1B 2 ). 

The most remarkable form of boron is the crystallised variety or diamond 
of boron, which is obtained by very strongly heating amorphous boron 
with aluminum, and afterwards extracting the aluminum from the mass 
with hydrochloric acid. These crystals are brilliant transparent octahedra, 
which are sometimes nearly colourless, and resemble the diamond in their 
power of refracting light, and in their hardness, which is so great that 
they will scratch rubies, and will even wear away the surface of the 
diamond.' 54 ' This form of boron cannot be attacked by any acid, but is 
dissolved by fused hydrates of the alkalies. The flame of the oxyhydrogen 
blowpipe does not fuse it, and it only undergoes superficial conversion 
into boracic acid when heated to whiteness in oxygen. When heated to 
redness in chlorine, however, it burns, forming chloride of boron. Boron 
closely resembles silicon in its chemical relations to the other elements. 
It is not known, however, to form a compound with hydrogen, and has a 
greater disposition to combine with nitrogen than is manifested by silicon. 
It absorbs nitrogen readily when heated to redness, forming a white 
infusible insoluble powder,' the nitride of boron (BIN"). 

85. The elements carbon, boron, and silicon form a natural group, pos- 
sessing many properties in common. They are all capable of existing in 
the amorphous, the graphitoid, and the crystalline forms ; all incapable of 
being converted into vapour ; all exhibit a want of disposition to dissolve ; 
all form feeble acids with oxygen by direct union ; and all unite with 
several of the metals to form compounds which resemble each other. 
Boron and silicon are capable of direct union with nitrogen, and so is 
carbon if an alkali be present. Recent researches attribute to silicon the 
power of occupying the place of carbon in some organic compounds, and 
the formulae of leucone and silicone (Si 3 H 4 5 and Si 6 H 6 4 ) strongly remind 
us of the organic compounds of carbon with hydrogen and oxygen. In 
many of its physical and chemical characters, silicon is closely allied with 
the metals, and it will be found that tin and titanium bear a particular 
resemblance to it in their chemical relations. 

* The author has known them to cut through the bottom of the beaker-glass used in 
separating them from the aluminum. 



NITROGEN — AMMONIA. 



119 



NITROGEK 

N = 14 parts by weight = 1 vol. 14 grns. =467 cub. in. at 60° F. and 30" Bar. 
14 grms. = ll'2 litres at 0° C. and 760 mm. Ear. 

86. This element, which has already been referred to as forming four- 
fifths of the volume of air, is elsewhere found in nature in the forms of 
saltpetre or nitrate of potash (KN0 3 ), and Chili saltpetre or nitrate of 
soda (Na]ST0 3 ). It also occurs as ammonia (NH 3 ) in the atmosphere and 
in the gaseous emanations from volcanoes. It is contained in the greater 
number of animal, and in many vegetable substances, and therefore has a 
most important share in the chemical phenomena of life. 

Nitrogen is generally obtained by burning phosphorus in a portion of 
air confined over water (fig. 135). The phosphorus is floated on the water 
in a small porcelain dish, kindled, and 
covered with a bell-jar. The nitrogen 
remains mixed with clouds of phosphoric 
acid (P 2 5 ), which may be removed by 
allowing the gas to stand over water. 

When nitrogen is required in larger 
quantity, it is more conveniently prepared 
by passing air from a gas-holder over 
metallic copper heated to redness in a tube. 
The negative properties of this gas, how- 
ever, are so very uninteresting, and render 
it so useless for most chemical purposes, 
that it will be unnecessary to give further 
details respecting its preparation. The 
remarkable chemical inactivity of free nitrogen has been alluded to in the 
article on atmospheric air. It has been seen, however, to be capable of 
combining directly with boron and silicon, and magnesium and titanium 
unite with it even more readily at a high temperature. It is conspicuous 
among the elements for forming, with hydrogen, a powerful alkali (am- 
monia, NH 3 ), and with oxygen a powerful acid (nitric acid, N 2 5 ), whilst 
the feeble chemical ties which hold it in combination with other elements, 
joined to its character of a permanent gas, render many of its compounds 
very unstable and explosive, as is the case with the so-called chloride and 
iodide of nitrogen, gun-cotton, the fulminates of silver and mercury, nitro- 
glycerine, &c. 

The discovery of nitrogen was made by Eutherford (Professor of Botany 
in the University of Edinburgh) in 1772, who was led to it by the obser- 
vation that respired air was still unfit to support life when all the carbonic 
acid had been absorbed from it by a caustic alkali. Hence the name azote 
(a priv. and £(d?) life) formerly bestowed upon this gas. 




Preparation oi nitrogen. 



Ammonia. 

NH 3 - 17 parts by weight == 2 vols. 

87. The proportion of ammonia existing in atmospheric air is so small 
that it is difficult to determine it with precision ; it appears, however, not 
to exceed one-hundredth of a grain in a cubic foot. This scarcity of 



120 



PREPARATION OF AMMONIA. 



ammonia in air is not to be accounted for by a scantiness in the supply, 
but rather by an excess in the demand; since ammonia is constantly sent 
forth into the air by the putrefaction of animal and vegetable substances 
containing nitrogen. Plants do not appear to be capable of absorbing 
from the atmosphere the nitrogen which it contains so abundantly in the 
uncombined form, but to derive their chief supply of that element from 
the ammonia, brought down by raiu from the atmosphere, into which it is 
continually introduced from various sources. During the life of an 
animal, it restores to the air the nitrogen which formed part of its wasted 
organs, in part directly as ammonia in the breath and in the exhalation 
from the skin,* whilst another portion is separated as urea and uric acid 
in the urine, to be eventually converted into ammonia when the excretion 
undergoes putrefaction. Dead animal and vegetable matter when putre- 
fying, restores its nitrogen to the air, chiefly in the forms of ammonia 
and substances closely allied to it, but partly also, it is said, in the free 
state. 

The liquor ammonia*, or solution of ammonia in water, which is so largely 
used in medicine and the arts, is obtained chiefly from the ammoniacal 
liquor resulting from the destructive distillation of coal for the manufac- 
ture of gas. The ammoniacal liquor of the gas-works contains ammonia 
in combination with carbonic and hydrosulphuric acid. As the first step 
towards extracting the ammonia in a pure state, the liquor is neutralised 
with hydrochloric acid, which combines with the ammonia, expelling the 
carbonic and hydrosulphuric acid gases. Since the latter has a very bad 
sin ell and is injurious to health, the neutralisation is generally effected 
in covered vats furnished with pipes, which convey the gases into a furnace 
where the hydrosulphuric acid is burnt, forming water and sulphurous 
acid. The solution of hydrochlorate of ammonia is evaporated to expel 
part of the water, and allowed to cool in wooden vessels lined with lead, 
where the hydrochlorate is deposited in. crystals which contain a good 
deal of tarry matter. These crystals are moderately heated in an iron pan 
to deprive them of tar, and are finally purified by sublimation, that is, by 
converting them into vapour, and allowing this vapour to condense again 
into the solid form. For this purpose the crys- 
tals are heated in a cylindrical iron vessel covered 
with an iron dome lined with fire-clay. The hydro- 
chlorate of ammonia rises in vapour below a red 
heat, and condenses upon the dome in the form of 
the fibrous cake known in commerce as sal-am- 
moniac. 

To obtain ammonia from this salt, an ounce of 
it is reduced to coarse powder, and rapidly mixed 
with two ounces of powdered quicklime. The 
mixture is gently heated in a dry Florence flask 
(fig. 136), and the gas, being little more than half 
as heavy as air (sp. gr. 0'59), may be collected 
in dry bottles by displacement of air, the bottles 
being allowed to rest upon a piece of tin plate 
which is perforated for the passage of the tube. 
To ascertain when the bottles are filled, a piece of 
red litmus paper may be held at some little distance above the mouth, 

* Some doubt exists as to the exhalation of ammonia from the lungs and skin of man 
under normal conditions. 




Fig. 136. — Preparation 
of ammonia. 



PROPERTIES OF AMMONIA. 



121 



when it will at once acquire a bine colour if the ammonia escapes. The 
bottles should be closed with greased stoppers. 

The action of the lime upon hydrochlorate of ammonia is explained by 
the following equation : — 



2(NH 3 .HC1) 

Hydrochlor. amm. 



CaO = CaCl 2 + H 2 

Lime. Chloride of calcium. 



2NH 3 

Ammonia. 



The readiest method of obtaining gaseous ammonia for the study of its propor- 
ties consists in gently heating the 
strongest liquor ammonioe in a retort 
or flask provided with a bent tube for 
collecting the gas by displacement (fig. 
137). The gas is evolved from the 
solution at a very low heat, and may 
be collected unaccompanied by steam. 

Ammonia is readily distin- 
guished by its very characteristic 
smell, and its powerful alkaline 
action upon red litmus and tur- 
meric papers. It is absorbed by 
water in greater proportion by 
volume than any other gas, one 
volume of water absorbing more 
than 700 volumes of ammonia 
at the ordinary temperature, and 
becoming one-and-a-half volumes 
gravity 0'88. 




Fig. 137. 



of solution of ammonia of specific 
No chemical combination appears to take place between 
the water and ammonia, for the gas gradually escapes on exposing the 
solution to the air, and no definite compound of the two has been noticed. 
Moreover, the quantity of ammonia retained by the water is dependent 
upon the temperature and pressure, as would be expected if the ammonia 
were merely dissolved and not combined with the water. The escape of 
the gas from the solution is attended with great production of cold, much 
heat becoming latent in the conversion of the ammonia from the liquid to 
the gaseous state. 

The rapid absorption of ammonia by water is well shown by filling a globular 
flask (fig. 138) with the gas, placing it with its mouth downwards in a small capsule 
of mercury which is placed in a large basin. If this 
basin be filled with water, it cannot come into contact 
with the ammonia until the mouth of the flask is 
raised out of the mercury, when the water will quickly 
enter and fill the flask. The water should be coloured 
with reddened litmus to exhibit the alkaline reaction 
of the ammonia. 

That the amount of ammonia in solution varies with 
the pressure, may be proved by filling a barometer tube, 
over 30 inches long, with mercury to within an inch 
of the top, filling it up with strong ammonia, closing 
the mouth of the tube, and inverting it with its mouth 
under mercury ; on removing the finger, the diminished 
pressure caused by the gravitation of the column of 
mercury in the tube will cause the solution of ammonia 
to boil, from the escape of a large quantity of the gas, l %' 

which will rapidly depress the mercury. If the pressure be now increased by gradu- 
ally depressing the tube in a tall cylinder of mercury (fig. 139), the water will again 
absorb the ammoniacal gas. 




122 



SPECIFIC GRAVITY OF LIQUIDS DETERMINED. 



To exhibit the easy expulsion of the ammoniacal gas from water by heat, 
a moderately thick glass tube, about 12 inches long and 
half an inch in diameter, may be nearly filled with mer- 
cury, and then filled up with strong solution of ammonia ; 
on closing it with the thumb and inverting it into a vessel of 
mercury (fig. 140) the solution will, of course, rise above the 
mercury to the closed end of the tube. By grasping this end 
of the tube in the hand, a considerable quantity of gas may be 
expelled, and the mercury will be depressed. If a little hot 
water be poured over the top of the tube, the latter will become 
filled with ammoniacal gas, which will be absorbed again by 
the water when the tube is allowed to cool, the mercury re- 
turning to fill the tube. 

The solution of ammonia, which, is an article of 
commerce, is prepared by conducting the gas into 
water contained in a two-necked bottle, the second 
neck being connected with a tube passing into another 
bottle containing water, in which any escaping am- 
monia may be condensed. The strength of the solu- 
tion is inferred from its specific gravity, which is 
lower in proportion as the quantity of ammonia in the 
solution is greater. 

Thus, at 57° F., a solution of sp. gr. 0*8844 contains 36 
parts by weight of ammonia in 100 parts of solution ; the sp. 
gr. 0-8976 indicates 30 per cent. ; 0*9106, 25 percent. ; 0*9251, 
20 per cent. ; 0*9414, 15 per cent. ; 0*9593, 10 per cent. ; 
0*979, 5 per cent. The specific gravity is ascertained by com- 
paring the weights of equal volumes of water and of the solu- 
tion at the same temperature. For this purpose, a light 
stoppered bottle is provided, capable of containing about two 
fluid ounces. This is thoroughly dried, and counterpoised in 
a balance by placing in the opposite pan a piece of lead, which 
may be cut down to the proper weight. The bottle is then filled with solution of 
ammonia, the temperature observed with a thermometer and recorded, the stopper 
inserted, and the bottle weighed. It is then well rinsed out, filled with distilled 

water, the temperature equalised 
with that of the ammonia by 
placing the bottle either in warm 
or cold water, and the weight as- 
certained as before. The specific 
gravity is obtained by dividing the 
weight of the solution of ammonia 
by that of the water. The ammonia- 
meter (fig. 141) is a convenient in- 
strument for rapidly ascertaining 
the specific gravity of liquids lighter 
than water. It consists of a hollow 
glass float with a long stem, 
weighted with a bulb containing 
shot or mercury, so that when placed 
in distilled water it may sink to 
1000° of the scale marked on the 
stem, this number representing 
the specific gravity of water. 
When placed in a liquid lighter 
than water, it must, of course, 
sink lower in order to displace 
more liquid (since solids sink 
until they have displaced their 
own weight of liquid). By trying 
it in liquids of known specific gravities, the mark upon the scale to which it sinks 
may be made to indicate the specific gravity of the liquid. The ammonia-meter 




Fig. 139. 




LIQUEFACTION OF AMMONIA. 



123 



generally has a scale so divided that it indicates at once the percentage weight of 
ammonia. In this country the specific gravity of a liquid is always supposed to be 
taken at 62° F. 

The common name for solution of ammonia, spirit of hart's liorn, is 
derived from the circumstance that it was originally obtained for medici- 
nal purposes by distilling shavings of that material. 

When ammonia is exposed to a temperature of - 40° F. (i.e., 72° 
below the freezing-point), or to a pressure of 6 J atmospheres at 50°, it 
condenses to a clear liquid, which solidifies at a tempera- 
ture of — 103° F. to a white crystalline mass. The com- 
parative ease with which it may be liquefied has led to its 
application in Carre's freezing apparatus (fig. 142), in which 
the gas generated by heating a concentrated solution of 
ammonia in a strong iron boiler (A) is liquefied by its own 
pressure in an iron receiver (B) placed in cold water. 
When the boiler is taken off the fire and cooled in water, 
the liquefied ammonia evaporates very rapidly from the 
receiver back into the boiler, thereby producing so much 
cold that a vessel of water placed in a cavity (C) in the re- 
ceiver is at once congealed into ice. A refrigerator con- 
structed upon this principle is employed in the salt gardens 
of the south of France, in order to render their crystal- 
lising operations independent of the temperature of the air. 

The liquefaction of ammonia is very easily effected by heating the ammoniated 
chloride of silver in one limb of a sealed tube, the other limb of which is cooled in a 
freezing mixture. A piece of stout light green glass tube (A, fig. 143), about 12 



Fig. 141. 




Fig. 142. — Carre's freezing apparatus. Fig. 143. 

inches long and half an ic : i in diameter, is drawn out at about an inch from one 
end to a narrow neck. Aliout 300 grains of chloride of silver (dried at 400° F.) are 
introduce I into the tube, so as to lie loosely in it. For this purpose a gutter of stiff 
paper (B) should be cut so as to slide loosely in the tube, the chloride of silver 
placed upon it, and when it has been thrust into the tube (held horizontally) the 
latter should be turned upon its axis, so that the chloride of silver may fall out of 
the paper, which may then be withdrawn. The tube is now drawn out to a narrow 
neck at about an inch from the other end, as in C, and afterwards carefully bent, as 
in D, care being taken that none of the chloride of silver falls into the short limb of 
the tube, which should be about four inches long. The tube is then supported by 
a holder, so that the long limb may be horizontal, and is connected, by a tube and 
cork, with an apparatus delivering dry ammonia, prepared by heating 1000 grains of 
sal-ammoniac with an equal weight of quick-lime in a flask, and passing the gas, 
first into an empty bottle (A, fig. 144) standing in cold water, and afterwards 
through a bottle (B) filled with lumps of quick-lime to absorb all aqueous vapour. 



124 



COMBUSTION OF AMMONIA IN OXYGEN. 



The long limb of the tube must be surrounded with filtering paper, which is kept 
wet with cold water. The current of ammonia should be continued at a moderate 





Fig. 144. 

rate, until the tube and its contents no longer increase in weight, which will occupy- 
about three hours — about 35 grains of ammonia being absorbed. The longer limb 
is sealed by the blowpipe flame whilst the gas is still passing, and then, as quickly 
as possible, the shorter limb, keeping that part of the tube which is occupied by the 
ammoniated chloride of silver still carefully surrounded by wet paper. 

"When the shorter limb of this tube (fig. 145) 
is cooled in a mixture of ice and salt (or of 8 
ounces of sulphate of soda and 4 measured ounces 
of common hydrochloric acid), whilst the longer 
limb is gently heated from end to end by waving 
a spirit flame beneath it, the ammonia evolved 
by the heat from the ammoniated chloride of 
silver, which partly fuses, will condense into a 
beautifully clear liquid in the cold limb. When 
this is withdrawn from the freezing mixture, and 
Fig, 145. -Liquefaction of ammonia. tne tube allowed to cool, the liquid ammonia will 

boil and gradually disappear entirely, the gas being 
again absorbed by the chloride of silver, so that the tube is ready to be used again. 

Ammonia is feebly combustible in atmospheric air, as may be seen by 
holding a taper jnst within the mouth of an inverted bottle of the gas, 
which burns with a peculiar livid flickering light around the flame, but 
will not continue to burn when the flame is removed. During its com- 
bustion the hydrogen is converted into water, and the nitrogen set free. 
In oxygen, however, ammonia burns with a continuous flame. 

This is very well shown by surrounding a tube delivering a stream of ammonia 

(obtained by heating strong solution 
of ammonia in a retort) with a much 
wider tube open at both ends (fig. 146),' 
through which oxygen is passed by 
holding a flexible tube from a gas-bag 
or gas - holder underneath it. On 
kindling the stream of ammonia it will 
give a steady flame of ten or twelve 
inches long. 

A similar experiment may be made 
with a smaller supply of oxygen, by 
lowering the tube delivering ammonia 
into a bottle or jar of oxygen, and 
applying a light to it just as it enters 
the mouth of the jar (fig. 147). 

The elements of ammonia are 

easily separated from each other 

Fi 146 by passing the gas through a red- 




AMMONIUM THEORY. 



125 



hot tube, or still more readily by exposing it to the action of the high 
temperature of the electric spark, when the volume of the gas rapidly bi- 
ll 





Fig. 147. 



Fig. 148. 



creases until it is exactly doubled, two volumes of ammonia being decom- 
posed into 1 volume of nitrogen and 3 volumes of hydrogen. 

For this experiment a measured volume of ammonia gas is confined over 
mercury (fig. 148), in a tube through which platinum wires are sealed for the 
passage of the spark from an induction-coil. The volume of the gas is doubled in 
a few minutes, and if the tube be furnished with a stop-cock (A), the presence of 
free hydrogen may be shown by filling the open limb with mercury and kindling the 
gas as it issues from the jet.* 

As might be expected from its powerfully alkaline character, ammonia 
exhibits a strong attraction for acids, which it 
neutralises perfectly. If a bottle of ammonia 
gas, closed with a glass plate, be inverted over 
a similar bottle of hydrochloric acid gas, and 
the glass plates withdrawn (fig. 149), the gases- 
will combine, with disengagement of much 
heat, forming a white solid, the hydrochlorate 
of ammonia (NH 3 .HC1), in which the acid and 
alkali have neutralised each other. Again, if 
ammonia be added to diluted sulphuric acid, the 
latterwill be entirely neutralised, and by evapo- 
rating the solution, crystals of the sulphate of 
ammonia (2NH 3 .H 2 O.S0 3 ) may be obtained. 

The substances thus produced by neutralising the acids with solution 
of ammonia bear a strong resemblance to the salts formed by neutralising 
the same acids with solutions of potash and soda, a circumstance which 
would encourage the idea that the solution of ammonia must contain an 
alkaline oxide similar to potash or soda. 

Berzelius was the first to make an experiment which appeared strongly 

* The eudiometer for passing electric sparks in rapid succession must have the platinum 
wires passed through the glass as shown in fig. 148, or it will be cracked by the heat of the 
sparks. The outlet tube B, closed by a small screw clamp C, pinching a caoutchouc connec- 
tor, allows the mercury to be drawn off when necessary, to equalise the level in the two limbs. 




Fig. 149. 



126 AMALGAM OF AMMONIUM. 

to favour this view (commonly spoken of as the ammonium theory of 
Berzelius). The negative pole of a galvanic battery was placed in contact 
with mercury at the bottom of a vessel containing a strong solution of 
ammonia, in which the positive pole of the battery was immersed. Oxygen 
was disengaged at this pole, whilst the mercury in contact with the 
negative pole swelled to four or five times its original bulk, and became 
a soft solid mass, still preserving, however, its metallic appearance. 
So far, the result of the experiment resembles that obtained when 
hydrate of potash is decomposed under similar circumstances, the oxygen 
separating at the positive pole, and the potassium at the negative, 
where it combines with the mercury. Beyond this, however, the 
analogy does not hold ; for in the latter case the metallic potassium can 
be readily separated from the mercury, whilst in the former, all attempts 
to isolate the ammonium have failed, for the soft solid mass resolves 
itself, almost immediately after its preparation, into mercury, ammonia 
(NHJ, and hydrogen, one atom of the latter being separated for each 
molecule of ammonia. This would also tend to support the conclusion, 
that a substance having the composition NH 3 + H or NH 4 had united 
with the mercury ; and since the latter is not known to unite with any non- 
metallic substance without losing its metallic appearance, it w T ould be fair to 
conclude that the soft solid was really an amalgam of ammonium. How- 
ever, the increase in the weight of the mercury is so slight, and the 
" amalgam," whether obtained by this or by other methods, is so unstable, 
that it would appear safer to attribute the swelling of the mercury to a 
physical change caused by the presence of the ammonia and hydrogen 
gases. It is difficult to believe that the solution of ammonia does really 
contain an oxide of ammonium (2NH 3 + H 2 = (NH 4 ) 2 0), when we find it 
evolving ammonia so easily ; but it is equally difficult, upon any other 
hypothesis, to explain the close resemblance between the salts obtained by 
neutralising acids with this solution, and those furnished by potash and soda. 

The ordinary mode of exhibiting the production of the so-called amalgam of ammo- 
nium consists in acting upon the hydrochlorate of ammonia (NH 3 .HC1), or chloride 
of ammonium (NH 4 C1), with the amalgam of sodium. A little pure mercury is 
heated in a test-tube, and a pellet of sodium thrown into it, when combination 
takes place with great energy. When the amalgam is nearly cool it may be 
poured into a larger tube containing a moderately strong solution of chloride 
of ammonium ; the amalgam at once swells to many times its former bulk, 
forming a soft solid substance lighter than water, which may be shaken out of 
the tube as a cylindrical mass, decomposing rapidly with effervescence, evolving am- 
monia and hydrogen, and soon recovering its original volume and liquid condition. 

88. Atomic weight and volume of nitrogen. — 17 grains of ammonia 
have been proved to contain 14 grains of nitrogen combined with 3 
grains of hydrogen. The latter gas being taken as the unit of atomic 
weight, the 3 grains would represent 3 atomic weights of hydrogen, and 
the question arises, How many atomic weights of nitrogen are represented 
by the 1 4 grains 1 On referring to the composition of ammonia by 
volume, we find that it furnishes three volumes of hydrogen for one volume 
of nitrogen when decomposed by the electric spark (p. 125), and hence it 
must contain one atom of nitrogen (14) and three atoms of hydrogen (3). 

It will also be seen hereafter that the hydrogen in ammonia can be 
replaced by other bodies in thirds, showing that there must be three 
atoms of hydrogen present, whilst the 1 4 parts of nitrogen cannot be re- 
placed in fractions, so that it must represent a single atom. The specific heat 
of hydrogen is found by experiment to be 13*5 times that of nitrogen, so that, 




ESTIMATION OF NITROGEN. 127 

allowing foi errors in determining it, 14 parts of nitrogen may be taken to be 
associated with the same amount of heat as one part of hydrogen (see 8). 

89. Determination of nitrogen in organic substances. — An exact know- 
ledge of the composition of ammonia is of great importance, because the 
general method of ascertaining the proportion of nitrogen present in animal 
and vegetable substances consists in converting that element into ammonia, 
which, being collected and weighed, furnishes by calculation the weight of 
nitrogen present. 

To ascertain the proportion of nitrogen present in an organic substance, a weighed 
quantity of it is mixed with a 
large proportion of soda -lime (a 
mixture of hydrate of soda and 
hydrate of lime), and introduced 
into a tube of German glass (A, 
fig. 150) to which is attached, by 
a perforated cork, a bulb apparatus 
(B) containing hydrochloric acid. 
On heating the tube inch by inch 
with a charcoal or gas furnace, m 150. -Estimation of nitrogen, 

the nitrogen ot the substance is 

evolved in combination with the hydrogen of the hydrates, in the form of ammonia, 
which is absorbed by the hydrochloric acid in the bulbs. When the whole length 
of the tube has been heated, the point (C) is nipped off, and air drawn through by 
applying suction to the orifice (D) of the bulb apparatus, so that all the ammonia 
may be carried into the hydrochloric acid. Its weight is then ascertained, either by 
evaporating the liquid in a weighed dish placed over a steam bath, and weighing the 
hydrochlorate of ammonia, or more accurately by converting it into the double 
chloride of platinum and ammonium. Sometimes a solution of sulphuric acid of 
known strength is substituted for the hydrochloric acid in the bulbs, and the 
weight of the ammonia is ascertained by determining the quantity of acid which 
has been neutralised. 

To illustrate the change which takes place when the organic substance is heated 
with the hydrates of soda and lime, let it be supposed that urea is the substance sub- 
mitted to analysis. 

CH 4 N 2 + Na 2 . H 2 = Na 2 . C0 2 + 2NH3 
Urea. 
The caustic soda alone would be too fusible and would corrode the glass too rapidly. 

In the analysis of an organic substance containing carbon, hydrogen, 
nitrogen, and oxygen, the proportions of carbon and hydrogen having been 
ascertained by the method described at p. 80, and that of nitrogen by the 
process given above, the sum of the carbon, hydrogen, and nitrogen is 
deducted from the entire weight of the substance to obtain the proportion 
of oxygen. The weights thus found are divided by the atomic weights 
of the several elements to obtain the empirical formula, which is converted 
into a rational formula on the principle illustrated at p. 82. 

For example, 10 grs. of urea were found to contain 2 grs. of carbon, 0*66 
gr. of hydrogen, and 4-67 grs. of nitrogen. 

10 grs. of urea minus 7*33 (carbon, hydrogen, and nitrogen) = 2 -67 grs. 
of oxygen. 

Dividing each of these numbers by the atomic weight of the element 
to which it refers, we have, 

2*0 -r- 12 = 0*165 atomic proportion of carbon, 
0-66 - 1 = 0-66 „ „ hydrogen, 

4-67-14 =0-33 „ „ nitrogen, 

2-67 - 16 = 0-165 „ „ oxygen, 

leading to the empirical formula, in its simplest form, CH 4 ^T 2 0, for urea. 
But urea is an organic base, capable of uniting with acids to form salts, 



128 



OXIDATION OF AMMONIA. 



and it is found that to neutralise one molecular weight (36*5 parts) of 
hydrochloric acid, 60 parts of urea are necessary. This quantity would 
contain 12 parts (one atom) of carbon, 4 parts (four atoms) of hydrogen, 
28 parts (two atoms) of nitrogen, and 16 parts (one atom) of oxygen, so 
that the above formula would correctly represent the molecule of urea. 

90. Formation of ammonia in the rusting of iron. — Although free 
nitrogen and hydrogen cannot be made to form ammonia by direct com- 
bination, this compound is produced when the nitrogen meets with hydro- 
gen in the nascent state ; that is, at the instant of its liberation from a 
combined form. Thus, if a few iron filings be shaken with a little water 
in a bottle of air, so that they may cling round the sides of the bottle, 
and a piece of red litmus paper be suspended between the stopper and the 
neck, it will be found to have assumed a blue colour in the course of a 
few hours, and ammonia may be distinctly detected in the rust which is 
produced. It appears that the water is decomposed by the iron, in the 
presence of the carbonic acid of the air and water, and that the hydrogen 
liberated enters at once into combination with the nitrogen, held in 
solution by the water, to form ammonia. 

91. Production of nitrous and nitric acids from ammonia. — If a few 
drops of a strong solution of ammonia be poured into a pint bottle, and 
ozonised air (from the tube for ozonising by induction, fig. 48) be passed 
into the bottle, thick white clouds will speedily be formed, consisting of 
nitrite of ammonia, the nitrous acid having been produced by the oxida- 
tion of the ammonia at the expense of the ozonised oxygen — 

4NH 3 + 6 = 2NH 3 .H 2 O.N 2 3 + 2H 2 0. 

Nitrite of ammonia. 

If copper filings be shaken with solution of ammonia in a bottle of air, 

white fumes will also be produced, together with a deep blue solution 

containing oxide of copper and nitrite of ammonia ; 

the act of oxidation of the copper appearing to have 

induced a simultaneous oxidation of the ammonia. 

A coil of thin platinum wire made round a pencil, 
if heated to redness at the lower end and suspended 
in a flask (fig. 151) with a little strong ammonia at 
the bottom, will continue to glow for a great length 
of time, in consequence of the combination of the 
ammonia with the oxygen of the air taking place at 
its surface, attended with great evolution of heat. 
Thick white clouds of nitrite of ammonia are formed, 
and frequently red vapour of nitrous acid (N 2 3 ) itself. 

If a tube delivering oxygen gas be passed down to the bottom of the flask (fig. 
152), the action will be far more energetic, the heat of the platinum rising to white- 
ness, when an explosion of the mixture of ammonia and 
oxygen will ensue. After the explosion the action will 
recommence, so that the explosion will repeat itself as often 
as may be wished. It is unattended with danger if the ' 
mouth of the flask be pretty large . By regulating the stream 
of oxygen, the bubbles of that gas may be made to burn as 
they pass through the ammonia at the bottom of the flask. 

The oxidation of ammonia may also be shown by the 
arrangement represented in fig. 153. Air is slowly passed, 
from the gas-bag B, through very weak ammonia in the 
bottle a, into a hard glass tube having a piece of red litmus 
paper at b, and a plug of platinised asbestos in the 
centre, heated by a gas-burner ; a piece of blue litmus paper 








COMPOUNDS OF NITROGEN AND OXYGEN. 



129 



is placed at c, and the tube is connected with a large globe (d). The red litmus at b 
is changed to blue by the ammonia, whilst the blue litmus at c is reddened by the 
nitrous acid produced in its oxidation, and clouds of nitrite of ammonia, accompanied 
by red nitrous fumes, appear in d. 




Oxidation of ammonia. 



(The burner represented in the figure is a Bunsen burner (p. 103), surmounted by a 
T-piece with several holes.) 

In the presence of strong bases, and of porous materials to favour oxi- 
dation, ammonia appears to be capable of suffering further oxidation and 
conversion into nitric acid, which combines with the base to form a nitrate, 
thus — 



2STEL + CaO + 0, 



CaO . N 2 5 

Nitrate of lime. 



3H 2 



This formation of nitrates from ammonia is commonly referred to as 
nitrification, and appears to play an important part in the formation of 
the natural supplies of saltpetre which are of so great importance to the 
arts.* 



Compounds of Nitrogen and Oxygen. 

92. Though these elements in their pure state exhibit no attraction for 
each other, five compounds, which contain them in different proportions, 
have been obtained by indirect processes. 

When a succession of strong electric sparks from the induction coil is 
passed through atmospheric air in a flask (especially if the air be mixed 
with oxygen), a red gas is formed in small quantity, which 
is either nitrous acid (N 2 3 ) or nitric peroxide (N0 2 ). 

If the experiment be made in a graduated eudiometer (fig. 154), 
standing over water coloured with blue litmus, the latter will very 
soon be reddened by the acid formed, and the air will be found to 
diminish very considerably in volume, eventually losing its power 
of supporting combustion, in consequence of the removal of oxygen. 




When hydrogen gas, mixed with a small quantity of 
nitrogen, is burnt, the water collected from it is found to 
have an acid taste and reaction, due to the presence of a 
little nitric acid, resulting from the combination of the 
nitrogen with the oxygen of the air under the influence of 
the intense heat of the hydrogen flame. 

Since all the compounds of nitrogen and oxygen are obtained, in prac- 
tice, from hydrated nitric acid, the chemical history of that substance 
must precede that of the oxides of nitrogen. 

* The charcoal which has been used in the sewer ventilators (see p. 64) has been found 
to contain abundance of nitrates. 

I 



130 



PREPARATION OF NITRIC ACID. 



Nitric Acid. 

93. This most important acid is obtained from saltpetre, which is 

found as an incrustation upon 
the surface of the soil in hot 
and dry climates, as in some 
parts of India and Peru. The 
salt imported into this country 
from Bengal and Oude consists 
of nitrate of potash (KN0 3 ), 
whilst the Peruvian or Chilian 
" saltpetre is nitrate of soda 
(NaN0 3 ). Either of these will 
serve for the preparation of 
nitric acid. 




Preparation of nitric acid. 



On the small scale, in the laboratory, nitric acid is prepared by distil- 
ling nitrate of potash with an equal weight of concentrated sulphuric acid. 

In order to make the experiment, four ounces of powdered nitre, thoroughly dried, 
may be introduced into a pint-stoppered retort (fig. 155), and two and a half mea- 
sured ounces of concentrated sulphuric acid poured upon it. As soon as the acid has 
soaked into the nitre, a gradually increasing heat may be applied by means of an 
Argand burner, when the acid will distil over. It must be preserved in a stoppered 
bottle. 

"When the acid has ceased distilling, the retort should be allowed to cool, and filled 
with water. On applying a moderate heat for some time, the saline residue will be 
dissolved. The solution may then be poured into an evaporating dish, and evapo- 
rated down to a small bulk. On allowing the concentrated solution to cool, crystals 
of bisulphate of potash (KHS0 4 ) are deposited, a salt which is very useful in many 
metallurgic and analytical operations. 

The decomposition of nitrate of potash by an equal weight of concen- 
trated sulphuric acid is explained by the equation — 



kno: 


+ H 2 S0 4 = 


HNO, 


+ 


KHS0 4 . 


Nitrate of 


Hydrated 


Hydrated 




Bisulphate of 


potash. 


sulphuric acid. 


nitric acid. 




potash. 



It would appear at first sight that one-half of the sulphuric acid might 
be dispensed with, but it is found that when less sulphuric acid is 

employed, so high a tem- 
perature is required to 
effect the complete decom- 
position of the saltjDetre 
(the above equation then 
representing only the first' 
stage of the action), that 
much of the nitric acid is 
decomposed ; and the neu- 
tral sulphate of potash 
(K 2 S0 4 ), which would be 
the final result, is not nearly 
so easily dissolved out of 
the retort by water as the 
bisulphate. 

For the preparation of 
large quantities of nitric 




Fig. 153. -Preparation of nitric acid. 



acid, the nitrate of soda is substituted for nitrate of potash, being much 
cheaper, and furnishing a larger proportion of nitric acid. 



PROPERTIES OF NITPIC ACID. 131 

The nitrate of soda is introduced into an iron cylinder (A, fig. 156), lined with fire- 
clay to protect it from the action of tte acid, and half its weight of sulphuric acid 
(oil of vitriol) is poured upon it. Heat is then applied by a furnace, into which the 
cylinders are built, in pairs, when the hydrated nitric acid passes off in vapour, and 
is condensed in a series of stoneware bottles (B), surrounded with cold water. 

2NaN0 3 + H 2 S0 4 = K"a 4 S0 4 + 2HNO,. 

Nitrate of n-i n-e-nu-rini Sulphate of Hydrated 

soda. uuoivmioi. sodai nitric acid. 

The sulphate of soda left in the retort is useful in the manufacture of glass. 

In the preparation of nitric acid, it will be observed at the beginning 
and towards the end of the operation, that the retort becomes filled with 
a red vapour. This is due to the decomposition by heat of a portion 
of the colourless vapour of nitric acid, into water, oxygen, and nitric 
peroxide — 

2HX0 3 - H 2 .+ :f 2^s T 2 , 

this last forming the red vapour, a portion of which is absorbed by the 
hydrated nitric acid, and gives it a yellow colour. The pure nitric acid 
is colourless, but if exposed to sunlight it becomes yellow, a portion 
suffering this decomposition. In consequence of the accumulation of the 
oxygen in the upper part of the bottle, the stopper is often forced out 
suddenly when the bottle is opened, and care must be taken that drops 
of this very corrosive acid be not spirted into the face. 

The strongest nitric acid (obtained by distilling perfectly dry nitre 
with an equal weight of pure oil of vitriol, and collecting the middle 
portion of the acid separately from the first and last portions, which are 
somewhat weaker) emits very thick grey fumes when exposed to damp 
air, because its vapour, though itself transparent, absorbs water very 
readily from the air, and condenses into very minute drops of diluted 
nitric acid which compose the fumes. The weaker acids commonly sold 
in the shops do not fume so strongly. An exact criterion of the strength 
of any sample of the acid is afforded by the specific gravity, which may 
be ascertained by the methods described at page 122, using a hydrometer 
adapted for liquids heavier than water. Thus, the strongest acid (HN0 3 ) 
has the specific gravity 1'52;* whilst the ordinary aquafortis or diluted 
nitric acid has the sp. gr. 1*29, and contains only 46*6 per cent, of HNO. r 
The concentrated nitric acid usually sold by the operative chemist (double 
aquafortis) has the sp. gr. 1-42, and contains 67"6 per cent, of HN"0 8 . 

A very characteristic property of nitric acid is that of staining the skin 
yellow. It produces the same effect upon most animal and vegetable 
matters, especially if they contain nitrogen. The application of this in 
dyeing silk of a fast yellow colour may be seen by dipping a skein of 
white silk in a warm mixture of concentrated nitric acid with an equal 
volume of water, and afterwards immersing it in dilute ammonia, which 
will convert the yellow colour into a brilliant orange. When sulphuric 
or hydrochloric acid is spilt upon the clothes, a red stain is produced, and 
a little ammonia restores the original colour; but nitric acid stains are 
yellow, and ammonia intensifies instead of removing them, though it pre- 
vents the cloth from being eaten into holes. 

Mtric acid changes most organic colouring matters to yellow, but, unless 
very concentrated, it merely reddens litmus. If solutions of indigo and 

* It is extremely difficult to obtain the HN0 3 free from any extraneous water, as it 
undergoes decomposition not only when vaporised at the boiling point, but even at ordinary 
temperatures. 



132 ACTION OF NITRIC ACID UFON METALS. 

litmus are warmed in separate flasks, and a little nitric acid added to each, 
the indigo will become yellow and the litmus red. Here the indigo 
(C 8 H 5 NO) acquires oxygen from the nitric acid, and is converted into 
isatine (C 8 H 5 N0 2 ). 

When hydrated nitric acid is heated, it begins to boil at 184° F., but 
it cannot be distilled unchanged, for a considerable quantity is decom- 
posed into nitric peroxide, oxygen, and water, the two first passing off in 
the gaseous form, whilst the water remains in the retort with the nitric 
acid, which thus becomes gradually more and more diluted, until it con- 
tains 68 per cent, of HN0 3 , when it passes over unchanged at the 
temperature of 248° F. The specific gravity of this acid is 1 -42. If an 
acid weaker than this be submitted to distillation, water will pass off 
until acid of this strength is obtained, when it distils over unchanged. 

The specific gravity of the vapour of nitric acid, at 187° F., has been 
determined as 29-6 (H=l), which is sufficiently near to half of 63 to 
show that the molecule HN0 3 would occupy exactly two volumes if it 
had not suffered partial decomposition by heat. 

The facility with which hydrated nitric acid parts with a portion of its 
oxygen, renders it very valuable as an oxidising agent. Comparatively 
few substances which are capable of forming compounds with oxygen can 
escape oxidation when treated with nitric acid. 

A small piece of phosphorus dropped into a porcelain dish containing 
the strongest nitric acid (and placed at some distance to avoid danger), 
soon begins to act upon the acid, generally with such violence as to burst 
out into flame, and sometimes to shatter the dish ; the result of this action 
is hydrated phosphoric acid, the same compound which is formed in the 
anhydrous state, when phosphorus is burnt in oxygen gas. 

When sulphur is heated with nitric acid, it is actually oxidised to a 
greater extent than when burnt in pure oxygen, for in this case it is con- 
verted into sulphurous acid (S0 2 ), whilst nitric acid imparts to it three 
atoms of oxygen, forming sulphuric acid (S(X). 

Charcoal, which is so unalterable by most chemical agents at the 
ordinary temperature, is oxidised by nitric acid. If the strongest nitric 
acid be poured upon finely powdered charcoal, the latter takes fire at 
once. 

Even iodine, which is not oxidised by free oxygen, is converted into 
iodic acid (I 2 5 ) by nitric acid. 

It not unfrequently happens in this manner that oxygen, in a state of 
unstable combination, is more prone to unite with other substances than 
when it is in a free state. It would seem that the disposition to com- 
bination having been once impressed upon it is retained, so as to facilitate 
its union with other bodies. 

Eut it is especially in the case of metals that the oxidising powers of 
nitric acid are called into useful application. 

Acids are not capable of forming salts with metals, but only with their 
oxides. Hence, when a metal is dissolved by any oxygen acid, the 
latter must first convert the metal into an oxide, which then acts upon 
the acid to form a salt. 

For the purpose of facilitating the explanation of the action of nitric 
acid upon metals, it will be found convenient to represent the hydrated 
nitric acid by the formula H,O.N" 2 5 ( = 2HN0 3 ), for which it will be 
presently seen that some justification is afforded by the fact that it may 
be produced by dissolving anhydrous nitric acid (IST 2 5 ) in water. 



ACTION OF NITHIC ACID UPON METALS. 133 

If a little Mack oxide of copper be heated in a test-tube with nitric 
acid, it dissolves, without evolution of gas, yielding a blue solution, which 
contains the nitrate of copper. In this case the oxide of copper may be 
represented as having simply displaced the water of the hydrated acid — 

CuO + H 2 O.NA = H 2 + CuO.N 2 5 . 

Oxide of copper. Nitrate of copper. 

But when nitric acid is poured upon metallic copper (copper turnings), 
a very violent action ensues, red fumes are abundantly evolved, and the 
metal dissolves in the form of nitrate of copper — 

4(H 2 O.N 2 5 ) + Cu 3 = 3(CuO.N a 5 ) + 4H 2° + 2N0 • 

Nitrai e of copper. Nitric oxiie. 

The nitric oxide itself is colourless, but as soon as it comes into contact 
with the oxygen of the air, it is converted into the red nitric peroxide, 
NO + = N0 2 . 

All the metals in common use are acted upon by nitric acid, except 
gold and platinum, so that this acid is employed to distinguish and 
separate these metals from others of less value. The ordinary ready 
method of ascertaining whether a trinket is made of gold consists in 
touching it with a glass stopper wetted with nitric acid, which leaves 
gold untouched, but colours base alloys blue, from the formation of 
nitrate of copper. The touchstone allows this mode of testing to be 
applied with greater accuracy. It consists of a species of black basalt, 
obtained chiefly from Silesia. If a piece of gold be drawn across its sur- 
face, a golden streak is left, which is not affected by moistening with 
nitric acid; whilst the streak left by brass, or any similar base alloy, 
would be rapidly dissolved by the acid. Experience enables an operator 
to determine by means of the touch-stone pretty nearly the amount of 
gold present in the alloy, comparison being made with the streaks left by 
allo} 7 s of known composition. 

Though all the metals in common use, except gold and platinum, are oxidised by 
nitric acid, they are not all dissolved; there are two metals, tin and antimony, which 
are left by the acid in the state of insoluble oxides, which possess acid properties, 
and do not unite with the nitric acid. 

If some concentrated nitric acid he poured upon tin filings, no action will be 
observed ; * but on adding a little water, red fumes will be evolved in abundance, 
and the tin will be converted into a white powder, which is the binoxide of tin 
(Sn0 2 ), putty powder. The gas which is evolved in this case is the nitric peroxide 
(N0 2 ), and the action of the acid is represented by the equation which follows :— 

2(H 2 . N 2 5 ) + Sn = Sn0 2 + 2H 2 + 4N0 2 . 

If the white mixture of binoxide of tin with nitric acid be made into a paste with 
slaked lime, the smell of ammonia will be exhaled; and experiments with other 
metals have shown it to be a general principle, that when any metal capable of 
decomposing water is dissolved in diluted nitric acid, ammonia is always formed, its 
quantity increasing with the degree of dilution of the nitric acid ; of course, the 
ammonia combines with the excess of acid present to form nitrate of ammonia, and 
the lime was added in the above experiment in order to displace the ammonia from 
its combination, and to exhibit its odour. This conversion of nitric acid into 
ammonia becomes the more interesting when it is remembered that the ammonia 
can be reconverted into nitric acid (p. 129). 

By dissolving zinc in very diluted nitric acid, a very large quantity of ammonia 
may be obtained. The change is easily followed if we suppose the nascent hydrogen 

* It is a fact which has scarcely been explained in a satisfactory manner, that the con- 
centrated nitric acid often refuses to act upon metals which are violently attacked by the 
diluted acid. 



134 ACTION OF NITRIC ACID ON ORGANIC SUBSTANCES. 

(or hydrogen with the tendency to combination still remaining impressed upon it, 
see p. 132), produced by the action of the zinc upon the water, to act upon the nitric 
acid, converting its oxygen into water, and its nitrogen into ammonia, thus — 
HN0 3 + H 8 = 3H 2 + NH 3 . The exalted attractions possessed by substances in 
the nascent state, that is, at the instant of their passing from a state of combination, 
are very remarkable, and will be found to receive frequent application.* 

Action of nitric acid upon organic substances. — The oxidising action 
of nitric acid upon some organic substances is so powerful as to be 
attended with inflammation ; if a little of the strongest nitric acid be 
placed in a porcelain capsule, and a few drops of oil of turpentine be 
poured into it from a test-tube fixed to the end of a long stick, the tur- 
pentine takes fire with a sort of explosion. By boiling some of the 
strongest acid in a test-tube (fig. 157), the mouth of which is loosely 
stopped with a plug of raw silk or of horse-hair, the latter may be made 
to take fire and burn brilliantly in the vapour of nitric acid. 

In many cases the products of the action of nitric acid exhibit a most 
interesting relation to the substances from which they have been pro- 
duced, one or more atoms of the hydrogen of 
the original compound having been removed 
in the form of water by the oxygen of the nitric 
acid, whilst the spaces thus left vacant have been 
filled up by the nitric peroxide resulting from 
the deoxidation of the nitric acid, producing 
what is termed a nitro-substitution compound. 
A very simple example of this displacement of 
H by ]ST0 2 is afforded by the action of nitric 
acid upon benzole. A little concentrated nitric 
Y\». 157. ac ^ i s placed in a flask, and benzole cautiously 

dropped into it ; a violent action ensues, and the 
acid becomes of a deep red colour ; if the contents of the flask be now 
poured into a large vessel of water, a heavy yellow oily liquid is separated, 
having a powerful odour, like that of bitter almond oil. This substance, 
which is used to a considerable extent in perfumery under the name of 
essence of mirbane, is called nitro-benzole, and its formula, C 6 H 5 (ISr0 2 ), at 
once exhibits its relation to benzole, C 6 H 6 .t 

But the change does not stop here, for by continuing the action of the 
acid, dinitro-benzole C 6 H 4 2(N0 2 ) is obtained, in which two atoms of 
hydrogen have been displaced by nitric peroxide. 

It is by an action of this description that nitric acid gives rise to gun- 
cotton, and other explosive substances of the same class, when acting upon 
the different varieties of woody fibre, as cotton, paper, sawdust, &c. 

The preparation and composition of gun-cotton will be described here- 
after. 

94. The oxidising effects of nitric acid are not confined to the free acid, 
but are shared to some extent by the nitrates. A mixture of nitrate of 

* When a solution of nitrate of potash is mixed with a strong solution of caustic potash, 
and heated with granulated zinc, ammonia is abundantly disengaged, being produced from 
the nitric acid by the nascent hydrogen resulting from the action of the zinc upon the 
caustic potash. 

Recent experiments have indicated the existence of substances intermediate between 
+he nitric acid and the ammonia into which it is finally converted. One of these, named 
hydroxy iamine, NH 3 0, has been examined. It is a well-defined base, forming crystalline 
salts with the acids. 

| C fi H 6 + HNO3 = C 6 H,(N0 2 ) + H 2 0. 
C 6 H„ + 2(HN0 3 ) =C 6 H 4 2(N0 2 ) + 2H 2 0. 




NITRATES. 135 

lead with charcoal explodes when sharply struck, from the sudden evolu- 
tion of carbonic acid produced by the oxidation of the carbon. If a few 
crystals of nitrate of copper be sprinkled with water and quickly wrapped 
up in tin-foil, the latter will, after a time, be so violently oxidised as to 
emit brilliant sparks. 

But in the case of bases which retain the nitric acid with greater force, 
such as the alkalies, the oxidation takes place only at a high tempera- 
ture. If a little nitre be fused in an earthen crucible or an iron ladle, 
and, when it is at a red heat, some powdered charcoal, and afterwards 
some flowers of sulphur, be thrown into it, the energy of the combustion 
will testify to the violence of the oxidation. In this manner the carbon 
is converted into carbonate of potash (K 2 O.C0 2 ), and the sulphur into 
sulphate of potash (K 2 O.S0 3 ). See Gunpowder. 

Combining weight of nitric acid. — Experiment proves that 56 parts by 
weight (1 molecule) of caustic potash are neutralised by 63 parts of hy- 
drated nitric acid, and this quantity of the acid is found to contain 1 part 
of hydrogen, 14 parts of nitrogen, and 48 parts (3 atoms) of oxygen. 
Hence the formula of the acid is written HN0 3 . 

95. Anhydrous nitric acid or nitric anhydride (N 2 5 ) is obtained by gently heating 
nitrate of silver in a slow current of chlorine, great care being taken to exclude every 
trace of water — 

Ag 2 O.N 2 5 + Cl 2 = 2AgCl + + N 2 5 . 
Nitrate of silver. Chloride of silver. Nitric anhydride. 

The anhydride is condensed as a crystalline solid in a receiver cooled with ice and 
salt. It forms transparent colourless prisms which liquefy at 85° F., and boil at 113°. 
By a slightly higher temperature it is readily decomposed ; and it has been said to 
decompose, even at the ordinary temperature, in sealed tubes which were shattered 
by the evolved gas. 

When the anhydride is brought in contact with water, much heat is evolved, and 
hydrated nitric acid is produced. 

The specific gravity of the vapour of anhydrous nitric acid being unknown, it is 
only a surmise that its molecule is represented by N 2 6 . Its formation by the 
action of chlorine upon nitrate of silver appears to take place in two stages ; (1) 
Ag.N0 2 .0 + Cl 2 = AgCl + N0 2 C1 {chloride of azotyle) + and (2) N0 2 C1 + 
Ag.N0 2 .0 = AgCl + N0 2 .N0 2 .0 (anhydrous nitric acid.) 

The disposition of HN0 3 to give N0 2 as a product of its decomposition, and to 
exchange it for the hydrogen of organic substances, leads to the belief that it is really 

formed upon the type of a molecule of water „ [ 0, in which half the hydrogen is 

displaced by N0 2 . The relation between the anhydrous and the hydrated acid and 

the nitrates would then be a very simple one ; anhydrous nitric acid, -^-q 2 i ; 

hydrated nitric acid, ^^ [ ; saltpetre, -^^ [0. 

Nitrates. — Its attraction for bases places nitric acid among the strongest 
of the acids, though the disposition of its elements to assume the gaseous 
state at high temperatures, conjoined with the feeble attraction existing 
between nitrogen and oxygen, causes its salts to be decomposed, without 
exception, by heat. 

The nature of the decomposition varies with the base contained in the 
nitrate. The nitrates of very powerful bases (such as the alkalies) are 
first converted into nitrites by the action of heat ; thus K 2 O.N 2 5 gives 
K 2 O.N 2 3 and 2 ; the nitrites themselves being eventually decomposed, 
evolving nitrogen and oxygen, and leaving the uncombined base. The 
nitrates of feebler bases (such as oxide of copper and oxide of lead) evolve 
nitric peroxide (N0 2 ) and oxygen, the base being left, unless it be decom- 



136 



NITROUS OXIDE. 



posible by heat, as is the case with the oxides of silver and mercury, when 
the metal itself will be separated. As a general rule, the nitrates are 
easily soluble in water. 

As in the case of the carbonates, the nitrates may be represented either 
by substitutive formulae, representing them as derived from one or more 
molecules of HN0 3 by the substitution of metals for the hydrogen, or by 
additive formulae, as composed of the metallic oxides combined with the 
anhydrous nitric acid N 2 5 . Generally speaking, the additive formulae 
are more convenient for explaining the decompositions in which these 
salts take part. 

Comparatively few of the nitrates are in common use ; the following 
table contains those most frequently used : — 



Chemical Name. 


Common Name. 


Additive Formula. 


Substitutive Formula. 


Nitrate of pot 
ash 

Nitrate of soda 

Nitrate of stron- 
tia 

Basic nitrate of 
bismuth 

Nitrate of silver 


[ Nitre, saltpetre 

{ Cubic nitre ) 
( Peruvian saltpetre ) 

i Nitrate of strontian 

( Trisnitrate of bis- ) 
< muth y 
( Flake white ) 
Lunar caustic 


K 2 O.N 2 5 

Na 2 . N 2 5 
SrO . N 2 5 

Bi 2 3 . N 2 5 . H 2 
Ag 2 O.N 2 5 


KN0 3 

NaN0 3 
Sr(N 3 ) 2 

AgN0 3 



96. Nitrous oxide or laughing gas (N 2 = 44 parts by weight = 2 vols.) 
is prepared by heating nitrate of ammonia, when it is resolved into water 
and nitrous oxide.* 



NIL . M"0. 



2B\0 + KO 



Nitrate of ammonia is obtained by adding fragments of carbonate of ammonia to 
nitric acidf diluted with an equal volume of water, until the carbonate no longer 
effervesces in the liquid, which is then evaporated down until a drop solidifies on a 
cold surface, when the whole may be poured out upon a clean stone, and the mass 
broken up and preserved in a well-stoppered bottle, because it is liable to attract 
moisture from the air. To obtain the nitrous oxide, an ounce of the salt may be 
gently heated in a small retort, when it melts, boils, and gradually disappears 
entirely in the forms of steam and nitrous oxide. The latter may be collected, with 
slight loss, over water. 

Nitrous oxide is perfectly colourless, but has a slight odour and a 
sweetish taste. Its characteristic intoxicating property is well known. 
It accelerates the combustion of a taper like oxygen itself, and will 
even kindle into flame a spark at the end of a match. It can 
readily be distinguished from oxygen, however, by shaking it with water, 
which absorbs, at the ordinary temperature, about three-fourths of its 
volume of the nitrous oxide. It is also much heavier than oxygen, its 
specific gravity being 153, and is not a permanent gas, being liquefied 
by a pressure of 40 atmospheres at 45° F., and solidified at -150° F. 
It is now sold in a liquid state in wrought iron vessels for use as an 
anaesthetic in dental surgery. 

* By passing the mixture of nitrous oxide and aqueous vapour over hydrate of potash at 
a dull red heat, nitric acid and ammonia are reproduced. 

f Which must remain clear when tested with nitrate of silver, showing it to be free from 
chlorine. 



NITRIC OXIDE. 



137 



The liquid nitrous oxide possesses properties similar to those of liquid carbonic 
acid with respect to its rapid evaporation ; but it may be drawn into test-tubes in a 
liquid state from the receiver. A lighted match thrown into the liquid burns with 
great brilliancy. When mixed with bisulphide of carbon and evaporated in vacuo, 
it produces the lowest temperature hitherto obtained — 220° F. 

97. Nitric oxide (NO = 30 parts by weight = 2 vols.) is usually 
obtained by the action of copper upon diluted nitric acid — 



4(H 2 O.N 2 5 ) + Cu 3 = 3(CuO.K,0 5 ) + 2M) 



4H 2 




300 grains of copper turnings or clippings are introduced into a retort, and three, 
measured ounces of a mixture of 
concentrated nitric acid with an 
equal volume of water are poured 
upon them. A very gentle heat 
may be applied to assist the 
action, and. the gas may be col- 
lected over water (see fig. 158), 
which absorbs the red fumes 
(N0 2 ) formed by the union of the 
NO with the air contained in the 
retort. 

Nitric oxide is distinguish- 
ed from all other gases by the - 
production of a red gas, when ■== 
the colourless nitric oxide is 
allowed to come in contact 
with uncombined oxygen, the presence of which, in mixtures of gases, may 
be readily detected by adding a little nitric oxide. The red gas consists 
chiefly of nitric peroxide (N0. 2 ), but it often contains also some (N 2 3 ) 
nitrous acid. 

The combination of nitric oxide with oxygen may be exhibited by decanting a pint 
bottle of oxygen, under water, into a tall jar filled with water coloured with blue 
litmus, and adding to it a pint bottle 
of nitric oxide (fig. 159). Strong 
red fumes are immediately produced, 
and on gently agitating the cylin- 
der, the fumes are absorbed by the 
water, reddening the litmus. The 
oxygen will now have been reduced 
to half its volume, and if another 
pint of nitric oxide be added, the 
remainder of the oxygen will be 
absorbed, showing that tv)o volumes 
of nitric oxide combine with one volume 
of oxygen, forming the nitric per- 
oxide which is absorbed by the 
water. 

The addition of nitric oxide 
to atmospheric air was one of 
the earliest methods employed 
for removing the oxygen in 
order to determine the composition of air ; but important variations were 
observed in the results, in consequence of the occasional formation of N 2 3 
in addition to the JST0 2 . 

_ The rough analysis of air by this method may be instructively performed with two 
similar gas cylinders, each divided into ten equal volumes. Into one are introduced 
five volumes of air, and into the other five volumes of nitric oxide. On decanting 




Fig. 159. 



138 



PROPERTIES OF NITRIC OXIDE. 




the air, under water, into the nitric oxide (fig. 160), the red nitric peroxide will be 

formed and absorbed by the water, the 
ten volumes of gas shrinking to seven, 
showing that three volumes have been 
absorbed, of which one volume would of 
course represent the oxygen contained 
in the five volumes of air. 

The nitric oxide prepared by the action 
of copper on nitric acid generally con- 
tains nitrous oxide, and will seldom give 
correct results in the above experiment. 
Pure nitric oxide may be obtained by 
heating in a retort 100 grains of nitrate 
of potash, 1000 grains of sulphate of iron, 
and three measured ounces of diluted 
sulphuric acid (containing one measure 

of acid to three measures of water), which will yield above two pints of the gas.* 

Ill all its properties, nitric oxide is very different from nitrons oxide. 
It is much lighter, having almost exactly the same specific gravity as air, 
viz., 1-04, has never yet been liquefied, and is not dissolved to any impor- 
tant extent by water. When a lighted taper is immersed in nitric oxide, 
it is extinguished, although this gas contains twice as much oxygen as 
nitrous oxide, which so much accelerates the combustion of a taper ; for 
the elements are held together by a stronger attraction in the nitric oxide, 
so that its oxygen is not so readily available for the support of combus- 
tion. (The nitric oxide prepared from copper and nitric acid sometimes 
contains so much nitrous oxide that a taper burns in it brilliantly.) 
Even phosphorus, when just kindled, is extinguished in nitric oxide, 
but when allowed to attain to full combustion in air, it burns with ex- 
treme brilliancy in the gas. Indeed, nitric oxide appears to be the least 
easy of decomposition of the whole series of oxides of nitrogen, which 
accounts for it being the most common result of the decomposition of 
the other oxides. ' Nitrous oxide itself, when passed through a red-hot 
tube, is partly converted into nitric oxide ; and when a taper burns in a 
bottle of nitrous oxide, the upper part of the bottle is often filled with a 

red gas, indicating the formation 
of nitric oxide, and its oxidation 
by the air entering the bottle. 

The difference in the stability of 
the two gases is also shown by 
their behaviour with hydrogen. 
A mixture of nitrous oxide with 
an equal volume of hydrogen ex- 
plodes when in contact with flame, 
yielding steam and nitrogen, but 
a mixture of equal volumes of 
nitric oxide and hydrogen burns 
quietly in air, the hydrogen not 
decomposing the nitric oxide. An 
excess of hydrogen, however, is 
capable of decomposing nitric oxide, ammonia and water being formed. 

If two volumes of nitric oxide be mixed with five volumes of hydrogen, and the 
gas passed through a tube having a bulb filled with platinised asbestos (fig. 161),+ 

* K O.N„0 5 + 6(FeO.S0 3 ) + 4(H 2 O.S0 3 ) = K 2 O.S0 3 + 3(Fe 2 3 .3S0 3 ) + 2NO + 4H 2 0. 
f Asbestos which has been wetted with solution of bichloride of platinum, dried, and 
heated to redness, to reduce the platinum to the metallic state. 




161. 



NITROUS ACID. 



139 



the mixture issuing from the orifice of the tube will produce the red vapours, by 
contact with the air, which will strongly redden blue litmus ; but if the platinised 
asbestos be heated with a spirit-lamp, the hydrogen, encouraged by the action 
of the platinum (91) will decompose the nitric oxide, and strongly alkaline vapours 
of ammonia will be produced, restoring the blue colour to the reddened litmus : 
NO + H 5 = NH 3 + H 2 0. It will be remembered that when oxygen is in excess, 
ammonia is converted, under the influence of platinum, into water and nitrous acid (91). 

Nitric oxide is readily absorbed by ferrous salts (salts of protoxide of 
iron) with which it forms dark brown solutions. If a little solution of 
sulphate of iron be shaken in a cylinder of nitric oxide closed with a glass 
plate, the gas will be immediately absorbed, and the solution will become 
dark brown. On applying heat, the brown compound is decomposed. 
A compound of 4 molecules of ferrous sulphate and one molecule of nitric 
oxide has been obtained in small brown crystals, which lose all their 
nitric oxide in vacuo. 

98. Nitrous acid (N 2 3 = 76 parts by weight).* — This acid is said 
to exist, as nitrite of ammonia, in minute quantity, in rain water, and is 
occasionally found in combination with alkalies or alkaline earths, in 
well-waters, where it has probably been formed by the oxidation of am- 
monia (91). Small quantities of nitrite of ammonia appear to be formed 
by the combustion in air of gases containing hydrogen, this element 
uniting with the atmospheric oxygen and nitrogen. 

Nitrous acid may be obtained by heating starch with nitric acid, but 
the most convenient process consists in gently heating nitric acid (sp. 
gr. 1*35) with an equal weight of arsenious acid, and passing the gas, first 
through a XJ-tube (fig. 162) surrounded with cold water, to condense un- 




Preparation of nitrous acid. 



decomposed nitric acid, then through a similar tube containing chloride 
of calcium, to absorb aqueous vapour, and afterwards into a U-tube sur- 
rounded with a freezing mixture of ice and salt. Through a small tube 
opening into the bend of this U-tube, the condensed nitrous acid drops 
into a tube drawn out to a narrow neck, so that it may be drawn off, and 
sealed by the blowpipe. 

H 2 O.N 2 5 + As 2 3 = H 2 O.As 2 5 + tf 2 3 . 

Arsenious acid. Arsenic acid. 

The nitrous acid is thus obtained as a blue liquid which boils below 
32° F., becoming converted into a red vapour, and partly decomposed 
into NO and NO„. Water at about 32° F. dissolves the acid without 



* The specific gravity of nitrous acid not having been ascertained on account of its want 
of stability, the formula N 2 3 is only provisionally assigned to the molecule. 



140 BKOPEKTIES OF N1TKIC PEROXIDE. 

decomposing it, yielding a blue solution which is decomposed, as the 
temperature rises, into nitric acid which remains in the liquid, and nitric 
oxide which escapes with effervescence — 

3N 2 3 + H 2 = II 2 O.N 2 5 + 4NO. 

A very dilute solution of nitrous acid may be preserved for some time 
without decomposition. 

The salts of nitrous acid, or nitrites, are interesting on account of their 
production from the nitrates by the action of heat (p. 135). 

If nitrate of potash be fused in a fire-clay crucible and heated to redness, it will 
evolve bubbles of oxygen, and slowly become converted into nitrite of potash 
(K 2 O.N 2 3 ). The heat should be continued until a portion removed on the end of 
an iron rod, and dissolved in water, gives a strongly alkaline solution. The fused 
mass may then be poured upon a dry stone, and when cool, broken into fragments 
and preserved in a stoppered bottle. On heating a fragment of the nitrite of potash 
with diluted sulphuric acid, red vapours will be disengaged, but these contain little 
nitrous acid, the greater part of this being decomposed by the water into nitric acid 
and nitric oxide. 

When nitrous acid acts upon ammonia, both compounds suffer decomposition, 
water and nitrogen being the results — 

2NH 3 + N 2 3 = N 4 + 3H 2 . 

This is sometimes taken advantage of in preparing nitrogen gas by boiling mixed 
solutions of sal-ammoniac and nitrite of potash — 

2(NH 3 .HC1) + K 2 O.N 2 3 = N 4 + 2KC1 + 4H 2 . 

Sal-ammoniac. 

In experiments upon organic compounds, nitrous acid is sometimes employed as 
a convenient agent for effecting simultaneously the removal of three atoms of hydro- 
gen from a compound, and the insertion of one atom of nitrogen. 

"When solutions of nitrites are heated in contact with air, they gradually absorb 
oxygen, becoming converted into nitrates. 

99. Nitric peroxide (N0 2 = 46 parts by weight = 2 vols.), also 
called hyponitric acid and peroxide of nitrogen or pernitric oxide : for- 
merly known as nitrous acid. — By passing a mixture of nitric oxide with 
half its volume of oxygen, free from every trace of moisture, into a per- 
fectly dry tube cooled in a mixture of ice and salt, the dark red gas is 
condensed into colourless prismatic crystals, which melt at 10° F. into 
a nearly colourless liquid. This gradually becomes yellow as the temper- 
ature rises, and at the ordinary temperature has a deep orange colour. 
It is very volatile, boiling at 71° F., and being converted into a red- 
brown vapour, which was long mistaken for a permanent gas, on account 
of the great difficulty of condensing it when once mixed with air or 
oxygen. Nitric peroxide is also obtained, mixed with one-fourth of its 
volume of oxygen, by heating the nitrate of lead (fig. 163) — 
PbO.N 2 5 - PbO + 2N0 2 + 0. 

The vapour of nitric peroxide is much heavier than atmospheric air. 

Its specific gravity (compared with hydrogen at the same temperature) diminishes 
as the temperature rises. At 275° F. it is 23 times as heavy 
as hydrogen, showing its molecular weight to be 46. This 
variation in density, in conjunction with the other changes, 
with increase of temperature, lead to the belief that the mole- 
cule of nitric peroxide, at low temperatures (in its liquid 
state), is N 2 ^4) an( l becomes decomposed into 2N0 2 at high 
temperatures. 

Its colour varies with the temperature, becoming 

very dark at 100° F. The smell of the vapour is 

very characteristic. It supports the combustion of 
Fig. 163.— Preparation J , , i T x, i, i 

Sf nitric peroxide. strongly burning charcoal or phosphorus, and 




PROPERTIES OF NITRIC PEROXIDE. 141 

oxidises most of the metals, potassium taking fire in it spontaneously. 
The nitric peroxide must, therefore, rank as a powerful oxidising agent, 
and it is the presence of this substance in the red fuming nitric acid 
that imparts to it higher oxidising powers than those of the colourless 
nitric acid. 

The so-called nitrous acid of commerce is really nitric acid holding in 
solution a large proportion of nitric peroxide, and is prepared by intro- 
ducing sulphur into the retorts containing the mixture of nitrate of soda 
and sulphuric acid employed in the preparation of the nitric acid, a por- 
tion of which is deoxidised and converted into nitric peroxide. Water 
immediately decomposes the nitric peroxide into nitric oxide and nitric 
acid — 

3N0 2 + H 2 = NO + 2HN0 3 . 

When water is gradually added to liquid nitric peroxide, it effervesces, 
from escape of nitric oxide, and becomes green, blue, and ultimately 
colourless. The production of the green and blue colours appears 
to be due to the formation of N 2 3 in an intermediate decomposition ; 
2N 2 4 + H 2 = N 2 3 + 2HN0 3 j an( ^ wnen this is decomposed 
by an excess of water, the liquid, of course, becomes colourless. If the 
red nitric acid of commerce be gradually diluted with water, it will 
be found to undergo similar changes, always becoming colourless at last. 
The nitric acid which has been used in a Grove's battery always has a 
green colour from the large amount of nitric peroxide which has 
accumulated in it, in consequence of the decomposition of the acid 
by the hydrogen disengaged during the action of the battery ; 
H + HN0 3 = H 2 + N0 2 . If this green acid be diluted with 
a little water, it becomes blue, and a larger quantity of water renders 
it colourless, causing the evolution of nitric oxide. Similar colours are 
obtained by passing nitric oxide into nitric acid of different degrees of 
concentration, apparently because nitric peroxide is formed and dissolved 
by the acid — 

NO + 2(HN0 3 ) = 3N0 2 + H 2 0. 

When silver, mercury, and some other metals are dissolved in cold nitric 
acid, a green or blue colour is often produced, leading a novice to suspect 
the presence of copper, the colour being really caused by the solution in 
the unaltered nitric acid of the nitric peroxide produced by the deoxida- 
tion of another portion. 

Nitric peroxide was formerly believed to be an independent acid 
capable of forming salts. It is true that its vapours have a strongly acid 
reaction to test-papers, but when brought into contact with bases, it pro- 
duces a mixture of nitrate and nitrite — 

2N 2 4 + 2(KO.H 2 0) - K 2 O.N 2 5 + K 2 O.N 2 3 + 2H. 2 . 

100. General review of the oxides of nitrogen. — All the above oxides of 
nitrogen are directly obtainable from nitric acid by the action of metals ; 
but since the result of such action varies much with the temperature and 
state of concentration of the acid, it cannot be depended upon for the 
preparation of the oxides in a separate state. 

Nitric peroxide is the chief product of the action of tin upon nitric 
acid — 

2(H 2 O.N 2 5 ) + Sn = 2H 2 + 4N0 2 + Sn0 2 .' 



142 GENERAL SUMMARY OF OXIDES OF NITROGEN. 

Nitrous acid is abundantly formed when silver is acted on by nitric acid — 

3(H 2 O.N 2 5 ) + Ag 4 = 3H 2 + N 2 3 + 2(Ag 2 O.N 2 5 ), 

Nitric oxide has been shown to be evolved when nitric acid is deoxidised 
by copper — 

4(H 2 O.N 2 5 ) + Cu 3 = 4H 2 + 2NO + 3(CuO . N 2 5 ) ; 

though, if the acid be concentrated or the temperature high, nitrous oxide 
and nitrogen are mixed with the nitric oxide. 

Nitrous oxide is given off when zinc is dissolved in nitric acid diluted 
with ten measures of water — 

5(H 2 O.N 2 5 ) + Zn 4 = 5H 2 + N 2 + 4(ZnO.N 2 5 ); 

the nitrous oxide, however, is mixed with nitric oxide. 

Nitric oxide, nitrous acid, and nitric peroxide, are very remarkable for 
their relations to oxygen. Nitric oxide is one of the very few substances 
which combine with dry oxygen at the ordinary temperature, and yet the 
nitric peroxide which is thus produced is very ready to yield its oxygen 
to other substances. Nitrous acid, as might be expected, is intermediate 
in this respect, being capable of acting as a reducing agent upon power- 
fully oxidising substances, and as an oxidising agent upon substances 
having a great attraction for oxygen. Thus, a solution of nitrite of 
potash, acidified with sulphuric acid, will bleach permanganate of potash, 
reducing the permanganic acid (Mn 2 7 ) to manganous oxide (MnO ; 
whilst, if added to sulphate of iron, the nitrite converts the ferrous oxide 
(EeO) into ferric oxide (Te 2 3 ), and this solution, which was capable of 
reducing the permanganate of potash before, is now found to be without 
effect upon it, unless an excess of the nitrite has been added. 

The oxides of nitrogen, as illustrating combination in multiple propor 
lions by weight and- volume. — In its most general form, the law of multiple 
proportions may be thus stated. When a substance (A) combines with 
another subsLtin^p. (B) in more than one proportion, the quantities of B, 
which combine with a constant quantity of A, are multiples of the 
smallest combining quantity of B by some whole number. 

In the oxides of nitrogen this law is exemplified in the simplest form, 
since the quantities of oxygen which combine with a constant quantity of 
nitrogen, are multiples of the least combining quantity of oxygen by 2, 



, 4, and 5. 












N. 


0. 


Nitrous oxide, ... 


. N 2 


28 


16 


Nitric oxide (two molecules), 


• ^ 2 o 2 


28 


16 X 2 


Nitrous acid, 


• N a 8 


28 


16 X 3 


Nitric peroxide, . 


. . N 2 4 


28 


16 X 4 


Nitric acid, .... 


• n 2 o 5 


28 


16 X 5 



It was shown, at p. 126, that there is ground for representing the atomic weight of 
nitrogen as = 14. 

When nitrous oxide is passed through a red-hot porcelain tube, its volume is 
increased by one-half, and the resulting gas is found to be a mixture of one volume 
of oxygen and two volumes of nitrogen. Hence it is inferred that, in nitrous oxide, 
two volumes or atoms (28 parts) of nitrogen are united with one volume or atom (16 
parts) of oxygen, to form two volumes or one molecule of nitrous oxide (representing 
44 parts by weight). 

When charcoal is strongly heated in nitric oxide, the volume of the gas remains 
unchanged ; but it is found, on analysis, to have become converted into a mixture of 
equal volumes of carbonic acid and nitrogen (2N0 + C = C0 2 + N 2 ). Since one 
volume of carbonic acid contains one volume of oxygen (page 88), the experiment 



CHLORINE. 143 

proves that one volume of oxygen and one volume of nitrogen exist in two volumes of 
nitric oxide, or that one atom of nitrogen (or 14 parts) is combined with one atom of 
oxygen (16 parts) in two volumes (one molecule, or 30 parts by weight) of nitric 
oxide. 

The direct evidence of the composition of nitrous acid is not so satisfactory as that 
in the two preceding cases. This acid has been obtained, however, by the direct 
union of one volume of oxygen with four volumes of nitric oxide, leading to the con- 
clusion that it contains N 2 3 . Its molecular weight has been determined by the 
analysis of nitrite of silver, which was found to contain, for one molecule (232 parts 
by weight) of oxide of silver, 76 parts by weight of nitrous acid, representing a com- 
pound of 28 parts by weight of nitrogen (or two atoms = 2 volumes), with 48 parts 
by weight (or three atoms = 3 volumes) of oxygen. The volume occupied by the 
molecule of nitrous acid in the state of vapour has not yet been ascertained, no accu- 
rate determination of the specific gravity of its vapour having been made. 

Nitric peroxide has been analysed by passing the vapour produced from a known 
weight of the liquid over red-hot metallic copper, which absorbed the oxygen, leaving 
the nitrogen to be collected and measured. It was thus found that 14 parts by weight 
(one atom = 1 volume) of nitrogen were combined with 32 parts by weight (two 
atoms = 2 volumes) of oxygen, a result which is confirmed by the direct union of 2 
volumes of NO (one molecule) with 1 volume of oxygen (one atom) to form N0 2 . 

Nitric anhydride, or anhydrous nitric acid, was analysed by a method similar to 
that employed for nitric peroxide, and was found to contain 28 parts by weight (two 
atoms) of nitrogen, combined with 80 parts (five atoms) of oxygen. The volume 
occupied by the molecule of nitric anhydride in the state of vapour has not been 
determined, on account of the want of stability of this compound. 

The facility with which nitrous acid and nitric peroxide can be decomposed with 
formation of nitric oxide, renders it probable that they really contain that compound. 
To express this, they may plausibly be represented as formed after the same plan as a 

molecule of water. Just as in rr 0, the two atoms of hydrogen are linked together 

by the diatomic oxygen, so in nitrous acid, -v^q > 0, two molecules of nitric oxide are 
linked together by the atom of oxygen, whilst in nitric peroxide (N 2 4 ) a molecule 
of NO is bound up with a molecule of N0 2 , thus ^q I 0. If nitric acid be repre- 
sented by -^q 2 >0, it is easy to understand the behaviour of these three oxides with 
the alkalies. Thus, by the action of nitrous acid on caustic potash, we obtain nitrate 
of potash -ktq I 0, whilst nitric acid gives nitrate of potash, -vtq I 0, and nitric 
peroxide gives a mixture of both salts. 



OHLOKINE. 

Cl = 35-5 parts by weight = 1vol. 35-5 grs. = 467 cub. in. at 60° F. and 30" Bar., 
35-5 grms. = 11-2 litres at 0° C. and 760 mm. Bar. 

101. This element is never found in the uncombined state, but is very 
abundant in the mineral world in the forms of chloride of sodium (com- 
mon salt) and chloride of potassium. In these forms also it is an impor- 
tant constituent of the fluids of the animal body, but as it is not found 
in sufficient proportion in vegetable food, or in the solid parts of animal 
food, a quantity of salt must be added to these in order to form a whole- 
some diet. Chloride of sodium is indispensable as a raw material for 
several of the most useful arts, such as the manufactures of soap and glass, 
bleaching, &c, in fact, it is the source of three of the most generally 
useful chemical products, viz., chlorine, hydrochloric acid, and soda. 

About the middle of the seventeenth century, a German chemist, named 
Glauber, distilled some common salt with sulphuric acid, and obtained a 
strongly acid liquid to which he gave the name muriatic acid (from muria, 
brine) and which was proved to be identical with the acid long known to 



144 



PREPARATION OF CHLORINE. 



the alchemists as spirit of salt The saline mass which was left after the 
experiment was then termed Glauber's salt, but afterwards received its 
present name of sulphate of soda. 

It was undoubtedly a natural inference from this experiment that com- 
mon salt was composed of muriatic acid and soda, and that the sulphuric 
acid had a greater attraction for the soda than the muriatic acid, which 
was therefore displaced by it. In accordance with this view, common 
salt was called muriate of soda, without further question, until the year 
1810, when the experiments of Davy proved that it was really composed 
of the two elementary substances, chlorine and sodium, and must there- 
fore be styled, as it now is, chloride of sodium, and represented by the 
formula TsTaCl. It was further shown by Davy, that the muriatic acid 
was really composed of chlorine and hydrogen, and that it was, in fact, 
chloride of sodium (NaCl) in which the sodium had been displaced by 
hydrogen (HC1). 

Preparation of chlorine. — In order to extract chlorine from common 
salt, it is heated with black oxide of manganese and diluted sulphuric 
acid ; the acid decomposes the binoxide of manganese, part of the oxygen 
of which displaces the chlorine from the chloride of sodium, yielding soda 
which combines with the sulphuric acid, so that the sulphates of soda and 
manganese are left in solution, and chlorine escapes in the form of gas ; 

2Is T aCl + Mn0 2 + 2(H 2 . SCQ = Na 2 . S0 3 + MnO . S0 3 + 2H 2 + Cl 2 . 

600 grains of common salt may "be mixed with 450 grains of binoxide of manganese, 
introduced into a retort (fig 164), and a cold mixture of 1J oz. by measure of strong 
sulphuric acid with 4 oz. of water poured upon it. The retort having "been well 




Fig. 164. — Preparation of chlorine. 

shaken to wet the powder thoroughly with the acid, a very gentle heat is applied, 
and the gas collected in bottles filled with water and inverted in the pneumatic 
trough. When the bottles are filled, the stoppers, previously greased, must be 
inserted into them under water. The first bottle or two will contain the air from the 
retort, and will therefore have a paler colour than the pure chlorine afterwards col- 
lected. It is advisable to keep a jar filled with water standing ready on the shelf of 
the trough, so that any excess of chlorine may be passed into it instead of being 
allowed to escape into the air, causing serious inconvenience. The bottles of moist 
chlorine must always be preserved in the dark. Chlorine may also be conveniently 
prepared by gently heating 500 grains of binoxide of manganese with 4 oz. (measured) 
of common hydrochloric acid — 

Mn0. 2 + 4HC1 = MnClo + 2H 2 + Cl 2 . 

Either of the above methods will furnish about five pints of chlorine. 




LIQUEFACTION" OF CHLOEINE. 145 

In Weldon's process for the manufacture of chlorine, the manganese is made to act 
as a carrier of oxygen from the atmosphere to the hydrogen of the hydrochloric acid, 
setting the chlorine free. For this purpose, the chloride of manganese obtained in 
the above process is decomposed by lime ; MnCl 2 + CaO = CaCl 2 + MnO. By mixing 
the MnO with more lime, and blowing atmospheric air through the mixture, Mn0 2 
is reproduced, and may be employed for decomposing a fresh quantity of HC1. In 
Deacon's process, a mixture of air and hydrochloric acid gas is passed over heated 
fire-brick which has been soaked in solution of sulphate of copper and dried. The 
final result is expressed by the equation 2HC1 + (N 4 + 0) = H. 2 + Cl 2 + N 4 , so that 
the chlorine obtained is mixed with twice its volume of nitrogen, which is stated, how- 
ever, not to interfere seriously with its useful application. The action of the copper- 
salt has not been clearly explained, but it appears to depend upon the instability 
of the chlorides of copper under the influence of heat and oxygen. 

Properties of chlorine. — The physical and chemical properties of chlorine 
are more striking than those of any element hitherto considered. Its 
colour, whence it derives its name (xAcopo's, pale green) is bright greenish 
yellow, its odour insupportable. It is twice and a half as heavy as air 
(sp. gr. 2*47), and may be reduced to the liquid state by a pressure of only 
four atmospheres at 60° F. If a bottle of chlorine be 
held mouth downwards in water, its stopper removed, 
one-third of the chlorine decanted into a jar, and the 
rest of the gas shaken with the water in the bottle, 
the mouth of which is closed by the palm of the hand 
(fig. 165), the water will absorb twice its volume of 
chlorine, producing a vacuum in the bottle, which will 
be held firmly against the hand by atmospheric pres- 
sure. If air be then allowed to enter, and the bottle 
again shaken as long as any absorption takes place, a 
saturated solution of chlorine (chlorine water) will be obtained. By 
exposing this yellow solution to a temperature approaching 32° ¥., yellow 
crystals of hydrate of chlorine (C1.5H 2 0) are obtained, the liquid be- 
coming colourless. 

When the water in the pneumatic trough, over which chlorine is being collected, 
happens to be very cold, the gas is often so foggy as to be quite opaque, in conse- 
quence of the deposition of minute crystals of the hydrate. On standing, the gas 
becomes clear, crystals of the hydrate being deposited like hoar-frost upon the sides 
of the bottle ; the gas also becomes clear when the bottles are slightly warmed. 

The hydrate of chlorine affords a convenient source of liquid chlorine. A number 
of bottles of saturated solution of chlorine, prepared as above, are exposed on a cold 
winter's day until the hydrate has crystallised. The crystals are thrown upon a " 
filter, cooled to nearly 32°, allowed to drain, and rammed into a pretty strong tube 
closed at one end, about twelve inches long, and half an inch in diameter, previously 
cooled in ice or snow. The tube having been nearly filled with the crystals, is kept 
surrounded with snow, whilst its upper end is gradually softened in the blowpipe 
flame and drawn off so as to be strongly sealed. When this tube is immersed in 
water at 100° F., the chlorine separates from the water, and two layers of liquid are 
formed, the lower one consisting of amber -yellow liquid chlorine (sp. gr. 1'33), and 
the upper, about three times its volume, of a pale yellow aqueous solution of chlorine. 
On allowing the tube to cool again, the crystalline hydrate is reproduced, even at 
common temperatures, being more permanent under pressure. It may even be sub- 
limed in a sealed tube. 

Liquid chlorine may also be obtained in a state in which it can be preserved, by 
disengaging the chlorine in a sealed tube {as in the liquefaction of ammonia) from 
about 200 grains of bichloride of platinum previously dried at 400° F. The bichloride 
is heated with a spirit-lamp in one limb of the tube, whilst the other is immersed 
in a freezing mixture. The face and hands of the operator should be protected 
against the bursting of the tube. 

The most characteristic chemical feature of chlorine is its powerful 

K 



146 



EXPERIMENTS WITH CHLORINE. 



attraction for many other elements at the ordinary temperature. Among 
the non-metals, hydrogen, "bromine, iodine, sulphur, selenium, phosphorus, 
and arsenic, combine spontaneously with chlorine, and nearly all the metals 
"behave in the same way. 

If a piece of dry phosphorus be placed in a deflagrating spoon, and immersed in a 
bottle of chlorine (fig. 166), it will take fire spontaneously, combining with the chlo- 
rine to form terchloride of phosphorus (PC1 3 ). A 
tall glass shade may be placed over the bottle, 
which should stand in a plate containing water, 
so that the fumes may not escape into the air. 

If phosphorus be placed in a bottle of oxygen to 
which a small quantity of chlorine has been added, 
it will burst out after a minute or two into most 
brilliant combustion. 

Powdered antimony (the metal, not the sulphide), 
sprinkled into a bottle of chlorine (fig. 167), de- 
scends in a brilliant shower of white sparks, the 
antimony burning in the chlorine to form ter- 
chloride of antimony (SbCl 3 ). A little water should 
be placed at the bottom of the bottle to prevent 
Fio-. 166. ^ f rom being cracked, and the fumes should be 

restrained by a shade standing in water. 
If a flask, provided with a stop-cock (fig. 168), be filled with leaves of Dutch metal 
(an alloy of copper and zinc, resembling gold leaf), exhausted of air, and screwed on 
to a capped jar of chlorine standing over water, it will be found, on opening the 






Fig. 167- 



Fig. 168. 



stop-cocks so that the chlorine may enter the flask, that the metal burns with a red 
light, forming thick yellow fumes containing chloride of copper (CuCl 2 ) and chloride 
of zinc (ZnCljj). If gold leaf be suspended in chlorine, it will not be immediately 
attacked, but will gradually become converted into terchloride of gold (AuCl 3 ). 

102. The most important useful applications of chlorine depend upon 
its powerful chemical attraction for hydrogen. The two gases may be 
mixed without combining, if kept in the dark, but when the mixture is 
exposed to light, they combine to form hydrochloric acid gas (HC1), with 
a rapidity proportionate to the intensity of the actinic rays (or rays capable 
of inducing chemical change) in the light employed. Exposed to gas-light 
or ordinary diffused daylight, the hydrogen and chlorine combine slowly, 
but direct sunlight causes sudden combination, attended with explosion, 



SYNTHESIS OF HYDROCHLORIC ACID. 



147 



resulting from the expansion which the hydrochloric acid formed suffers 
by the heat evolved in the act of combination. The light of magnesium 
burning in air, and some other artificial lights, also cause sudden com- 
bination. 



Two pint gas-bottles should be ground so that their mouths may be fitted accu- 
rately to each other, and filled respectively with dry hydrogen and dry chlorine, both 
gases having been dried by passing through oil of vitriol, and collected, the hydrogen 
by upward, and the chlorine by downward, displacement of air. The mouths should 
be slightly greased before the bottles are filled with gas, and afterwards closed with 
glass plates. On placing the bottles together, and removing the plates so that the 
gases may come in contact (see fig. 149), the yellow colour of the chlorine will be 
permanent as long as the mixture is kept in the dark, but on exposure to daylight 
the colour will gradually disappear, the hydrochloric acid gas being colourless. If 
the bottles be now closed with glass plates, the small quantity of gas which escapes 
during the operation will be seen to fume strongly in air, a property not possessed 
either by hydrogen or chlorine, and when the necks "of the bottles are immersed in 
water and the glass plates withdrawn, the water will rapidly absorb the gas, and be 
forced into the bottles so as to fill them, with the exception of a small space occupied 
by the air accidentally admitted, showing that the hydrochloric acid gas possesses 
the joint volumes of the hydrogen and chlorine. If the water be tinged with blue 
litmus it will be strongly reddened as it enters the bottles. 

The sudden union of the gases with explosion may be safely exhibited in a Flor- 
ence flask. The flask is filled with water, which is then poured out into a measure. 
Exactly half the water is returned 
to the flask, and its level in the 
latter carefully marked with a dia- 
mond or file. The flask having been 
again filled with water, is closed with 
the thumb and inverted in the pneu- 
matic trough, so that hydrogen may 
be passed up into it to displace one- 
half of the water. A short-necked 
funnel is then inserted, under the 
water, into the neck of the flask, 
and chlorine rapidly decanted up 
from a gas-bottle (fig. 169) until the 
rest of the water has been displaced. 
The flask is now raised from the 
water and quickly closed with a cork 
(fig. 170), through which pass two 
gutta-percha -covered copper wires, 

the ends of which have been stripped and brought sufficiently near to each other 
to allow of the passage of the electric spark within the flask. The ends external to 
the flask are also stripped and 
bent into hooks for convenient 
connexion with the conducting 
wires. The flask is placed upon 
the ground, and covered with a 
wooden box to prevent the pieces 
from flying about. On connect- 
ing the copper wires with the con- 
ducting wires from an induction- 
coil or an electrical machine, it 
will be heard, on passing the spark, 
that the mixture has violently ex- 
ploded ; on raising the box it will 
be found filled with strong fumes 
of hydrochloric acid, and a heap of 
small fragments of glass will repre- 
sent the flask. 

A flask filled in the same way with the mixture of hydrogen and chlorine may be 
attached to the end of a long stick, and thrust out into the sunlight, when it explodes 
with great violence. 

To illustrate the direct combination of hydrogen and chlorine under the influ- 




Fig. 169. 




Fig. 170. 



14:8 



EXPLOSION OF CHLORINE AND HYDROGEN. 



ence of artificial light, it is better to employ the mixture of exactly equal volumes 
of the two gases obtained by decomposing hydrochloric acid by the galvanic cur- 
rent. The voltameter (A, fig. 171) is filled with concentrated hydrochloric acid, 
and its conducting wires (B) connected with the terminals of a Grove's battery 
of five or six cells. Chlorine is at once evolved at the positive pole (or that con- 
nected with the* platinum in the battery), and hydrogen at the negative pole (at- 
tached to the zinc of the battery). It is advisable to place the voltameter in a 
vessel of cold water, to prevent the hydrochloric acid from becoming too hot. The 
gas evolved during the first five minutes should be allowed to pass into a waste-jar, 

because, until the liquid becomes 
saturated with chlorine, the 
evolved gas does not contain 
exactly equal volumes of the 
constituent elements. A very 
thin glass bulb (C), about 2 
inches in diameter, blown upon 
a stout piece of tube, the ends of 
which have been drawn out to 
narrow open points (fig. 172), is 
then connected with the volta- 
meter by means of a caoutchouc 
tube. A similar caoutchouc tube 
is attached to the free end of the 
bulb. When the colour of the 
gas in the bulb (which should be shaded from sunlight) shows that it is completely 
filled, the caoutchouc tubes are well closed by nipper-taps (fig. 173), and the bulb 
detached from the voltameter. In this condition it may be kept in the dark for 
a long time without alteration or escape of gas. The mixture may be most effec- 
tively exploded by exposing it to the flash of light evolved by firing a mixture of 
nitric oxide gas with vapour of bisulphide of carbon.* For this purpose a cylinder 
may be filled with nitric oxide (page 137) over water, closed with a glass plate, 
and placed mouth upwards upon the table ; the glass plate being lifted for an 
instant, a few drops of bisulphide of carbon are poured into the cylinder, which is 
then shaken. The bulb containing the explosive mixture is suspended at some dis- 
tance from the operator, and the gas cylinder is placed within a few inches of it 




Fig. 171. 




<4= 



ff 



Fig. 173. 



Fig. 174. 



(fig. 174). On applying a light to the cylinder, the flash will cause the immediate 
explosion of the mixture in the bulb, with production of strong fumes of hydrochloric 
acid. 

If the bulb be thin, no injury will be inflicted by the pieces of glass, or the 
operator may easily protect his face by a screen. 

The attraction of chlorine for hydrogen enables it to effect the decom- 



* A mixture of equal volumes of chlorine and hydrogen may be exploded in a strong 
cylinder by the light of a piece of magnesium tape. The cylinder should be only partly 
filled with the mixture, and firmly held with its mouth only just beneath the water in the 
trough. 



ACTION OF CHLORINE UPON HYDROGEN COMPOUNDS. 



149 



position of water. The solution of chlorine in water may be preserved 
in the dark without change; but when exposed to light it loses the 
smell of chlorine, and becomes converted into weak hydrochloric acid, 
the oxygen being liberated ; H 2 + Cl 2 = 2HC1 + 0.* The decomposi- 
tion takes place much more quickly at a red heat, so that oxygen is 
obtained in abundance by passing a mixture of chlorine and steam 
through a red-hot tube. 

For this experiment a porcelain tube is employed, which is bound round with 
sheet copper to prevent it from cracking, and loosely filled with, fragments of 
broken porcelain to expose a large heated surface. This tube is gradually heated 
to redness in a charcoal furnace (fig. 175). One end of it receives the mixture 
of chlorine with steam, obtained by passing the chlorine evolved from hydrochloric 
acid and binoxide of manganese in A (p. 144), through a flask (B) of boiling water. 
The other end of the tube is connected with a bottle (C) containing solution' of potash 
to absorb any excess of chlorine and the hydrochloric acid formed ; from this bottle 
the oxygen is collected over the pneumatic trough. 




Fig. 175.— Steam decomposed by chlorine. 



Since water is decomposed by chlorine, it is not surprising that most 
other hydrogen compounds are attacked by it. Ammonia^ (XH 3 ) is acted 
upon with great violence. If a stream of ammonia gas issuing from a tube 
connected with a flask in which solution of ammonia is heated (see fig. 147) 
be passed into a bottle of chlorine, it takes fire immediately, burning 
with a peculiar flame, and yielding thick white clouds of hydrochlorate of 
ammonia; 4XH 3 + Cl 3 = 3(XH 3 .HC1) + K A piece of folded filter- 
paper dipped in strong ammonia, and immersed in a bottle of chlorine, 
will exhibit the same effect. When the chlorine is allowed to act upon 
hydrochlorate of ammonia, its operation is less violent, and one of the 
most explosive substances is produced, which was formerly believed to be 
a chloride of nitrogen, but is probably a compound formed by the removal 
of a part of the hydrogen from ammonia, and the introduction of chlorine 
in its stead. 

* A portion of this oxygen combines with chlorine, producing hypochlorous acid, and, 
as recently stated, perchloric acid. 



150 BLEACHING BY CHLORINE. 

Many of the compounds of hydrogen with carbon are also decomposed 
with violence by chlorine. When a piece of folded filter-paper is dipped 
into oil of turpentine (C 10 H lf( ), and afterwards into a bottle of chlorine, it 
bursts into a red flame, liberating voluminous clouds of carbon and hydro- 
chloric acid. Acetylene (C 2 H 2 ) was found to explode spontaneously with 
chlorine when exposed to light (page 91). The striking decomposition of 
olefiant gas (C 2 H 4 ) by chlorine on the approach of a flame has already 
been noticed (page 93). When a lighted taper is immersed in chlorine, it 
continues to burn, but with a small red flame, the hydrogen only of the 
wax combining with the chlorine, whilst the carbon separates in black 
smoke, mixed with the hydrochloric fumes. When chlorine is brought 
in contact with the flame of a spirit-lamp, it renders the flame luminous 
by causing the separation of solid particles of carbon (page 100). It has 
been seen, in the case of olefiant gas, that chlorine sometimes combines 
directly with the hydrocarbons. 

When marsh-gas (CH 4 ) is diluted with an equal bulk of carbonic acid , 
to prevent violent action, and four volumes of chlorine added for each 
volume of marsh-gas, an oily liquid is gradually formed under the 
influence of daylight. This oily liquid is a mixture of chloroform and 
bichloride of carbon, the production of which is explained by the follow- 
ing equations : — 

CH 4 + Cl ( . = 3HC1 + CHC1 3 (Chloroform). 

CH 4 + Cl 8 - 4HC1 + CC1 4 (Tetrachloride of carbon). 

It is evident from these equations that chlorine is capable, not only of 
removing hydrogen from a compound, but also of taking its place, 
atom for atom — a mode of action which gives rise to a very large number 
of chlorinated products from, organic substances. 

The attraction of chlorine for hydrogen enables the moist gas to act as 
an oxidising agent. Thus, if marsh-gas and chlorine be mixed in the 
presence of water, and exposed to daylight, the water is decomposed, its 
hydrogen combining with the chlorine, and its oxygen with the carbon 
of the marsh-gas ; CH 4 + 2H 2 + Cl 8 = C0 2 + 8HC1. 

103. The powerful bleaching effect of chlorine upon organic colouring 
matters is now easily understood. If a solution of chlorine in water be 
poured into solution of indigo (sulphindigoiic acid) the blue colour of the 
indigo is discharged, and gives place to a comparatively light yellow 
colour. The presence of water is essential to the bleaching of indigo by 
chlorine, the dry gas not affecting the colour of dry indigo. The indigo 
is first oxidised at the expense of the water and converted into isatine, 
which is then acted upon by the chlorine and converted into chlor isatine, 
having a brownish yellow colour — 

C 8 H 5 NO {Indigo) 4- H 2 + 0\ = C 8 H 5 N0 2 (Isatine) + 2HC1 
CzH-sNO, (Isatine) + Cl 2 - C 8 H 4 C1N0. 2 + HC1 . 

^Nearly all vegetable and animal colouring matters contain carbon, hydro - 
gen, nitrogen, and oxygen, and are converted by moist chlorine into pro- 
ducts of oxidation or chlorination which happen to be colourless, or 
nearly so. 

That dry chlorine will not bleach, may be shown by shaking some oil of vitriol in 



CHLOTtlDE OF LIME. 



151 




a bottle of the gas, and allowing it to stand for an hour or two, so that the acid may 
remove the whole of the moisture. If a piece of crimson paper be dried at a moderate 
heat and suspended in the bottle while warm, it will remain 
unbleached for hours ; but a similar piece of paper sus- 
pended in a bottle of moist chlorine will be bleached almost 
immediately. If characters be written on crimson paper 
with a wet brush, and the paper placed in a jar beside a 
bottle of chlorine (fig. 176), it will be found, on removing 
the stopper, that white characters soon make their appear- 
ance on the red ground. 

If a collection of coloured linen or cotton fabrics, or 
of artificial flowers, be exposed to the action of moist 
chlorine gas or of chlorine water, those which are dyed 
with organic colouring matters will be bleached at once, 
whilst the mineral colours will for the most part 
remain unaltered. Green leaves, immersed in chlorine, 
ac quire a rich autumnal brown tint, and are eventually 
bleached. All flowers are very readily bleached by this 
g as - - Fig. 176. 

Chlorine is very extensively employed for bleach- 
ing linen and cotton, the gas acting npon the colouring matter without 
affecting the fibre, but silk and wool present much, less resistance to 
chemical action, and would be much injured by chlorine, so that they 
are always bleached by sulphurous acid. 

Neither chlorine itself nor its solution in water can be very conveniently 
employed for bleaching on the large scale, on account of the irritating 
effect of the gas, so that it is usual to employ it in the form of chloride of 
lime, from which it can be easily liberated as it is wanted. 

104. Chloride of lime or bleaching powder is prepared by passing 
chlorine gas into boxes of lead or stone in which a quantity of slaked 
lime is spread out upon shelves. The lime absorbs nearly half its weight 
of chlorine, and forms a white powder which has a very peculiar 
smell, somewhat different from that of chlorine. The chloride of lime 
thus produced appears to consist of a mixture of hypochlorite of lime 
(CaO.Cl 2 0) with oxij chloride of calcium (CaCl 2 .2CaO), the action 
of chlorine upon hydrate of lime being represented by the following 
equation : — 



4(CaO . H 2 0) 

Hydrate of lime. 



+ CI 



(CaO.Cl 2 + CaCl 2 .2CaO) + 

Chloride of lime. 



m. 2 o 



When the chloride of lime is treated with water, the hypochlorite of lime 
(CaO.Cl 2 0) aud chloride of calcium (CaCl 2 ) are dissolved, whilst hydrate 
of lime is left. If this solution be added to blue litmus, it will be found 
to exert little bleaching action, but on adding a little acid (sulphuric, for 
example), the blue colour will be discharged, the acid setting free the 
chlorine, which acts upon the colouring matter. 



(CaO.Cl 2 + CaCl 2 ) + 2(H 2 O.S0 3 ) = 2(CaO.S0 3 ) 

Solution of Chloride of lime. 



2H 2 



+ CL 



Even carbonic acid will develope the bleaching property of chloride of 
lime, so that the above mixture may be decolorised by breathing into it 
through, a glass tube. 

When chloride of lime is used for bleaching on the large scale, the stuff 
to be bleached is first thoroughly cleansed from any grease or weaver's dress- 
ing, by boiling it in lime-water and in a weak solution of soda, and is then 



1.52 DISINFECTION BY CHLORINE. 

immersed in a weak solution of the chloride of lime. This by itself, how- 
ever, exerts very little action upon the natural colouring matter of the 
fibre, and the stuff is therefore next immersed in very dilute sulphuric 
acid, when the colouring matter is so far altered as to become soluble in 
the alkaline solution in which it is next immersed, and a repetition of 
these processes, followed up by a thorough rinsing, generally perfects the 
bleaching. 

The property possessed by acids of liberating chlorine from the chloride 
of lime is applied in calico-printing to the production of white patterns 
upon a red ground. The stuff having been dyed with Turkey red, the 
pattern is imprinted upon it with a discharge consisting of an acid (tar- 
taric, phosphoric, or arsenic) thickened with gum. On passing the fabric 
through a bath of weak chloride of lime, the colour is discharged only at 
those parts to which the acid has been applied, and where, consequently, 
chlorine is liberated. 

The explanation above given of the bleaching effect of chlorine may 
probably be applied also to its so-called disinfecting properties. The 
atmosphere, in particular localities, is occasionally contaminated with 
poisonous substances, some of which are known only by their injurious 
effects upon the health, their quantity being so small that they do not 
appear in the results of the analysis of such air. Since, however, these 
substances appear to be acted upon by the same agents which are usually 
found to decompose organic compounds, they are commonly believed to 
be bodies of this class, and chlorine has been very commonly employed to 
combat these insidious enemies to health, since Guyton de Morveau, in 
the latter part of the last century, made use of it to destroy the odour 
arising from the bodies interred in the vaults beneath the cathedral of 
Dijon. 

Among the offensive and unhealthy products of putrefaction of animal 
and vegetable matter, sulphuretted hydrogen, ammonia, and bodies simi- 
larly constituted, are found. That chlorine breaks up these hydrogen 
compounds is well known, and hence its great value for removing the 
unwholesome properties of the air in badly drained houses, &c. 

Chloride of lime is one of the most convenient forms in which to apply 
chlorine for the purposes of fumigating and disinfecting. If a cloth 
saturated with the solution be suspended in the air, the carbonic acid in 
the latter causes a slow evolution of hypochlorous acid, which is even a 
more powerful disinfectant than chlorine itself. In extreme cases, where 
a rapid evolution of chlorine is required, the bleaching powder is placed 
in a plate, and diluted sulphuric acid is poured over it, or the powder may 
be mixed with half its weight of powdered alum in a plate, when a pretty 
rapid and regular escape of chlorine will ensue. 

105. The discovery of chlorine and the discussions which ensued with 
respect to its real nature, contributed very largely to the advancement of 
chemical science. About the year 1770, the Swedish chemist Scheele (who 
afterwards discovered oxygen), first obtained chlorine by heating man- 
ganese ore with muriatic acid. 

The construction which Scheele put upon the result of this experiment 
was one which was consistent with the chemistry of that date. He sup- 
posed the muriatic acid to have been deprived of phlogiston, and hence 
chlorine was termed by him dephlogisiicated muriatic acid. This phlo- 
giston had long been a subject of contention among philosophers,- having 



PREPARATION OF HYDROCHLORIC ACID. 



153 



been originally assumed to exist in combination with, all combustible 
bodies, and to be separated from them during their combustion. To- 
wards the decline of the phlogistic theory, attempts were made to prove 
the identity of this imaginary substance with hydrogen, which shows 
how. very nearly Scheele's reasoning approached to the truth, even with 
the very imperfect light which he then possessed. Berthollet's move- 
ment was retrograde when, ten years afterwards, he styled chlorine oxy- 
genised muriatic or oxymuriatic acid, but the experiments of Gay-Lussac 
and Thenard, and more particularly those of Davy in 1811, proved de- 
cisively that hydrochloric acid was composed of chlorine and hydrogen, 
and that the effect of the black oxide of manganese in Scheele's experi- 
ment was to remove the hydrogen in the form of water, thus setting the 
chlorine at liberty. 



Hydrochloric Acid. 

HC1 = 36-5 parts by weight = 2 vols. 

106. This acid is found in nature among the gases emanating from 
active volcanoes, and occasionally in the spring and river waters of vol- 
canic districts. For use it is always prepared artificially by the action 
of sulphuric acid upon common salt — 



2NaCl + H 2 

Common salt. 



SO, 



2HC1 



tfa,0 . SO, 

Sulphate of soda. 



the sodium of the common salt 
changing places with the hydro- 
gen of the sulphuric acid. 

300 grains of common salt (pre- 
viously dried in an oven) are intro- 
duced into a dry Florence flask (fig. 
177), to which has been fitted, by 
means of a perforated cork, a tube 
bent twice at right angles to allow 
the gas to be collected by downward 
displacement. Six fluid drachms of 
strong sulphuric acid are poured 
upon the salt, and the cork having 
been inserted, the flask is very 
gently heated in order to promote 
the disengagement of the hydro- 
chloric acid gas, which is collected 
in a perfectly dry bottle, the mouth 
of which, when full, may be covered 
with a glass plate smeared with a little 
be closed with a perforated card. 

Common salt in powder sometimes froths to a very inconvenient extent with sul- 
phuric acid ; it is therefore often preferable to employ fragments of fused salt, pre- 
pared by fusing the common salt in a clay crucible, and pouring on to a clean dry 
stone. 

A more regular supply of hydrochloric acid gas is obtained from lj oz. of sal-am- 
moniac in lumps, and l£ oz. (measured) of sulphuric acid. 

The bottle will be known to be filled with gas by the abundant escape 
of the dense fumes which hydrochloric acid gas, itself transparent, pro- 
duces by condensing the moisture of the air ; for since the gas is much 
heavier than air (sp. gr. 1-247), it will not escape in any quantity from 




Fig. 177. — Preparation of hydrochloric acid gas. 
grease. While being filled, the bottle may 



154 



HYDROCHLORIC OR MURIATIC ACID. 



tlie bottle until the latter is full. The odour of the gas is very suffocat- 
ing, but not nearly so irritating as that of chlorine. 

The powerful attraction for water is one of 
f Ik the most important properties of hydrochloric 

acid gas. 

If a jar of hydrochloric acid gas be closed with a 
glass plate and inverted under water, it will be found, 
on removing the plate, that the gas is absorbed with 
great rapidity, the water being forced up into the 
bottle by the pressure of the external air in propor- 
tion as the gas is absorbed. 

A Florence flask is more convenient than a gas 
bottle for this experiment. It must be perfectly dry, 
and thoroughly well filled with the gas, which may be 
allowed to escape abundantly from the mouth. The 
tube delivering the hydrochloric acid gas must be 
slowly withdrawn, so that the vacancy may be filled 
The flask is then closed with the thumb, and opened under 
The experiment may also be made 




Fig. 178. 



by gas and not by air. 

water, which will enter it with great violence. 

as in the case of ammonia (fig. 178, see page 121). 

The liquid hydrochloric, or muriatic acid of commerce, is a solution of 
the gas in water, and may be recognised by the grey fumes, with the 
peculiar odour of the acid, which it evolves when exposed to the air. One 
pint of water at a temperature of 40° F. is capable of absorbing 480 pints 
of hydrochloric acid gas, forming 1£ pint of the solution, having the 
specific gravity 1*21. The strength of the acid purchased in commerce is 
usually inferred from the specific gravity, by reference to tables indi- 
cating the weight of hydrochloric acid contained in solutions of different 
specific gravities. The strongest hydrochloric acid (sp. gr. 1*21) contains 
43 per cent, by weight of the gas. The common acid has usually a bright 
yellow colour, due to the accidental presence of a little perchloride of iron 
(Fe 2 Cl 6 ), and not unfrequently smells of chlorine. 

This acid is produced in enormous quantities in the alkali works, where 
common salt is decomposed by sulphuric acid in order to convert it into 
sulphate of soda, as a preliminary step to the production of carbonate of 
soda. The alkali manufacturer is compelled to condense the gas, for it 
is found to wither up the vegetation in the neighbourhood. For this pur- 
pose the hydrochloric acid gas is 
drawn up from the furnace 

through vertical cylinders filled 
with coke, over which streams of 
water are made to trickle. The 
water absorbs the acid, and is 
drawn off from below. 

In preparing a pure solution of the acid 
for chemical use on a small scale, the gas 
prepared as above may be passed into a 
small bottle containing a very little 
water to wash the gas, or remove any 
sulphate of soda which may splash over, 
and then into a 'bottle about two-thirds 
filled with distilled water, the tube de- 
livering the gas passing only about ^ 
inch below the surface, so that the* 
heavy solution of hydrochloric acid may 
be presented to the gas (fig. 179). For 
rdinary use, an acid of suitable strength is obtained by passing the gas from 6 




Fig. 179. — Preparation of solutiun of hydro- 
chloric acid. 

fall to the bottom, and fresh water may 



ACTION OF HYDROCHLORIC ACID ON METALS. 



155 



ounces of common salt and 10 ounces of sulphuric acid into 7 (measured) ounces 
of water until its bulk lias increased to 8 ounces. The bottle containing the water 
should be surrounded with cold water, since the absorption of hydrochloric acid by 
water is attended with evolution of heat. 

When the concentrated solution of hydrochloric acid is heated in a 
retort, it evolves abundance of hydrochloric acid gas, rendering it pro- 
bable that it is not a true chemical compound of water with the acid. 
The evolution of gas ceases when the remaining liquid contains 20 per 
cent, of acid (and has a sp. gr. of 1*10). If a weaker acid than this be 
heated, it loses water until it has attained this strength, when it distils 
unchanged.* 

The concentrated solution forms a very convenient source from which to procure 
the gas. It may be heated in a flask, and the gas dried by passing through a bottle 
filled with fragments of pumice-stone wetted with concentrated sulphuric acid, being 
collected over the mercurial trough (fig. 180). 




Fig. 180. 

The avidity with which water absorbs hydrochloric acid is the more 
remarkable, because this gas can be liquefied only under a very high 
pressure, amounting at the ordinary temperature to about 40 atmospheres. 

The liquefied hydrochloric acid has comparatively little action even 
upon those metals which decompose its aqueous solution with great 
violence ; quick-lime is unaffected by it, and solid litmus dissolves in it 
with a faint purple colour, instead of the bright red imparted by the 
aqueous hydrochloric acid. Dry hydrochloric acid gas is not absorbed by 
carbonate of lime. (These facts answer the objection that anhydrous sul- 
phuric acid (S0 3 ) cannot be considered an acid, because it has none of the 
powerful acid characters of oil of vitriol, since it cannot be doubted that 
hydrochloric acid is, in a chemical sense, an acid in its anhydrous state, 
though it manifests its acid properties only when water is present.) 

The injurious action of hydrochloric acid gas upon growing plants is 
probably connected with its attraction for water. If a spray of fresh 
leaves is placed in a bottle of hydrochloric acid, it becomes at once brown 
and shrivelled. 

107. Action of hydrochloric acid upon metals. — Those metals which 
have the strongest attraction for oxygen will also generally have the 
strongest attraction for chlorine, so that in respect to their capability of 
decomposing hydrochloric acid, they may be ranked in pretty nearly the 

* The proportion of acid thus retained by the water varies directly with the atmospheric 
pressure to which it is exposed dining the distillation. 



156 ACTION OF HYDROCHLORIC ACID ON METALLLIC OXIDES. 

same order as in their action upon water (p. 10). Since, however, the 
attraction of chlorine for the metals is generally superior to that of oxygen, 
the metals are more easily acted upon by hydrochloric acid than by water, 
the metal taking the place of the hydrogen, and a chloride of the metal 
being formed. 

Even silver, which does not decompose water at any temperature, is 
dissolved, though very slowly, by boiling concentrated hydrochloric acid, 
the chloride of silver formed being soluble in the strong acid, though it 
may be precipitated by adding water. 

Gold and platinum, however, are not attacked by hydrochloric acid, but 
if a little free chlorine be present, it converts them into chlorides. 

Iron and zinc decompose the acid very rapidly in the cold, forming 
chlorides of iron and zinc, and liberating hydrogen — 

Fe + 2HC1 = FeCl 2 + H 2 . 

When potassium or sodium is exposed to hydrochloric acid gas, it im- 
mediately becomes coated with a white crust of chloride, which partly 
protects the metal from the action of the gas, but when these metals are 
heated to fusion in hydrochloric acid gas, they burn vividly — 

Na + HC1 = NaCl + H. 

The composition of hydrochloric acid may be exhibited by confining a 
measured volume of the gas over mercury (see fig. 83, page 80), and passing 
up a freshly cut pellet of sodium. On gently agitating the tube, the gas 
diminishes in volume, and after a time will have contracted to one-half, 
and will be found to have all the properties of hydrogen. This result 
confirms that obtained by synthesis, as described above, that two volumes 
of hydrochloric acid contain one volume of hydrogen and one volume of 
chlorine. 

The electrolysis of hydrochloric acid is exhibited in the V-tube represented in fig. 
181, where the platinum plate p in the closed limb o is connected 
with a platinum wire sealed into the glass ; the other limb, h, 
is open. If the closed limb be entirely filled with strong hydro- 
chloric acid, and connected with the negative pole of a battery 
composed of five or six Grove's or Bunsen's cells, the positive pole 
being connected with h, hydrogen will rapidly collect in the 
closed limb, whilst the odour of chlorine will be perceived in the 
open limb. As soon as the liquid fills the open limb, the wire h 
is withdrawn, this limb closed with the thumb, and the hydrogen 
transferred to it by inclining the tube. After testing the hydro- 
gen with a match, the poles of the battery may be reversed, 
when the chlorine will collect as gas in the closed limb as soon 
as the hydrochloric acid has become saturated with it. 

108. — Action of hydrochloric acid upon metallic 
oxides. — As a general rule it may be stated, that when 
hydrochloric acid acts upon the oxide of a metal, the 
results are water and a chloride of the metal, in which 
each atom of oxygen in the oxide has been displaced 
Fig. 181. hy two atoms of chlorine. 

Thus, oxide of silver acted on by hydrochloric acid 
gives water and chloride of silver ; Ag 2 + 2HC1 = H 2 + 2AgCl . 
Suboxide of copper (cuprous oxide) yields water and subchloride of 
copper (cuprous chloride) ; Cu 2 + 2HC1 = H 2 + Cu 2 Cl 2 . 

Sesquioxide of iron gives water and perchloride (sesquichloride) of 
iron ; Fe 2 3 + 6HC1 = 3H 2 + Fe 2 Cl 6 . 




DOCTRINE OF ATOMICITY. 157 

With, binoxide of tin, water and tetrachloride (bichloride) of tin are 
obtained; Sn0 2 + 4HC1 = 2H 2 + SnCl 4 . 

Oxide of antimony is converted into water and terchloride of antimony ; 
Sb 2 3 + 6HC1 = 3H 2 + 2SbCl 3 . 

In cases where the corresponding chloride does not exist, oris not stable 
under the conditions of the experiment, a chloride is formed containing 
less chlorine than is equivalent to the oxygen in the oxide, and the bal- 
ance is evolved in the free state. Thus, when sesquioxide and binoxide 
of manganese are heated with hydrochloric acid — 

Mn 2 3 + 6HC1 - 3H 2 + 2MnCl 2 + Cl 2 
Mn0 2 + 4HC1 - 2H 2 + MnCl 2 + Cl 2 

Chromic acid, a chloride corresponding to which is not known to exist, 
when heated with hydrochloric acid, yields chromic chloride and 
chlorine; 2Cr0 3 + 12HC1 = 6H 2 + Cr 2 Cl 6 + Cl 6 . 

Every metallic oxide containing one atom of oxygen has a correspond- 
ing chloride of a stable character, but the higher oxides less frequently 
form corresponding chlorides endowed with any stability. 

109. Molecular weight of hydrochloric acid. — It is ascertained by ex- 
periment that 36*5 grains of hydrochloric acid are required to neutralise 
one molecule (56 grains) of caustic potash. The number 36*5, therefore, 
represents the molecular weight of hydrochloric acid, and this receives 
confirmation from the circumstance that 36*5 parts by weight of hydro- 
chloric acid gas occupy twice the volume of 1 part by weight of hydro- 
gen (see page 36). 

110. Types of atomic formulas ; atomicity. — On examining the com- 
position by volume of hydrochloric acid, water, ammonia, and marsh-gas, 
it is seen that equal volumes of these compounds, measured in the gaseous 
state at the same temperature and pressure, contain respectively, 1, 2, 3, 
and 4 volumes of hydrogen. 

Thus 2 volumes of hydrochloric acid gas contain, 1 volume of chlorine and 

1 volume of hydrogen. 
2 volumes of watery vapour contain 1 volume of oxygen and 2 

volumes of hydrogen. 
2 volumes of ammonia contain 1 volume of nitrogen and 3 volumes 

of hydrogen. 
2 volumes of marsh-gas contain 1 volume (?) of imaginary carbon 

vapour and 4 volumes of hydrogen. 

In the case of the marsh-gas, it has been already explained that the 
volume occupied by a given weight of carbon vapour cannot be ascer- 
tained by experiment, but there are reasons to justify the assumption that 
12 parts by weight of carbon vapour would occupy the same volume as 
1 part by weight of hydrogen. In the other cases, the above statements 
exhibit the direct results of experiments previously described. 

If it be allowed that one atom of each element occupies one volume, 
then hydrochloric acid, water, ammonia, and marsh-gas will contain, for 
one atom of chlorine, oxygen, nitrogen, and carbon, respectively, 1, 2, 3, 
and 4 atoms of hydrogen, or, taking the symbol for each element to re- 
present one atom — 



158 ATOMICITIES OF THE ELEMENTS. 

Vols. Weights. 

Hydrochloric acid = C1H = HC1 = 2 = 36 T 5 

Water = HH = H 2 = 2 = 18 

Ammonia = N HHH = H 3 IS T =2 = 17 

Marsh-gas = C HHHH= H 4 C = 2 = 16 

Since, on. the atomic theory, hydrogen is accepted as the unit of atomic 
weight and volume, it appears reasonable to fix upon it as representing 
the unit of combining power, and to classify the elements according to the 
tendency of their atoms to imitate the combining power of one or more 
atoms of hydrogen. 

By the atomicity or quantivalence of an element is meant the number 
expressing the hydrogen-atoms to which one atom (or volume) of that 
element is usually equivalent. 

Thus, the atomicity of chlorine is = 1, for one volume (or atom) of this 
element not only combines with, and neutralises the properties of, 
one atom (or volume) of hydrogen, but is capable of representing, or 
occupying the place of, one atom of hydrogen in its compounds (see 
page 150). 

The atomicity of oxygen is = 2, since one volume (or atom) of oxygen 
combines with, and neutralises, two atoms (or volumes) of hydrogen in 
water, and is generally capable of occupying the place of two atoms of 
hydrogen in the compounds of that element. 

The atomicity of nitrogen is = 3, for one volume (or atom) of nitrogen 
neutralises the properties of three atoms (or volumes) of hydrogen in 
ammonia, and is often found to occupy the place of three atoms of hydro- 
gen in its compounds. 

The atomicity of carbon is = 4, for one volume (or atom) of imaginary 
carbon vapour is combined, in marsh-gas, with four atoms (or volumes) of 
hydrogen, and in its compounds with other elements, one atom of carbon 
is usually found representing four atoms of hydrogen. 

Since hydrochloric acid, water, ammonia, and marsh-gas are the most 
conspicuous members of large classes of chemical compounds, they are 
often referred to as types, and the elements, chlorine, oxygen, nitrogen, 
and carbon, are taken as 'the representatives of the various classes into 
which the elements are divided according to their atomicities. 

Chlorine is the type of one-atom elements (technically called mon- 
atomic, uni-equivalent, monad elements), the atomic weights of which are 
represented by the same numbers as their equivalent weights. 

Oxygen is the type of two-atom elements (di-atomic, bi-equivalent, dyad 
elements), of which the number representing the equivalent weight is 
half of that which represents the atomic weight. 

Equivalent of oxygen = 8. 
Atom of oxygen = 16. 

Mtrogen is the type of three-atom elements (tri-aiomic, ter-equivalent, 
triad elements), of which the number representing the equivalent weight 
is commonly taken as identical with that which represents the atomic 
weight, though if the equivalentic system were rigorously carried out, the 
equivalent should be one-third of the atomic weight. 

Carbon is the type of four-atom elements (tetratomic, quadrequivalent, 
tetrad elements), of which the number representing the equivalent weight 



GRAPHICAL REPRESENTATION OF ATOMS. 159 

ought to be one-fourth of that which expresses the atomic weight, whereas 
it is usually represented as half that number. 

Equivalent of carbon = 6. 
Atom of carbon = 12. 

Such anomalies as these are unavoidable during the present transitional 
period through which chemistry appears to be passing towards the ulti- 
mate adoption of atomic (or molecular) formula? in the place of equivalent 
formulae, a change which offers dazzling prospects of advantage in specu- 
lative chemistry, but will probably be of less service in practice than the 
preservation of equivalent formulas, so corrected as to remove the anomalies 
presented in some few cases. 

The experience of the last few years seems to warrant the belief that it 
will be long before experiment (the only possible final resort for the 
chemist) has so far removed the exceptions to the atomic formulae which 
are presented, in some cases, by the gaseous volumes and specific heats of 
the elements, that these formulae can be said to present us with so true a 
record of the actual results of experiment as to console us for the loss of 
the greater simplicity and practical utility of the equivalent formulae. 

It is remarkable that the four elements, hydrogen, oxygen, nitrogen, 
and carbon, which compose the chief part of living matter, are respectively 
monatomic, diatomic, triatomic, and tetratomic elements. 

In speculations relating to the atomic structure of compounds, it is 
now usual to represent graphically the atomicity of each element ; thus 
a monatomic element, like hydrogen, is represented as affording one point 
of attachment, which may be indicated by writing the symbol H — ; a 
diatomic element, like oxygen, affords two points of attachment, as shown 
by writing its atomic symbol — — ; accordingly, to form water, the dia- 
tomic oxygen attaches to itself two atoms of hydrogen, as represented by 
the molecular formula H — — H, whereas in the peroxide of hydrogen 
(H 2 2 ) the second atom of oxygen is only held by one point of attach- 
ment, so that the graphic expression H — — H — — accounts at once 
for its tendency to decompose into water and free oxygen. A triatomic 

element, such as nitrogen, has three points of attachment \]ST — , and 

IT* 

thus in ammonia, attaches to itself three atoms of hydrogen NX — H. 

The tetratomic element, carbon, affords four points of attachment ^>C<Q 
and thus marsh-gas (CH 4 ) is represented by ^>C<Q , and carbonic acid 
(CO,) by 0<>C<()>0. 

Compounds of Chlorine with Oxygen. 

111. It is worthy of notice that whilst chlorine and hydrogen so readily 
unite, there is no method by which chlorine can be made to combine in a 
direct manner with oxygen, all the compounds of these elements having 
been hitherto obtained only by indirect processes. An excellent illustra- 
tion is thus afforded of the fact, that the more closely substances resemble 
each other in their chemical relations, the less will be their tendency to 



160 HYPOGHLOEOUS ACID. 

combine, for chlorine and oxygen are both highly electronegative bodies, 
and therefore, having both a powerful attraction for the electropositive 
hydrogen, their attraction for each other is of a very low order. 

112. Hypochlorous acid (C1. 2 0) is of some practical interest as one of 
the constituents of chloride of lime, chloride of soda, and other bleaching 
compounds. It is prepared by passing dry chlorine gas over dry precipi- 
tated oxide of mercury, and condensing the product in a tube surrounded 
with a mixture of ice and salt — 

HgO {oxide of mercury) + Cl 4 = HgCI 2 (bichloride of mercury) -f- C1 2 . 

The hypochlorous acid is thus obtained as a deep red liquid, which boils 
at 19° P., evolving a yellow vapour thrice as heavy as air, and having a 
very powerful and peculiar odour. This vapour is remarkably explosive, 
the heat of the hand having been known to cause its separation into its 
constituents, when two volumes of the vapour yield two volumes of 
chlorine and one volume of oxygen. As might be expected, most sub- 
stances which have any attraction for oxygen or chlorine will decompose 
the gas, sometimes with explosive violence. Even hydrochloric acid de- 
composes it ; one volume of hypochlorous acid gas is entirely decomposed 
by two volumes of hydrochloric acid, yielding water and chlorine — 

C1 2 + 2HC1 = H 2 + Cl 4 . 

Hypochlorous acid is a powerful bleaching agent, both its chlorine and 
oxygen acting upon the colouring matter in the manner explained at 
page 150. 

Hypochlorous acid is absorbed in large quantity by water. The solu- 
tion may be very readily prepared by shaking the red oxide of mercury 
with water in a, bottle of chlorine as long as the gas is absorbed. The 
greater part of the chloride of mercury which is produced combines with 
the excess of oxide of mercury to form a brown insoluble oxychloride, 
whilst the hypochlorous acid and a little chloride of mercury remain in 
solution. This solution is a most powerful oxidising and bleaching agent ; 
it erases writing ink immediately, and does not corrode the paper if it be 
carefully washed. Printing ink, which contains lamp-black and grease, 
is not bleached by hypochlorous acid, so that this solution is very useful 
for removing ink stains from books, engravings, &c. 

The action of some metals and their oxides upon solution of hypo- 
chlorous acid is instructive. Iron seizes upon the oxygen, whilst the. 
chlorine is liberated ; copper takes both the oxygen and chlorine, whilst 
silver combines with the chlorine and liberates oxygen. Oxide of lead 
(PbO) removes the oxygen, becoming peroxide of lead (Pb0 2 ), and libe- 
rating chlorine, but oxide of silver converts the chlorine into chloride of 
silver, and liberates the oxygen ; Ag 2 + C1 2 = 2AgCl + 2 . 

The salts of hypochlorous acid, or hypochlorites, are not known in a 
pure state, but are obtained in solution by neutralising the solution of 
hypochlorous acid with bases. They are decomposed even by carbonic 
acid, with liberation of hypochlorous acid. 

When the solution of a hypochlorite is boiled, it becomes converted 
into a mixture of chloride and chlorate ; thus — 

3(K 2 0.C1 2 0) = 2(KClCg + 4KC1. 

Hypochlorite of potash. Chlorate of potash. StaSiumf 



CHLORATE OF POTASH. 161 

This change is turned to practical account in the manufacture of chlorate 
of potash. It is much hindered by the presence of an excess of alkali. 
The solution of hypochlorous acid itself, when exposed to light, is decom- 
posed into chloric acid and free chlorine — 

5C1 2 + H 2 - 2HC10 3 + Cl 8 . 

Chloride of lime (see p. 151) is the most important compound 
containing hypochlorous acid. Its formula has already been given as 
CaO.Cl 2 + CaCl 2 .2CaO + 4Aq, showing it to be a mixture of hypo- 
chlorite of lime with oxychloride of calcium. When this compound is 
distilled with a small quantity of diluted sulphuric acid, a solution of 
hypochlorous acid is obtained ; but if an excess of acid be used, the chlo- 
ride of calcium is decomposed, furnishing hydrochloric acid, which acts 
upon the hypochlorous acid, and free chlorine is the result. Alcohol, 
although capable of dissolving chloride of calcium, does not extract that 
salt from bleaching powder, because it is combined with lime ; but an 
excess of water decomposes the compound of chloride of calcium with 
lime, and dissolves the former. 

Bleaching powder is liable to decomposition when kept, its hypochlorite 
of lime evolving oxygen, and becoming converted into chloride of calcium, 
which attracts moisture greedily, and renders the bleaching powder deli- 
quescent. It has been known to shatter the glass bottle in which it was 
preserved, in consequence of the accumulation of oxygen. 

When a solution of salt of manganese or cobalt is added to solution 
of chloride of lime, a black precipitate of binoxide of manganese or sesqui- 
oxide of cobalt is obtained, the oxide of manganese or of cobalt acquiring 
additional oxygen from the hypochlorite of lime, and forming an oxide 
which is indifferent, and does not remain in combination with the acid. 
If this precipitate be boiled with an excess of solution of chloride of 
lime, it causes a rapid disengagement of oxygen in some manner that has 
not yet been clearly explained. 

Large quantities of oxygen are easily obtained by adding a few drops of 
solution of nitrate of cobalt to solution of chloride of lime, and applying a 
gentle heat. 

Hypochlorite of soda, which is very useful forremoving ink, is prepared 
in solution by decomposing solution of chloride of lime with solution of 
carbonate of soda, and separating the carbonate of lime by filtration. 
The solution is generally called " chloride of soda." 

113. Chloric acid (HC10 3 ). — This acid is appropriately studied here, 
since its compounds are usually obtained by the decomposition of the 
hypochlorites. The only compound of chloric acid which possesses any- 
great practical importance is the chlorate of potash (KC10 3 ) which is 
largely employed as a source of oxygen, as an ingredient of several explo- 
sive compositions, and in the manufacture of lucifer matches. 

Chlorate of potash. — The simplest method of obtaining this salt con- 
sists in passing an excess of chlorine rapidly into a strong solution of 
potash, when the liquid becomes hot enough to decompose the hypo- 
chlorite of potash first formed, into chloride of potassium, which remains 
in solution, and chlorate of potash, which is deposited in tabular crystals, 
the ultimate result being expressed by the equation — 

6(KHO) + Cl 6 = KCIO3 + 5KC1 + 3H 2 . 




162 PREPARATION OF CHLORATE OF POTASH. 

If carbonate of potash or a weak solution of hydrate of potash be employed, 
the liquid will require boiling after saturation with chlorine, in order to 
convert the hypochlorite into chlorate. 

The following proportions will be found convenient for the preparation of chlorate of 
potash on the small scale as a laboratory experiment. 
300 grains of carbonate of potash are dissolved, in a 
beaker, with two measured ounces of water. 600 
grains of common salt are mixed with 450 grains of 
binoxide of manganese, and very gently heated in 
a flask (fig. 182) with a mixture of 1^ ounce (mea- 
sured) of strong sulphuric acid and 4 ounces (mea- 
sured) of water, the evolved chlorine being passed 
through a rather wide bent tube into the solution 
of carbonate of potash. 

At first no action will appear to take place, 
although the solution absorbs the chlorine ; be- 
cause the first portion of that gas converts the car- 
bonate of potash into a mixture of hypochlorite of 
potash, chloride of potassium, and bicarbonate of 
potash, some crystals of which will probably be de- 

Fig. 182. P ° Sited - 

4(K 2 O.C0 2 ) + Cl 4 + 2H 2 = 2KC1 + K 2 0.C1 2 + 2(K 2 O.H 2 0.2C0 2 ) . 

On continuing to pass chlorine, these crystals will redissolve, and brisk efferves- 
cence will be caused by the expulsion of the carbonic acid from the bicarbonate of 
potash — 

2(K 2 O.H 2 0.2C0 2 ) + Cl 4 = 2KC1 + K 2 0.C1 2 + 2H 2 + 4C0 2 . 

When this effervescence has ceased, and the chlorine is no longer absorbed by the 
liquid, the change is complete, the ultimate result being represented by the 
equation — 

2(K 2 O.C0 2 ) + Cl 4 = 2KC1 + K 2 0.C1 2 + 2C0 2 . 

The solution (which often has a pink colour, due to a little permanganate 
of potash) is now poured into a dish, boiled for two or three minutes, filtered, if ne- 
cessary, from any impurities (silica, &c.,) derived from the carbonate of potash, and 
set aside to crystallise. The ebullition has converted the hypochlorite of potash into 
chlorate of potash and chloride of potassium — 

3(K 2 0.C1 2 0) = 2KC10 8 + 4KC1 . 

The latter being soluble in about three times its weight of cold water, is retained 
in the solution, whilst the chlorate of potash, which would require about sixteen 
times its weight of cold water to hold it dissolved, is deposited in brilliant rhom- 
boidal tables. These crystals may be collected on a filter, and purified from the 
adhering solution of chloride of potassium by pressure between successive portions 
of filter-paper. If they be free from chloride of potassium, their solution in water 
will not be changed by nitrate of silver, which would yield a milky precipitate of 
chloride of silver if that impurity were present. Should this be the case, the crys- 
tals must be redissolved in a small quantity of boiling water and recrystallised. 

The above processes for preparing the chlorate of potash are far from 
economical, since five-sixths of the potash are converted into chloride, 
being employed merely to furnish oxygen to convert the chlorine into 
chloric acid. In manufacturing chlorate of potash upon the large scale, a 
much cheaper material, lime, is used to furnish the oxygen, one molecule 
of carbonate of potash being mixed with six molecules of slaked lime, 
and the damp mixture saturated with chlorine. On treating the mass 
with boiling water, a solution is obtained which contains chlorate of 
potash and chloride of calcium, the latter, being very soluble, remains in 
the liquor from which the chlorate of potash crystallises on cooling. The 



DETONATING COMPOSITIONS. 



163 



ultimate result of the action of chlorine upon the mixture of carbonate of 
potash and lime is thus expressed — 

K 2 O.C0 2 + 6CaO + Cl 12 = 2KC10 3 + 5CaCl 2 + CaO.CO,. 

A still cheaper salt of potassium, the chloride, has recently been em- 
ployed with great economy as a substitute for the carbonate of potash. 
The solution of chloride of potassium is mixed with lime, and saturated 
with chlorine in close leaden tanks. The solution is filtered, evaporated 
nearly to dryness, and redissolved in hot water, when the chlorate of 
potash crystallises out on cooling. The chloride of calcium is precipi- 
tated by carbonate of soda to obtain precipitated chalk. 

Anhydrous chloric acid (C1 2 5 ) has never been obtained in the separate 
state ; but its hydrate (H^O.Cl^Og or HC10 3 ) may be procured by decom- 
posing a solution of chlorate of potash with hydrofluosilicic acid, when 
the potassium is deposited as an insoluble silico-fluoride, and hydrated 
chloric acid is found in the solution* — 

2KC10 3 + 2KF.SiF 4 (nydrojiuosiiicic add) = 2HC10 3 + 2KF.SiF 4 . 

On evaporating the solution at a temperature not exceeding 100° F., 
the hydrated chloric acid is obtained as a yellow liquid with a peculiar 
pungent smell. 

In its chemical characters, hydrated chloric acid bears a very strong 
resemblance to hydrated nitric acid, but is far more easily decomposed. 
It cannot even be kept unchanged for any length of time, and at tem- 
peratures above 104° F. it is decomposed into perchloric acid, chlorine, 
and oxygen — 

4(HC10 3 ) = 2HC10 4 + H 2 + Cl 2 + 3 . 

Hydrated chloric acid is one of the most powerful oxidising agents ; 
a drop of it will set fire to paper, and it oxidises phosphorus (even the 
amorphous variety) with explosive violence. 

Chlorates. — Chloric acid, like nitric, is monobasic, containing only 
one atom of hydrogen replaceable by a metal. The chlorates resemble the 
nitrates in their oxidising power, but generally act at 
lower temperatures, in consequence of the greater facility 
with which the chlorates part with their oxygen. 

A grain or two of chlorate of potash, rubbed in a mortar with 
a little sulphur, for example, detonates violently, evolving a 
powerful odour of chloride of sulphur. Chlorate of potash and 
sulphur were used in some of the first percussion caps, but being 
found to corrode the nipple of the gun, they gave place to the 
anticorrosive caps containing fulminate of mercury. 

If a little powdered chlorate of potash be mixed, on a card, 
with some black sulphide of antimony, and wrapped up in paper, 
the mixture will detonate when struck with a hammer. 

A mixture of this description is employed in the friction tubes 
used for firing cannon. These are small tubes (A, fig. 183) of sheet 
copper (for military) or of quill (for naval use), filled with gun- 
powder ; in the upper part of the tube a small copper rasp (B) 
is tightly fixed across it, and on each side of the rasp a pellet is 
placed containing 12 parts of chlorate of potash, 12 of sulphide 
of antimony, and 1 of sulphur, these ingredients being worked up 
into a paste with a solution of an ounce of shellac in a pint of 
spirit of wine . The friction tube is fixed in the vent of the gun, 
and the copper rasp quickly withdrawn by a cord in the hands of the 
gunner, when the detonating pellets explode and fire the powder. 




Fig. 183. 



* 440 grain measures of hydrofluosilicic acid of sp. 
of chlorate of potash, ' 



gr. 1078 will decompose 100 grains 




164 COLOURED FIRES. 

The earliest lucifer matches were tipped with a mixture of chlorate of potash, 
sulphide of antimony and starch, and were kindled by drawing them briskly through 
a doubled piece of sand-paper. 

At high temperatures the chlorates act violently upon combustible 
bodies. A little chlorate of potash sprinkled upon red-hot coals causes a 
very violent deflagration. If a little chlorate of pot- 
ash be melted in a deflagrating spoon, and plunged 
into a bottle or flask containing coal-gas (fig. 184), 
the salt burns with great brilliancy, its oxygen com- 
bining with the carbon and hydrogen in the gas, 
which becomes, in this case, the supporter of com- 
bustion. The flask may be conveniently filled with 
coal-gas by inverting it, and passing a flexible tube 
from the gas pipe up into it. 

Chlorate of potash is much used in the manufac- 
ture of fireworks, especially as an ingredient of 
coloured fire compositions, which generally consist 
of chlorate of potash mixed with sulphur, and with 
Fio . lg4 some metallic compound to produce the desired 

colour in the flame. They are not generally made 
of the best quality on the small scale, from want of attention to the very 
finely powdered state of the ingredients, the absence of all moisture, and 
the most intimate mixture. 

If these precautions be attended to, the following prescription will give very 
good coloured fires : — 

Red fire. — 40 grains of nitrate of strontia, thoroughly dried over a lamp, are mixed 
with 10 grains of chlorate of potash, and reduced to the finest possible powder. In 
another mortar 13 grains of sulphur are mixed with 4 grains of black sulphide of 
antimony (crude antimony). The two powders are then placed upon a sheet of 
paper, and very intimately mixed with a bone knife, avoiding any great pressure. 
A little heap of the mixture touched with a red-hot iron ought to burn with a 
uniform red name, the colour being due to the strontium. 

Blue fire. — 15 grains of chlorate of potash are mixed with 10 grains of nitrate of 
potash and 30 grains of oxide of copper, in a mortar. The finely-powdered mixture 
is transferred to a sheet of paper, and mixed, by a bone knife, with 15 grains of 
sulphur. The colour of the fire is given chiefly by the copper. 

Green fire. — 10 grains of chlorate of baryta are mixed with 10 grains of nitrate of 
baryta in a mortar, and afterwards, on paper, with 12 grains of sulphur. The barium 
is the cause of the bright green colour of the flame. 

These compositions are rather dangerous to keep, since they are liable to spon- 
taneous combustion. 

White gunpowder is a mixture of two parts of chlorate of potash with one part of 
dried yellow prussiate of potash, and one part of sugar, which explodes very easily- 
under friction or percussion. 

The decomposition of chlorate of potash by heat into oxygen and chlo- 
ride of potassium is attended with evolution of heat, unlike most cases of 
chemical decomposition, in which heat is generally absorbed. If chlorate 
of potash be heated to the point at which it begins to decompose, and a 
little peroxide of iron be thrown into it, enough heat will be evolved to 
bring the mass to a red heat, although the peroxide of iron is not oxidised. 
Experiment has shown that one part of chlorate of potash evolves, during 
decomposition, nearly 39 units of heat, or enough heat to raise 39 parts of 
water through 1° C. This anomalous evolution of heat must of course 
contribute to increase the energy of explosive mixtures containing the 
chlorate, and may be accounted for on the supposition, that the heat evolved 
by the combination of the potassium with the chlorine to form chloride of 



CHLORIC PEROXIDE. 165 

potassium exceeds that which is absorbed in effecting the chemical disin- 
tegration of the chlorate. 

114. Anhydrous perchloric acid (C1 2 7 ) is not known. The hydrated 
acid is obtained by evaporating down, at a boiling heat, the solution of 
chloric acid obtained by decomposing chlorate of potash with hydrofluo- 
silicic acid (see p. 163), when the chloric acid is decomposed into per- 
chloric acid, chlorine, and oxygen — 

4(HC10 3 ) - 2HC10 4 + H 2 + Cl 2 + 3 . 

When the greater part of the water has been boiled off, the liquid may be intro- 
duced into a retort and distilled. After the remainder of the water has passed over, 
it is followed by a heavy oily liquid which is HC10 4 .2H 2 0. If this be mixed with 
four times its volume of strong sulphuric acid and again distilled, the pure hydrated 
perchloric acid (HC10 4 ) first passes over as a yellow watery liquid. If the distillation 
be continued, the oily HC10 4 . 2H 2 distils over, and if this be mixed with the former 
and cooled, it yields silky crystals containing HC10 4 .H 2 0, which are decomposed at 
230° F. into HC10 4> which may be distilled off, and HC10 4 .2H 2 0, which is left in 
the retort — 

2(HC10 4 .H 2 0) = HC10 4 + HC10 4 .2H 2 . 

The pure hydrated perchloric acid is a colourless, very heavy liquid 
(sp. gr. 1'782), which soon becomes yellow from decomposition. It 
cannot be kept for any length of time. When heated it undergoes 
decomposition, often with explosion. In its oxidising properties it is 
more powerful than chloric acid. It burns the skin in a very serious 
manner, and sets fire to paper, charcoal, &c, with explosive violence. 
This want of stability, however, belongs only to the pure hydrate. If 
water be added to it heat is evolved, and a diluted acid of far greater per- 
manence is obtained. Diluted perchloric acid does not even bleach, but 
reddens litmus in the ordinary way. 

Perchloric acid is monobasic. The per cl dor cites are decomposed by 
heat, evolving oxygen, and leaving chlorides ; thus — 

KC10 4 (Perchlorate of potash) = KC1 + 4 . 

The perchlorate of potash is always formed in the first stage of the decom- 
position of chlorate of potash by heat — 

2(KC10 3 ) = KC10 4 + KCf + 2 . 

If a few crystals of chlorate of potash be heated in a test-tube, they first melt to 
a perfectly clear liquid, which soon evolves bubbles of oxygen. After a time the 
liquid becomes pasty, and if the contents of the tube, after cooling, be dissolved by 
boiling with water, the latter will deposit, as it cools, crystals of perchlorate of 
potash. These are readily distinguished from chlorate of potash by their not yield- 
ing a yellow gas (C10 2 ) when treated with strong sulphuric acid. The perchlorate 
of potash is remarkable as one of the least soluble of the salts of potash, requiring 
150 times its weight of cold water to dissolve it. Neither perchloric acid nor any 
of its salts is applied to any useful purpose. 

115. Chloric peroxide or peroxide of chlorine (C10 2 ) is dangerous to prepare and 
examine on account of its great instability and violently explosive character. It is 
obtained by the action of strong sulphuric acid upon chlorate of potash — 

3(KC10 3 ) + 2H 2 S0 4 = KC10 4 + 2(KHS0 4 ) + 2C10 2 + H 2 . 
Chlorate of c„i„i„™-„ a ^A Perchlorate of Bisulphate of Chloric per- 
potash. Sulphuric add. potagh< p( £ ash- oxide . 

It is a bright yellow gas, with a chlorous and somewhat aromatic smell, and sp. gr. 
2-32; condensible at —4° F. to a red, very explosive liquid. The gas is gradually 
decomposed into its elements by exposure to light, and a temperature of 140° F. 



166 CHLOEOUS ACID. 

causes it to decompose with violent explosion into a mixture of chlorine and oxygen, 
the volume of which is one-third greater than that of the compound. 

On a small scale chloric peroxide may be prepared with safety by pouring a little 
strong sulphuric acid upon one or two crystals of chlorate of potash in a test-tube 
supported in a holder. The crystals at once acquire a red colour, which gradually 
diffuses itself through the liquid, and the bright yellow gas collects in the tube. If 
heat be applied, the gas will explode, and the colour and odour of chloric peroxide 
will be exchanged for those of chlorine. If the chlorate of potash employed in this 
experiment contains chloride of potassium, explosion often takes place in the cold, 
since the hydrochloric acid evolved by the action of the acid upon that salt decom- 
poses a part of the chloric peroxide, and thus provokes the decomposition of the 
remainder. 

Chloric peroxide is easily absorbed by water, and the solution has 
powerful bleaching properties. Combustible bodies, such as sulphur and 
phosphorus, decompose the gas, as might be expected, with great violence. 
This powerful oxidising action of chloric peroxide upon combustible sub- 
stances, appears to be the cause of the property possessed by mixtures 
of such substances with chlorate of potash to inflame when touched with 
strong sulphuric acid. 

If a few crystals of chlorate of potash be thrown into a glass of water (fig. 185), 
one or two small fragments of phosphorus dropped upon them, 
and some strong sulphuric acid poured down a funnel tube to 
the bottom of the glass, the chloric peroxide will inflame the 
phosphorus with bright flashes of light and slight detonations. 

Powdered sugar, mixed with chlorate of potash, on paper, will 
burn brilliantly when touched with a glass rod dipped in strong 
sulphuric acid. Matches may be prepared which inflame when 
moistened with sulphuric acid, by dipping the ends of splinters 
of wood in melted sulphur, and when cool, tipping them with a 
mixture of 5 grains of sugar and 15 grs. of chlorate of potash 
made into a paste with 4 drops of water. "When dry they may 
be fired by dipping them into a bottle containing asbestos mois- 
tened with strong sulphuric acid. These matches, under the 
names of Eupyrion and Vesta matches, were used before the 
introduction of phosphorus into general use. The Promethean 
light was an ornamental scented paper spill, one end of which 
Fig. 185. contained a small glass bulb of sulphuric acid surrounded with 

a mixture of chlorate of potash and sugar, which inflamed when 
the end of the spill was struck or squeezed, so as to break. the bulb containing the 
sulphuric acid. The paper was waxed in order to make it inflame more easily. Per- 
cussion fuses, &c, have been often constructed upon a similar principle. 

Chloric peroxide used to be called hypochloric acid, but, like nitric 
peroxide, it appears to have no claim to be considered a true acid, since, 
in contact with the alkalies, it yields mixtures of chlorites and chlorates; 
thus — 

4C10 2 + 2K 2 = K 2 0.C1 2 3 + 2KC10 3 . 

Euclilorine, the deep yellow, dangerously explosive gas evolved by the 
action of strong hydrochloric acid upon chlorate of potash, appears to be 
a compound of anhydrous chloric and chlorous acids (2C1 2 5 .C1 2 3 ) mixed 
with free chlorine. 

116. Chlorous acid (C1 2 3 )* is another unstable and dangerously 
explosive gas, obtained by the action of a very gentle heat upon a mix- 
ture of three parts of arsenious acid, four of chlorate of potash, and sixteen 
of diluted nitric acid (sp. gr. 1*24) — 

* This gas occupies three times the volume of an atom of hydrogen, instead of twice that 
volume, as usual. 




REVIEW OF OXIDES OF CHLORINE. 



167 



2KC10 3 {Chlorate of potash) 4- 2ILN0 3 {Nitric acid) + As 2 3 {Arsenious acid) = 
2KN0 3 {Nitrate of potash) + As 2 5 {Arsenic acid) + C1 2 3 {Chlorous acid) + H 2 . 

Chlorous acid is a deep yellowish green heavy gas (sp. gr. 2 -65) which 
is absorbed by water, and decomposed even more easily than the chloric 
peroxide. It is a weak acid, its salts, the chhrites, being decomposed 
even by carbonic acid. A mixture of ice and salt does not liquefy 
chlorous acid, but an intense cold condenses it to a red liquid, of sp. gr. 
1*33, which boils at a little above the melting-point of ice, and explodes 
at a somewhat higher temperature. 

117. General review of the oxides of chlorine. — Several points of resem- 
blance will have been noticed between the series of oxides of chlorine and 
those of nitrogen, but the former are much less stable than the latter. 
Chlorous acid (C1 2 3 ), like nitrous acid (N" s 3 ), is a weak acid ; chloric 
peroxide (C10 2 or C1 2 4 ) is easily resolved by bases into chlorous and 
chloric acids, just as nitric peroxide (N0 2 or JN" 2 "0 4 ) is resolved into nitrous 
and nitric acids. The hydrated chloric acid (HC10 3 ) is a powerful oxi- 
dising agent like hydrated nitric acid (HN0 3 ), and the chlorates resemble 
the nitrates in their solubility in water and their oxidising power. The 
composition by volume of those oxides of chlorine which are known in 
the separate state, is exhibited in the following table : — 





Formula. 


Molecular 
Weight. 


Molecular 
Volume. 


By Volume. 


CI 





Hypochlorous acid . 
Chlorous acid . . . 
Chloric peroxide . . 


C1 2 

ci 2 o 3 

cio 2 


87 
119 
67-5 


2 
3 

2 


2 
2 
1 


1 
3 

2 



Some chemists refuse to regard the hypochlorites and chlorites, as com- 
posed of basic oxides united with hypochlorous and chlorous acids respec- 
tively, but consider them as derived from (hypothetical) hydrated hypo- 
chlorous acid (H 2 0.C1 2 or HCIO) and {hypothetical) hydrated chlorous 
acid (HjO.CLjOa or HC10 2 ), by the substitution of metals for the hydrogen 
contained in those compounds. Thus hypochlorite of lime (CaO.Cl 2 0) 
would become Ca(C10) 2 , chlorite of potash (K 2 0.C1 2 3 ) would be KC10 2 . 



Chlorides of Carbon. 

118. It has already been seen that chlorine has no direct attraction for 
carbon, the two elements not being known to enter into direct combina- 
tion, but several chlorides of carbon may be obtained by the action of 
chlorine upon other compounds of carbon. Thus, if Dutch liquid 
(C 2 H 4 C1 2 ), produced by the combination of olefiant gas with chlorine 
(p. 92), be acted upon with an excess of chlorine in sunlight, the whole 
of its hydrogen is removed in the form of hydrochloric acid, and an equi- 
valent amount of chlorine is substituted for it, yielding the trichloride, 
formerly called sesquichloride of carton (C 2 C1 6 ) — 

C 2 H 4 C1 2 + Cl 8 = C 2 C1 6 + 4HC1. 

Trichloride of carbon is a white crystalline solid, with an aromatic 
odour rather like that of camphor. It fuses at 320° F., and boils at 360°, 



168 



BICHLORIDE OR TETRACHLORIDE OF CARBON. 



subliming unchanged. It is not dissolved by water, but is soluble in 
alcohol and ether. 

When the vapour of trichloride of carbon is passed through a tube 
containing fragments of glass heated to redness, it is decomposed into 
chlorine and a colourless liquid, which is the dichloride, formerly called 
protochloride of carbon (C 2 C1 4 ). It has an aromatic odour, and boils at 
248° F. ; is heavier than water (sp. gr. 1*5), which does not dissolve it, 
and is soluble in alcohol and ether. 

By passing the vapour of this dichloride of carbon through tubes heated 
to bright redness, it is decomposed into chlorine and monochloride, for- 
merly called subchloride of carbon (C 2 C1 2 ), which forms silky crystals 
almost free from odour, insoluble in water, but soluble in ether, and 
capable of being sublimed unchanged at a high temperature. It burns 
in air with a red smoky flame. 

Tetrachloride (bichloride) of carbon (CC1 4 ) has been mentioned (p. 150) 
as the final result of the action of chlorine upon marsh-gas (CH 4 ) and upon 
chloroform (CHC1 3 ). It is easily obtained in large quantity, by passing 
chlorine (dried by passing through a tube containing pumice wetted with 
strong sulphuric acid) (fig. 186) through a bottle containing bisulphide of 




Fig. 186. —Preparation of bichloride of carbon. 

carbon, and afterwards through a porcelain tube wrapped in sheet copper, 
and filled with fragments of broken porcelain, maintained at a red heat 
by a charcoal or gas furnace, and condensing the products in a bottle sur- 
rounded by ice. A mixture of tetrachloride of carbon and chloride of 
sulphur is thus obtained — 



CS 2 + Cl 6 - CC1 4 



+ S 2 C1 2 . 

Tetrachloride Chloride of 
of carbon. sulphur. 



Bisulphide of carbon. 

By shaking this mixture with solution of potash, the chloride of sulphur 
is decomposed and dissolved, whilst the tetrachloride of carbon separates 
and falls to the bottom. The upper layer having been poured off, the 
tetrachloride may be purified by distillation. 

Tetrachloride of carbon is a colourless liquid much heavier than water 
(sp. gr. 1*6), having a peculiar odour, and boiling at 172° F. It may be 
solidified at - 9° F. The tetrachloride is insoluble in water, but dissolves 
in alcohol and ether. 



OXYCHLOKIDE OF CAEBON. 



169 



By the action of chlorine on naphthaline (C 10 H 8 ) Laurent obtained, as 
the ultimate result, a crystalline chloride of carbon containing C 10 C1 8 , to 
which he gave the name ehlonaphthalise. 

It will be noticed that each of the compounds of chlorine with carbon, 
except the sesquichloride, has its parallel in the compounds of hydrogen 
with carbon;* thus — 

Acetylene C 2 H 2 corresponds to monochloride of carbon C 2 C1 2 
Olefiant gas CH, ,, dichloride „ CLCL 



Marsh-gas CH 4 



tetrachloride 



CC1 4 



The history of trichloride of carbon affords an instructive instance 
of the influence of the molecular weight of a compound upon its proper- 
ties. By passing the vapour of tetrachloride of carbon through a tube 
heated to dull redness, a liquid is obtained which is found by analysis to 
contain precisely the same proportions of carbon and chlorine as the solid 
trichloride above described, but the specific gravity of its vapour 
(H = l) is only 59*25, which is half that of the vapour of solid tri- 
chloride of carbon, showing that in the liquid compound the same propor- 
tions of carbon vapour and chlorine are condensed into a volume twice as 
large as in the solid trichloride, 2 vols, of the vapour of the liquid 
containing 1 vol. imaginary carbon vapour, and 3 vols, chlorine, and 
being represented by the formula CC1 3 . 

The following table exhibits the composition of the chlorides of 
carbon : — 

Chlorides of Carbon. 





Molecular 
Formulas. 


Molecular 
Volume. 


Molecular 
Weight. 


Monochloride, . 


c 2 ci 2 


2? 


95-0 


Dichloride, 


c 2 ci 4 


2 


166-0 


Trichloride (solid), 


c 2 ci 6 


2 


237-0 


(liquid), . 


CC1 3 


2 


118-5 


Tetrachloride, . 


CC1 4 


2 


154-0 



119. Oxy chloride of carbon, chlorocarbonic acid, or phosgene gas, is 
produced by the direct combination of equal volumes of carbonic oxide 
and chlorine gases under the influence of sunlight (whence its last name), 
when the mixture condenses to half its volume of a colourless gas, con- 
densable by cold, having a very peculiar pungent smell, and fuming 
strongly when exposed to moist air, decomposing the moisture and pro- 
ducing hydrochloric acid; C0.C1 2 + H 2 = C0 2 + 2HC1. It is not a true 
acid, for it is decomposed by bases, producing chlorides and carbonates. 
It is sometimes found useful in chemical research for removing hydrogen 
from organic compounds, and introducing carbonic oxide, or its elements, 
into its place. Its action on ammonia affords an example of this — 



4(NH 3 ) + CO.Cl 2 "= COH 4 lSr 2 + 



Urea. 



2(NH 8 .HC1) 

Hydrochlorate of 
ammonia. 



* When vapour of dichloride of carbon is mixed with hydrogen, and passed through 
a red-hot tube, olefiant gas and hydrochloric acid are produced. The tetrachloride, under 
similar circumstances, yields marsh-gas. 



170 CHLORIDE OF NITROGEN. 

in which two molecules of NH 3 have been decomposed, two atoms of the 
hydrogen having been removed in the form of hydrochloric acid, and 
replaced by a molecule of carbonic oxide. 

120. Chloride of silicon, unlike the chlorides of carbon, maybe formed 
by the direct union of silicon with chlorine at a high temperature; but it 
is best prepared by passing dry chlorine over a mixture of artificial silica 
and charcoal, heated to redness in a porcelain tube connected with a 
receiver kept cool by a freezing -mixture. Neither carbon nor chlorine 
separately will act upon the silica, but when they are employed together, 
the carbon removes the oxygen and the chlorine combines with the sili- 
con— Si0 2 + C 2 + CI, - SiCl 4 + 2CO. 

The chloride of silicon is a colourless heavy liquid (sp. gr. 1*52) which 
is volatile (boiling point, 138° F.), and fumes when exposed to air, the 
moisture of which decomposes it, yielding hydrochloric and silicic acids — 

SiCl 4 + 2H 2 = Si0 2 + 4HC1. 

Although it has received no practical application on a large scale, the 
chloride of silicon is valuable to the chemist as a convenient source of 
compounds of silicon, which could not easily be procured from the very 
unchangeable silicic acid. 

By passing hydrochloric acid over silicon heated to redness, a very remarkable 
liquid is obtained, which is much more volatile than the chloride of silicon (boiling 
point, 108° F.), and, unlike most chlorine compounds, is inflammable, burning with 
a greenish flame, and producing silica and hydrochloric acid. It fumes strongly in 
air, and is decomposed by water, yielding hydrochloric acid, and the substance termed 
leukone. The composition of this liquid appears to be Si 3 H 4 Cl 10 , and its production 
would be represented by the equation Si 3 + 10HCl=Si 3 H 4 Cl 10 + H 6 . Its decomposi- 
tion by water would be explained by the equation — 

Si 3 H 4 Cl 10 + 5H 2 = Si 3 H 4 5 + 10HC1. 

Leukone. 

The chloride of ooron (BC1 3 ) is similar in its general character to the 
chloride of silicon, and is prepared by a similar process, but it is a gas 
instead of a liquid at ordinary temperatures. 

121. Chloride of nitrogen is the name usually given to the very explo- 
sive compound before referred to as being produced by the action of 
chlorine on sal-ammoniac. • Its composition is somewhat uncertain ; its 
explosive character rendering its exact analysis very difficult. Some 
chemists regard it as NC1 3 , that is, ammonia in which all the hydrogen 
has been displaced by chlorine, whilst others believe it to contain hydrogen, 
regarding it as derived from two molecules of ammonia (NH 3 .NH 3 ), by the. 
substitution of five atoms of chlorine for five of hydrogen (isTCl 3 .NHCl 2 ). 

It is a yellow, heavy, oily liquid (sp. gr. 1'65), which volatilises easily, 
yielding a vapour of very characteristic odour, which affects the eyes. 
When heated to about 200° F. it explodes with great violence, emitting a 
loud report and a flash of light. Its instability is, of course, attributable 
to the feeble attraction which holds its elements together ; and the violence 
of the explosion, to the sudden expansion of a small volume of the liquid 
into a large volume of nitrogen, chlorine, and perhaps hydrochloric acid. 
As might be expected, its explosion is at once brought about by contact 
with substances which have an attraction for chlorine, such as phosphorus 
and arsenic ; the oils and fats cause its explosion, probably by virtue of 
their hydrogen ; oil of turpentine explodes it with greater certainty than 
the fixed oils. Alkalies also decompose it violently ; whilst acids, having 



PREPARATION OF CHLORIDE OF NITROGEN. 



171 




Fig. 187. 



no action upon the chlorine, are not so liable to explode it. At 160° F. 
this substance has actually been distilled without explosion. 
• Although practically unimportant, the violent explosive properties of 
this substance render it so interesting that it may be well to give some 
directions for its safe preparation. 

Preparation of chloride of nitrogen. — Dissolve 4 oz. of sal-ammoniac in 48 oz. 
(measured) of water, in a porcelain dish, at a gentle heat. Filter the solution, and 
pour it into a shallow leaden dish (A, fig. 187), previously cleaned from all grease by 
boiling a little solution of potash in it. Place in 
the solution a smaller leaden dish (B) (capacity, 
1^ oz.), cleaned in the same way, and furnished 
with a copper wire handle. 

Cut off the neck of a Florence flask (by scratch- 
ing with a file, and leading the crack round with 
a red-hot iron), clean it by boiling a little potash 
in it, rinse it in water, and attach it to a string, so 
that it may be suspended, in an inverted position, 
upon a stand. 

When the temperature of the solution of sal-ammoniac has fallen to nearly 90° F., 
fill the Florence flask with water in the pneumatic trough, and displace the water 
by chlorine, passed up from a gas bottle free from grease. Close the flask with a 
watch-glass placed under the orifice, and suspend it by the string from a stand (fig. 
188), so that its mouth may be about an inch below the surface of the solution of 
sal-ammoniac, and immediately over the 
centre of the small leaden dish. Remove 
the watch-glass, and let the whole arrange- 
ment be placed where the explosion can 
do no harm. The solution will soon begin 
to absorb the chlorine and to rise in the 
flask, whilst yellow oily globules form upon 
its surface, occasionally collecting into a 
larger one, which falls through the solution 
into the small leaden dish. When the 
flask is nearly filled with the solution which 
will require about twenty minutes, gently 
raise the flask, from a distance, by hooking 
the string with a wire at the end of a long 
stick, and allow the solution to flow gently out of it into the leaden dish. Place 
the flask at a safe distance, lest there should be any chloride of nitrogen still clinging 
to it. Examine the leaden dishes to see where the oily globules have fallen, lifting 
out the smaller dish by hooking its wire handle with a long stick. Explode the 
globules from a safe distance with a stick dipped in turpentine. A good explosion 
will throw the solution up several feet, and will raise a large leaden dish several 
inches into the air, indenting it deeply at the seat of the explosion. 

Another method of preparing the chloride, when it is not desired to examine it 
closely, but merely to witness the explosion, consists in acting upon sal-ammoniac 
with solution of hypochlorous acid ; but as this does not succeed in a leaden vessel, 
and must be performed in glass or porcelain, the action should be conducted at a 
distance from the operator, lest he be wounded by the fragments of the vessel. 

Fifty grains of red oxide of mercury are very finely powdered, and thrown into a 
pint bottle of chlorine together with 4 oz. (measured) of water. The stopper is 
3 eplaced, and the bottle well shaken, loosening the stopper occasionally, 
as long as the chlorine is absorbed. The solution of hypochlorous acid 
thus produced is filtered from the residual oxj^chloride of mercury, and 
poured into a clean thumb-glass (fig. 189). A lump of sal-ammoniac 
weighing 20 grains is then dropped into the solution, and the glass is 
placed in a safe situation where the explosion will do no harm. After 
the lapse of twenty minutes, the chloride of nitrogen may be exploded 
from a safe distance (9 feet) by touching it with a stick dipped in 
turpentine. The glass will be shattered into very small fragments, 
and the operator will be safer behind a screen, unless protected by 
and leather gloves. 

122. Aqua regia. — This name has been bestowed upon the mixture of 




Fig. 188. 




Fig. 189. 
fencing-mask 



172 EXTRACTION OF BROMINE. 

(1 measure of) nitric, and (3 measures of) hydrochloric acid (nitromuriatic 
acid) which is employed for dissolving gold, platinum, and other metals 
which are not soluble in the separate acids. If a little gold leaf be placed 
in hydrochloric and nitric acids contained in separate glasses, the metal 
will remain unaffected even on warming the acids, but if the contents of 
the glasses be mixed, the gold will be immediately dissolved by the 
chlorine which is liberated in the action of the acids upon each other — 

HN0 3 + 3HC1 = 2H 2 + NOCl 2 + CI. 

Chloronitric gas. 

The chloronitric gas which is formed does, not act upon the gold, but is 
evolved as a red gas, condensable in a freezing mixture to a dark red 
liquid. It has a very peculiar odour, and is decomposed by contact with 
water into hydrochloric acid and nitric peroxide — 

NOCl 2 + H 2 = 2HC1 + M) 2 . 

A similar, though somewhat less volatile substance, called chloronitrous gas 
and having the formula NOC1, is produced by mixing 2 volumes of nitric 
oxide with 1 volume of chlorine ; it condenses to a red liquid at 0° F. ; it 
is also produced in small quantity by the action of hydrochloric acid on 
nitric acid; HN0 3 + 3HC1 = 2H 2 + NOC1 + Cl 2 . 



BBOMHSTE. 

Br = 80 parts by weight. 

123. It generally happens that elements between which any strong 
family likeness exists are found associated in nature. This remark par- 
ticularly applies to the three elements — chlorine, bromine, and iodine, all 
of which are found in sea water, though- the first predominates to such 
an extent that the others for a long time escaped notice. Bromine was 
brought to light in the year 1826 by Balard in the examination of bittern, 
which is the liquid remaining after the chloride of sodium and some 
other salts have been made to crystallise by evaporating sea water, which 
contains only about one grain of bromine per gallon, in the forms of 
bromide of magnesium and 'bromide of sodium. It is also extracted from 
the waters of certain mineral springs, as those of Kreuznach and Kissin- 
gen, which contain much larger quantities of bromine, either as bromide 
of potassium or of sodium or magnesium. During the last few years, 
much bromine has been obtained from the mother-liquors of the salt- 
works at Stassfurth, and from saline springs in the United States. 

In extracting the bromine from these waters, advantage is taken of the 
circumstance that chlorine is capable of displacing bromine from its 
combinations with the metals. After most of the other salts, such as 
chloride of sodium, sulphate of soda, and sulphate of magnesia, which 
are less soluble than the bromides, have been separated from the water 
by evaporation and crystallisation, the remaining liquid is subjected to the 
action of chlorine gas, when it acquires an orange colour, due to the 
liberation of the bromine ; KBr + CI = KC1 + Br. The bromine thus 
set free exists now diffused through a large volume of water which can- 
not be separated from it in the usual way by evaporation, because bromine 
is itself very volatile. An ingenious expedient is therefore resorted to of 
shaking the orange liquid briskly with ether, which has a greater solvent 



EXTRACTION OF BROMINE. 173 

power for bromine than is possessed by water, and therefore abstracts it 
from the aqueous solution ; since ether does not mix to any great extent 
with water, it now rises to the surface of the liquid, forming a layer of a 
beautiful orange colour, due to the bromine which it holds in solution. 
This orange layer is carefully separated, and shaken with solution of 
potash, which immediately destroys the colour by removing the bromine, 
leaving the ether to rise to the surface in a pure state, and fit to be em- 
ployed for abstracting the bromine from a fresh portion of the water. 
The action of the bromine upon potash is precisely similar to that of 
chlorine — 

6KHO + Br 6 = 5KBr + KBr0 3 + 3H. 2 0. 

Bromide of Bromate of 
potassium. potash. 

After the solution of potash has been several times shaken with the 
ethereal solution of bromine, and has become "highly charged with this 
element, it is evaporated so as to expel the water, leaving a solid residue 
containing the bromide of potassium and bromate of potash. This saline 
mass is strongly heated to decompose the bromate of potash, and convert 
it into bromide of potassium — KBr0 3 = KBr + 3 . 

From this salt the bromine is extracted by distilling it with binoxide of 
manganese and sulphuric acid, when the potassium is oxidised at the 
expense of the binoxide of manganese, and the bromine is liberated and 
condensed in a receiver kept cool by iced water — 

2KBr + Mn0 2 + 2(H 2 O.S0 3 ) = K 2 O.S0 3 + MnO.S0 3 + 2H 2 + Br 2 . 

The aspect of the bromine so produced is totally different from that of 
any other element, for it distils over in the liquid condition, and pre- 
serves that form at ordinary temperatures, being the only liquid non- 
metallic element. Its dark red-brown colour, and the peculiar orange 
colour of the vapour which it exhales continually, are also characteristic ; 
but, above all, its extraordinary and disagreeable odour, from which it 
derives its name (/?pw/u,os, a stench), leaves no doubt of its identity. The 
odour has some slight resemblance to that of chlorine, but is far more 
intolerable, often giving rise to great pain, and sometimes even to bleed- 
ing at the nose. 

Liquid bromine is thrice as heavy as water (sp. gr. 2*96), and boils at 
145° F., yielding a vapour 5 J times as heavy as air (sp. gr. 5*54). It 
may be frozen at - 12° F. to a brown crystalline solid. It requires 33 
times its weight of cold water to dissolve it, and is capable of forming a 
crystalline hydrate (Br.5H 2 0) corresponding to hydrate of chlorine. 

In its bleaching power, its aptitude for direct combination, and its 
other chemical characters, it very closely resembles chlorine— so closely, 
indeed, that it is difficult to distinguish, in many cases, between the com- 
pounds of chlorine and bromine with other substances, unless the elements 
themselves be isolated. A necessary consequence of so great a similarity 
is, that very little use has been made of bromine, since the far more abun- 
dant chlorine fulfils nearly all the purposes to which bromine might 
otherwise be applied. In the daguerreotype and photographic arts, how- 
ever, some special applications of bromine have been discovered, and for 
some chemical operations, such as the determination of the illuminating 
hydrocarbons in coal-gas, bromine is sometimes preferred to chlorine. It 
has also been used in America as a disinfectant. The bromides of potas- 



174 



HYDROBROMIC ACID. 



sium and ammonium are frequently employed in medicine. In the com- 
position of their compounds, chlorine and bromine exhibit great analogy. 

Hypobromous acid has been obtained in solution by shaking oxide of 
mercury with water and bromine. The solution is very unstable, decom- 
posing, especially when heated, with liberation of bromine and formation 
of bromic acid. The action of bromine upon diluted solutions of the 
alkalies, and upon the alkaline earths, produces bleaching liquids similar 
to those formed by chlorine. 

Bromic acid (HBr0 3 ) can be prepared in a similar manner to chloric 
acid, to which it has a great general resemblance, the bromates being also 
similar to the chlorates. 

124. Hydrobromic acid (HBr = 81 parts by weight = 2 vols.). — The 
inferiority of bromine to chlorine in chemical energy is well exemplified 
in its relations to hydrogen, for the vapour of bromine mixed with hydro- 
gen will not explode under the action of flame or of the electric spark, 
like the mixture of chlorine and hydrogen. Direct combination may, 
however, be slowly induced by contact with heated platinum. 

When it is attempted to prepare this acid by distilling bromide of 
sodium or potassium with sulphuric acid (as in the preparation of hydro- 
chloric acid, the inferior stability of hydrobromic acid is shown by the 
decomposition of a part of it, the hydrogen being oxidised by the sulphuric 



acid, and the bromine set free ; 2HBr + H 2 O.S0 3 



2H 2 



SO. + Br n 



If a strong solution of phosphoric acid be employed instead of the 
sulphuric, pure hydrobromic acid may be obtained. 

But the most instructive method of obtaining hydrobromic acid consists 
in attacking water with bromine and phosphorus simultaneously, when 
the phosphorus takes the oxygen of the water, forming iDhosphorous acid, 
and the bromine combines with the hydrogen to form hydrobromic acid — 

6H 2 + Br 6 + P 2 = 3H 2 O.P 2 3 + 6HBr. 

Hydrated 
phosphorous acid. 

Probably bromide of phosphorus (PBr 3 ) is formed as an intermediate 

stage. 

The experiment may be made in a W-formed tube (fig. 190), one bend of which 
contains 40 grains of phospho'rus in fragments intermingled with glass moistened 
with water, whilst the other bend contains 240 grains 
of bromine (about one drachm). This limb of the tube 
is corked, and the other furnished with a delivery 
tube, so that the gas may be collected either by down- 
ward displacement or over mercury. The bromine is- 
slightly heated, when it distils over to the moist phos- 
phorus, and hydrobromic acid is evolved. A moderate 
heat should afterwards be applied to the moist glass, 
to expel part of the hydrobromic acid from the water. 

Hydrobromic acid is very similar to hydro- 
chloric acid ; it liquefies at - 92° P., and has 
been solidified by a still . lower temperature, 
which is not the case with hydrochloric acid. 
Like that gas it is very soluble in water, and 
the solution acts upon metals and their oxides in the same manner as 
hydrochloric acid. Chlorine removes the hydrogen from hydrobromic 
acid, liberating bromine, which it converts into chloride of bromine if 
employed in excess. 

Bromide of nitrogen has been obtained by the action of bromide of 




Fig. 190. — Preparation of 
hydrobromic acid. 



DISCOVERY OF IODESTE. 175 

potassium upon chloride of nitrogen, which it resembles in general 
character and explosive properties. 

Chloride of bromine is a very volatile yellow liquid of pungent odour. 
Its composition is not certainly known. That chlorine should unite 
directly with bromine, which it so much resembles in chemical character, 
illustrates its great tendency to direct chemical combination. 



IODINE. 

1 = 127 parts by weight. 

125. Iodine is contained in sea water in even smaller quantity than 
bromine, but the iodide of sodium appears to constitute a portion of the 
necessary food of certain varieties of sea-weed, which extract it from the 
sea-water, and concentrate it in their tissues. . The ash remaining after 
sea-weed has been burnt was long used, under the name of kelp, in soap- 
making, because it contains a considerable quantity of carbonate of soda ; 
and in the year 1811, Courtois, a soap-boiler of Paris, being engaged in 
the manufacture of soda from kelp, obtained from the waste liquors a 
substance which possessed properties different from those of any form of 
matter with which he was acquainted. He transferred it to a French 
chemist, Clement, who satisfied himself that it was really a new substance, 
and Gay-Lussac and Davy having examined it still more closely, it took 
its rank among the non-metallic elementary substances, under the name 
of iodiue (iwcfys, violet-coloured), conferred upon it in allusion to the 
magnificent violet colour of its vapour. 

This history of the discovery of iodine affords a very instructive example 
of the advantage of training persons engaged in manufactures to habits of 
accurate observation, and, if possible, of accurate chemical observation ; 
for had Courtois passed o^ver this new substance as accidental, or of no 
consequence, the community would have lost, at least for some time, the 
benefits derived from the discovery of iodine. 

For some years the new element was only known as a chemical 
curiosity, but an unexpected demand for it at length arose on the part of 
the physician, for it had been found that the efficacy of the ashes of 
sponge, which had long been used in some particular maladies, was due 
to the small quantity of iodine which they contained, and it was, of course, 
thought desirable to place this remedy in the hands of the medical pro- 
fession in a purer form than the ash of sponge, where it is associated with 
very large quantities of various saline substances. Much more recently 
the demand for this element has greatly increased, on account of its employ- 
ment in photography, and large quantities of it are annually produced 
from kelp, the collection and burning of which affords occupation to the 
very poor inhabitants of some parts of the coasts of Ireland and Scotland, 
who would otherwise have been thrown out of work when soda began to 
be manufactured from common salt, and the demand for kelp as the source 
of that alkali had ceased. The sea-weed is spread out to dry, and burnt 
in shallow pits at as low a temperature as possible, for the iodide of sodium 
is converted into vapour and lost if the temperature be very high.* The 
ash, which is left in a half-fused state, is broken into fragments and 
treated with hot water, which dissolves about half of it, leaving a residue, 
consisting of carbonate and sulphate of lime, sand, &c. The whole of the 

* The sea-weed is often only charred and not incinerated, so as to avoid loss of iodine, 



176 



PROPERTIES OF IODINE. 




191. — Extraction of iodine. 



iodide of sodium is contained in the portion dissolved by the water, "but is 
mixed with much larger quantities of sulphate of soda, carbonate of soda, 
chloride of potassium, hyposulphite of soda, and sulphide of sodium. A 
portion of the water is expelled by evaporation, when the sulphate of 

soda, carbonate of soda, and 
chloride of potassium, being 
far less soluble than the 
iodide of sodium, crystal- 
lise out. In order to de- 
compose the hyposulphite 
of soda and the sulphide of 
sodium, the liquid is mixed 
with an eighth of its bulk 
of oil of vitriol, which de- 
composes these salts, evolv- 
ing sulphurous and hydro- 
sulphuric acid, with de- 
position of sulphur, and 
forming sulphate of soda, 
which is deposited in crys- 
tals. The liquor thus pre- 
pared is next mixed with 
binoxide of manganese, and heated in a leaden retort (fig. 191), placed in 
a sand-bath, when the iodine is evolved as a magnificent purple vapour, 
which condenses in the globular glass receivers in the form of dark grey 
scales with metallic lustre, and having considerable resemblance to black 
lead. The liberation of the iodine is explained by the following equa- 
tion — 

2NaI + Mn0 2 + 2(H,O.S0 3 ) = Na 2 O.S0 3 + MnO.S0 3 + 2R 2 + 1, . 

The distillation is conducted at a temperature below 212°, to avoid the 
liberation of chlorine from the chloride of sodium, and the consequent 
formation of chloride of iodine. 

Several processes have been devised to render the extraction of the iodine from the 
concentrated solution of kelp easier and more economical. The most promising is 
very similar to that employed for separating bromine (p. 172). The iodine is 
liberated by chlorine, and extracted from the liquid by shaking it with benzole ; by 
treating the benzole with solution of potash, the iodine is converted into a mixture 
of iodide of potassium and iodate of potash, from which the iodine may be precipi- 
tated by acidifying with hydrochloric acid. 

6KHO + I 6 = 5KI -»■ KI0 3 + 3H 2 
5KI + KI0 3 + 6HC1 = 6KC1 + 3H 2 + I 6 . 

The features of this element are extremely well marked ; its metallic 
lustre and peculiar odour sufficiently distinguish it from all others, and 
the effect of heat upon it is very striking, in first easily fusing it (at 225° 
F.), and afterwards converting it (boiling point, 347° F.) into the most 
exquisitely purple vapour, which is nearly nine times as heavy as air (sp. 
gr. 8-72), and condenses upon a cool surface in shining scales. It stains 
the skin intensely brown if handled. The specific gravity of solid iodine 
is 4-95. 

When iodine is shaken with cold water a very small quantity is dis- 
solved, forming a light brown solution, which decomposes slowly at the 
ordinary temperature, the iodine combining with the hydrogen of the 



PROPERTIES OF IODINE. 177 

water. Hot water dissolves a larger quantity, but alcohol is one of the 
best solvents for iodine, producing a dark red-brown solution (tincture of 
iodine) from which part of the iodine may be precipitated by adding 
water. A solution of iodide of potassium also dissolves iodine freely. 
Benzole and bisulphide of carbon dissolve it abundantly, producing fine 
violet-red solutions, which deposit the iodine, if allowed to evaporate 
spontaneously, in minute rhombic octahedral crystals aggregated into very 
beautiful fern-like forms. If an extremely weak aqueous solution ot 
iodine be shaken with a little bisulphide of carbon, the latter will remove 
the iodine from the solution, and on standing, will fall to the bottom of 
the liquid, having a beautiful violet colour. By dissolving a large quan- 
tity of iodine in bisulphide of carbon, a solution is obtained which is 
perfectly opaque to rays of light, though it allows heat-rays to pass freely, 
and is, therefore, of great value in physical experiments. A solution of 
iodine in bichloride of carbon is also used for the same purpose. 

Existing, as iodine does, in very minute quantity in the water from 
various natural sources, it would often be overlooked if the chemical 
analyst did not happen to possess a test of the most delicate description 
for it. 

Iodine, in the uncombined state, dyes starch of a beautiful blue colour, 
as may be proved by heating a grain or two of the element with water, 
and adding to the solution a little thin starch (seep. 53), or by placing a 
minute fragment of iodine in a stoppered bottle, and suspending in it a 
piece of paper dipped in thin starch. This test, however, though sensi- 
tive to the smallest quantity of free iodine, gives no indication whatever 
with iodine in combination, as it always exists in nature ; in order, there- 
fore, to test for iodine, a little starch-paste is added to the suspected 
liquid, and then a drop of a weak solution of chlorine, which will set free 
the iodine, and cause the production of the blue colour. Characters 
written on paper with a brash dipped in a mixture of iodide of potassium 
and starch, are brought out in blue by pouring a little chlorine-gas upon 
them. It is necessary, however, carefully to avoid adding too much chlo- 
rine, since it would immediately destroy the colour of the iodised starch. 
Alkalies also bleach it, and the colour of a mixture of the iodised starch 
with water is removed by heating, but returns in great measure when the 
solution cools. 

Though very closely connected with chlorine and bromine in its gene- 
ral chemical relations, there are several points in the history of iodine which 
cause it to stand out in marked contrast by the side of these elements. The 
attraction which binds it to hydrogen and the metals is certainly weaker 
than that exerted by chlorine and bromine, so that either of these is cap- 
able of displacing it from its compounds, and its bleaching properties are 
^ery feeble. On the other hand, it exhibits a more powerful tendency to 
unite with oxygen, for boiling nitric acid converts it into iodic acid (I 2 5 ), 
though this oxidising agent would not affect chlorine or bromine. 

Some of the compounds of iodine with the metals are remarkable for their beautiful 
colours. The iodide of mercury, produced by mixing solutions of iodide of potassium 
and chloride of mercury, forms a fine scarlet precipitate, which dissolves in an excess 
of iodide of potassium to a colourless solution. 

If this iodide of mercury be collected on a filter, washed and dried, it will be 
found, on heating a portion of it in a test-tube, that it acquires a fine yellow colour 
•and sublimes in golden yellow crystals, which resume the original red colour when 
rubbed with a glass rod. If it be spread upon paper and gently heated, the scarlet 
iodide becomes yellow, but the red colour returns on rubbing it with the thumb - 

M 



178 PERIODIC ACID. 

nail. These changes of colour are attended by an alteration in crystalline form, but 
not in the chemical composition of the iodide of mercury. This iodide is used in 
painting under the name of pure scarlet or iodine scarlet, but the colour is not 
durable. 

Iodide of lead has a bright yellow colour, as may be seen by precipitating iodide 
of potassium with a solution of acetate of lead. The precipitate is dissolved by 
boiling with water (especially on adding a little hydrochloric acid), forming a colour- 
less solution, from which the iodide of lead crystallises in very brilliant golden scales 
on cooling. Iodide of silver is produced as a yellow precipitate when nitrate of silver 
is added to iodide of potassium. The bromide and chloride of silver would form 
white precipitates. 

126. Oxides of iodine. — Although the compound I 2 0, corresponding to 
hypochlorous acid, is believed to exist, it has never yet been obtained in 
a separate state, the only known oxides of iodine being iodic acid (I 2 5 ) 
and periodic acid (I. 2 7 1) which has only been obtained in the hydrated 
state. 

Iodic acid. — It is most easily prepared by boiling iodine with the 
strongest nitric acid in a long-necked flask, when it is dissolved in the 
form of iodic acid which is left on evaporating the nitric acid, as a white 
mass. This may be purified by dissolving in water and crystallising, 
when the iodic acid forms white hexagonal tables, which have the com- 
position H3O.I3Og.2Aq. Heated to 266° F., they become H 2 O.I 2 5 , and 
at 360° F. the whole of the water is expelled, leaving anhydrous iodic acid, 
which is decomposed at about 700° F. into iodine and oxygen. The 
anhydrous iodic acid oxidises combustible bodies, but not with any 
great violence. The hydrate is far more stable than the hydrated 
chloric and bromic acids. Its solution first reddens litmus paper, and 
afterwards bleaches it by oxidation. Its salts, the iodates, are less 
easily soluble in water than the chlorates and bromates. which they 
resemble in their oxidising action upon combustible bodies. They are 
all decomposed by heat, evolving oxygen, and sometimes even iodine, 
showing how much inferior this element is to chlorine and bromine in its 
attraction for metals. 

It is a remarkable feature of the iodates, that some of them contain two 
or even three molecules of iodic acid to one of base. Thus there are 
three iodates of potash, K 2 O.I 2 5 (or KI0 3 ) K 2 0.2I 2 5 , and K 2 0.3I 2 5 , 
No such compounds are known in the cases of chloric and bromic acids. 

Periodic acid is obtained from the basic periodate of soda formed by passing 
chlorine through a mixture of iodate of soda and free soda, when the latter is decom- 
posed, its sodium being abstracted by the chlorine, whilst its oxygen converts the 
iodic acid into periodic acid — 

Na 2 O.J 2 5 + 3Na a O + Cl 4 = 2Na 2 O.T 2 7 + 4NaCl . 

Basic periodate of 
soda. 

This periodate of soda is deposited, being sparingly soluble in water, a most 
unusual circumstance with salts of soda. By dissolving it in nitric acid, and adding 
nitrate of silver, a basic periodate of silver is obtained, which is yellow when precipi- 
tated from cold, and red from hot solutions — 

2Na 2 O.I 2 7 + 4(AgN0 3 ) = 2Ag 2 O.I 2 7 + 4(JsTaN0 8 ). 

Basic periodate of v .,„ . „,' ,„ 
s "Q Ver IS urate of soda. 

When the silver salt is dissolved in nitric acid, it is decomposed into nitrate of 
silver, which remains in solution, and neutral periodate of silver, which is deposited 
in crystals — 

2Ag 2 0.I 2 O 7 + H 2 O.KA = Ag 2 O.I 2 7 + Ag 2 O.N 2 5 + H 2 . 



HYDRIODIC ACID. 



179 



When neutral periodate of silver is boiled with water, it again yields the insoluble 
basic periodate of silver, and hydrated periodic acid is found in the solution — 

2(Ag 2 O.I 2 7 ) + E 2 = 2Ag 2 O.I0 7 + H 2 O.I 2 7 . 

On evaporating the solution, the hydrated periodic acid is deposited in prismatic 
crystals having the composition H 2 O.I 2 7 .4Aq,which lose their water at about 320° 
F., and are decomposed into iodic acid and oxygen at 400° F. The solution of 
periodic acid, of course, exhibits oxidising properties. 

The periodates are remarkable for their sparing solubility in water ; they are easily 
decomposed by heat, like the iodates. It will have been remarked, in the above 
account of the preparation of periodic acid, that this acid exhibits a great tendency 
to the formation of basic salts, whilst iodic acid is remarkable for its acid salts. 

127. Hydriodic acid (HI = 128 "parts by weight = 2 vols.). — Iodine 
vapour combines with hydrogen, under the influence of heated platinum, 
to form hydriodic acid gas. The gas is best prepared by decomposing 
water with iodine in the presence of phosphorus, so as to produce hydri- 
odic acid and rmosphoric acid, which is allowed to act upon iodide of 
potassium in order to produce more hydriodic acid — 



8H s O + I 10 + P 2 = 


10HI + 3H 2 O.P 2 5 and 


4KI + 3H 2 O.P 2 5 


= 4HI + 2K 2 O.H 2 O.P 2 5 

Phosphate of potash. 



100 grains of iodide of potassium are dissolved in 50 grains of water in a retort 
(fig. 192), and 200 grains of iodine are added ; when this has dissolved, 10 grains 
of phosphorus are introduced, and the mixture 
heated very gradually, the gas being collected 
by downward displacement in stoppered bottles, 
which must be placed in readiness, as the gas 
comes otf very rapidly. These cpuantities will 
fill four pint bottles with the gas. 







Pie. 192. 



Preparation of hydriodic 
acid. 



Hydriodic acid gas is very similar in 
its properties to hydrochloric and hydro- 
bromic acids, fuming strongly in moist 
air, very readily absorbed by water, lique- 
fied only under strong pressure, and soli- 
dified by extreme cold. It is much 
heavier, its specific gravity being 4*44. 

If a bottle of hydriodic acid gas be placed in contact with a bottle 
containing chlorine or bromine vapour diluted with air (fig. 149), 
it will be instantly decomposed, with separation of the beautiful violet 
vapour of iodine. 

The aqueous solution of hydriodic acid is most conveniently prepared 
by passing hydrosulphuric acid gas through water in which iodine is sus- 
pended, H 2 S + I 2 = 2HI + S, the separated sulphur being filtered off, 
and the solution boiled to expel the excess of hydrosulphuric acid. 
Solution of hydriodic acid differs greatly from hydrochloric and hydro- 
bromic acids, in being decomposed by exposure to air, its hydrogen being 
oxidised and iodine separated, which dissolves in the liquid and renders 
it brown. 

This tendency of the hydrogen of hydriodic acid to combine with 
oxygen renders that acid a powerful reducing agent. It is even capable 
of converting hydrated sulphuric acid into hydrosulphuric acid — 



H 2 O.S0 3 



SHI 



H S + 4H 2 



so that when iodide of potassium is heated with concentrated sulphuric 
acid, hydrosulphuric acid is evolved in considerable quantity. 



180 IODIDE OF POTASSIUM. 

The action of hydriodic acid upon the metals and their oxides is gene- 
rally similar to that of the other hydrogen acids. 

When potassium is heated in a measured volume of hydriodic acid, the 
iodine is removed, and the hydrogen occupies half the original volume. 
Hence 1 volume of hydrogen is combined with 1 volume of iodine vapour 
in 2 volumes of hydriodic acid. 

Like chlorine and bromine, iodine is capable of displacing hydrogen 
from many organic compounds, and of taking its place, but its action in 
this respect is much feebler. The circumstance that the organic com- 
pounds containing iodine are generally much less volatile, and therefore 
more manageable than those of chlorine and bromine, leads to the exten- 
sive employment of this element in researches upon organic substances. 

With olefiant gas, iodine forms a crystalline solid compound (C 2 H 4 I 2 ) 
corresponding to Dutch liquid (p. 92), and from this compound a yellow 
unstable aromatic liquid has been obtained, which is believed to be an 
iodide of carbon. 

128. Iodide of nitrogen. — The action of chlorine, bromine, and iodine 
upon ammonia, exemplifies the difference in their attraction for hydrogen ; 
for whilst chlorine and bromine, acting upon ammonia, cause the libera- 
tion of a certain amount of nitrogen, iodine simply removes two-thirds of 
the hydrogen, and itself fills up the vacancies thus occasioned, no nitrogen 
being liberated, NH 3 + I 4 = NHI 2 + 2HIj the hydriodic acid thus formed 
combining with more ammonia to form hydriodate of ammonia. 

To prepare the iodide of nitrogen, 20 grains of iodine are rubbed to powder in a 
mortar and mixed with half an ounce (measured) of strong ammonia ; the mortar 
is covered with a glass plate, and after about half an hour the iodide of nitrogen is 
collected in separate portions upon four filters, which are allowed to drain and 
spread out to dry. The brown solution contains iodine dissolved in hydriodate of 
ammonia. 

The iodide is a black powder, which explodes with a loud report even 
when touched with a feather, emitting fumes of hydriodic acid and purple 
vapour of iodine ; its explosion is probably represented by the equation — 

NHI 2 = -K + HI " + I, 
its violence being accounted for by the sudden evolution of a large volume 
of gas and vapour from a small volume of solid. Even when allowed to 
fall from the height of a few feet upon the surface of water, it explodes if 
perfectly dry. In the moist state it slowly undergoes decomposition. 

129. Iodine forms two compounds with chlorine, the protochloride of 
iodine (IC1) and the ter chloride (IC1 3 ). The former is a brown volatile 
liquid of irritating odour, obtained by distilling 1 part of iodine with 4 
parts of chlorate of potash. 

The terchloride forms fine red needle-like crystals, and is produced when 
iodine is acted upon with an excess of chlorine. Bromides of iodine have 
also been obtained, but their composition is not well known. 

130. Iodide of potassium (KI = 166 parts by weight). This salt is 
the most useful compound of iodine, being largely employed in medicine 
and in photography. It is generally prepared by decomposing iodide of 
iron with carbonate of potash. 

The iodide of iron (also a useful medicine) is made by placing two 
parts of iodine in contact with one part of iron filings and ten parts of 
water. The iodine combines with part of the iron, evolving considerable 
heat, and producing the iodide of iron (Fel 2 ). 



FLUORINE — HYDROFLUORIC ACID. 181 

The liquid is decanted from the excess of iron, and one-third of the 
weight of iodine previously employed is dissolved in it. In this way, two- 
thirds of the iodide of iron are converted into per-iodide (Fe 2 I 6 ), so that 
the solution contains a mixture of one molecule of the iodide (Fel 2 ) and 
one of the per-iodide (Fe 2 I 6 ). It is now boiled, and carbonate of potash 
is gradually added as long as it causes a dark green precipitate of magnetic 
oxide of iron — 

Fel 2 + Fe 2 I 6 + 4(K 2 O.C0 2 ) = 8X1 + FeO.Fe 2 3 + 4CO, 

the carbonic acid is evolved with effervescence, and if the solution be 
filtered and evaporated, it deposits beautiful cubical (or sometimes octa- 
hedral) crystals, which are generally milk-white and opaque, but occa- 
sionally quite transparent. Pure iodide of potassium remains dry in 
ordinary air, but if an excess of carbonate of potash is employed in its 
preparation, the crystals retain some of that salt and become damp when 
exposed to air. The iodide of potassium dissolves easily in water and 
alcohol. If the solution be pure, it does not become coloured when mixed 
with pure hydrochloric acid ; but if any iodate of potash be present in 
it, a brownish colour will be produced, due to iodine liberated in the 
action of the iodic acid upon the hydriodic acid; I 2 5 + 10HI = I 12 + 5H 2 0. 
The iodate of potash is liable to be present in those specimens which are 
prepared by dissolving iodine in potash, to obtain a mixture of iodide of 
potassium and iodate of potash (see p. 176), the latter salt being after- 
wards decomposed by heat. 



FLUOKIKE. • 

F = 19 parts by weight. 

131. The most ornamental mineral substance occurring in any abun- 
dance in this country is known as fluor spar or Derbyshire spar (fluoride 
of calcium), and is found with several beautiful shades of colour — blue, 
purple, violet, or green, and sometimes perfectly colourless, either in large 
masses, or in crystals, which have the form of a cube or of some solid 
derived from it. The use of this mineral as a flux in smelting ores dates 
from a very remote period, and from this use the name fluor appears to 
have been originally derived, but we have no record of its chemical ex- 
amination till about a century since, when Margraf found his glass retort 
powerfully corroded in distilling this mineral with sulphuric acid, and 
Scheele soon after announced that it contained lime and fluoric acid ; but 
though this chemist had fallen into the 
error to which analysts are continually 
liable, of mistaking products for educts, 
his experiments, as they were afterwards 
perfected by Gay-Lussac and Thenard, 
deserve particular consideration. 



132. Hydrofluoric acid—(E¥ = 20 
parts by weight). — If powdered fluor spar 
be mixed with twice its weight of oil of 
vitriol, and heated in a leaden retort 
(fig. 193), the neck of which fits tightly 
into a leaden condensing-tube, cooled in a mixture of ice and salt, a 




182 HYDROFLUORIC ACID. 

colourless liquid distils over, and the residue in the retort is found to 
consist of sulphate of lime — * 

CaF 2 + H. 2 O.S0 3 = CaO.SO, + 2HF. 

Flu ? dde of Sulphate of lime. Hydrofluoric 

calcium. l acid. 

The colourless liquid (hydrofluoric acid) possesses most remarkable pro- 
perties ; it is powerfully acid, fumes strongly in the air, and has a most 
pungent irritating odour. If the air is at all warm the liquid begins to 
boil when taken out of the freezing mixture, and is soon entirely dissi- 
pated in vapour (boiling point, 60° F.) Should the operator have the mis- 
fortune to allow a drop to fall upon his hand, it will produce a very pain- 
ful sore, even its vapour producing pain under the finger nails. Its 
attraction for water is so great, that the acid hisses like red-hot iron when 
brought in contact with it. But its most surprising property is that of 
rapidly corroding glass, which has already been alluded to as -noticed by 
Margraf. Experiment soon proved that great analogy existed between 
the properties of this new acid and those of hydrochloric acid ; and 
Ampere was led to institute a comparison between them, which caused 
him to adopt the opinion that the acid was a hydrogen acid, containing a 
new salt radical which he named fluorine ; the name of the acid was then 
changed from fluoric to hydrofluoric acid. 

This liquid has since been proved to be a solution of hydrofluoric acid 
in water, for if it be distilled with anhydrous phosphoric acid, which 
retains the water, it evolves hydrofluoric acid gas, which resembles hydro- 
chloric acid gas in fuming strongly on contact with moist air, and being 
eagerly absorbed by water, but has a far more pungent odour. The per- 
fectly dry gas has very little action upon glass. 

Pure hydrofluoric acid is prepared by heating dry hydrofluate of potas- 
sium (KF.HF) to redness in a platinum apparatus. It is then obtained 
as a colourless liquid which boils at 67° F. and has the specific gravity 
0*988 at 55° F. The pure acid scarcely affects metals, excepting potas- 
sium and sodium. It corrodes glass, however, rapidly, though its vapour 
has little action on glass unless moisture is present. It combines eagerly 
with anhydrous sulphuric and phosphoric acids, with great evolution of 
heat, a circumstance in which it resembles water, and differs altogether 
from its more obvious analogue, hydrochloric acid. It is also found that 
it combines energetically with the fluorides of potassium and sodium, 
precisely as water combines with the oxides of those metals, whilst nothing 
of the kind is noticed in the case of hydrochloric acid. 

It is remarkable that the solution of hydrofluoric acid, in its concen- 
trated form, is not so heavy as a somewhat weaker acid. Thus, the acid 
of sp. gr. 1*06 acquires the sp. gr. 1*15 on addition of a little water, but 
on adding more water its sp. gr. is again reduced. It would hence appear 
that the acid of 1*15 is a definite hydrate of hydrofluoric acid ; its com- 
position corresponds to HF.2H 2 0. It distils unchanged at 248° F. 
The solution is generally kept in bottles made of gutta-percha. 

The action of hydrofluoric acid upon metals and their oxides resembles 
that of hydrochloric acid. It dissolves all ordinary metals except gold, 
platinum, silver, mercury, and lead. Strange to say, it has but little 
action on magnesium. 

* The mineral kryolite (fluoride of aluminum and sodium) maybe advantageously substi- 
tuted for fluor spar, being more easily obtained in a pure state. For preparing the acid on 
a large scale, iron retorts are employed. 



FLUORIDES. 183 

The property which renders this acid so useful to the chemist is its 
power of dissolving silica even in its most refractory form. When sand 
or flint reduced to powder is digested in a leaden or platinum vessel with 
hydrofluoric acid, it is gradually dissolved, and if the solution be evapo- 
rated, the whole of the silica will be found to have disappeared in the 
form of gaseous fluoride of silicon; Si0 2 "+ 4HF = SiF 4 + 2H 2 0. If 
the silicic acid be combined with a base, the metal will be left as a fluo- 
ride, decomposable by sulphuric or hydrochloric acid. This renders 
hydrofluoric acid a most valuable agent in the analysis of the numerous 
mineral silicates which resist the action of other acids. 

The corrosion of glass by hydrofluoric acid is now easily explained. 
Ordinary glass consists of silicate of soda or potash combined with silicate 
of lime or oxide of lead. The hydrofluoric acid attacks and removes the 
silica, and thus eats its way into the glass. 

In order to demonstrate the action of this acid upon glass, a glass plate is warmed 
sufficiently to melt wax, a piece of which is then rubbed over it, until the glass is 
covered with a thin and pretty uniform coating. Upon this a word or drawing may 
be engraved with a sharp point so that the lines shall expose the glass. A mixture 
of powdered fluor spar with concentrated sulphuric acid is then poured over it, and 
allowed to remain for a quarter of an hour ; the acid mixture is washed off, and the 
plate gently warmed to melt the wax, which may be wiped off with a little tow, 
when it will be found that the hydrofluoric acid evolved from the mixture has cor- 
roded those portions of the glass from which the graver had removed the wax. It 
has been attempted to apply this process to the production of engravings, but the 
brittleness of the plate has formed a very serious obstacle. 

If a leaden or platinum dish be at hand, it is better to place the glass to be etched 
over the dish containing the mixture of fluor spar and sulphuric acid exposed to a 
very gentle heat. 

The solution of hydrofluoric acid etches glass without deadening the 
surface as is the case with the vapour, but a solution of fluoride of potas- 
sium or ammonium mixed with sulphuric acid does produce a dead sur- 
face and is much used for engraving on glass. 

Many ingenious experiments have been made in order to obtain fluorine 
in the separate state, but it was found that it invariably combined with 
some portion of the material of the vessel in which the operation was 
conducted. The most successful of the early attempts to isolate fluorine 
appears to have been made, at the suggestion of Davy, in a vessel of 
fluor spar itself, which could not, of course, be supposed to be in any way 
affected by it. A greenish gas was obtained, possessing chemical proper- 
ties similar to those of chlorine, but of much higher intensity. The diffi- 
culty, however, of obtaining vessels of fluor spar adapted to these 
experiments appears to have prevented any complete investigation of this 
most interesting element. 

The most recent experiments, in which fluoride of silver was decom- 
posed by iodine, furnished a fluoride of iodine (IF 5 ) and iodide of 
silver. 

Solutions of the fluorides of potassium and the other alkali metals cor- 
rode glass slowly like hydrofluoric acid. These fluorides are capable of 
combining with the acid; thus fluoride .of potassium forms KF.HF, which, 
when dry, is a convenient source of hydrofluoric acid gas when moder- 
ately heated. The only fluoride possessed of much practical interest beside 
the fluoride of calcium is the mineral Jcryolite (Kpvos, frost), which is a 
double fluoride of aluminum and sodium (3NaF.ALF 3 ) found abundantly 
in Greenland, and valuable as a source of aluminum and soda. The topaz 



184 FLUORIDE OF SILICON. 

contains fluorine, but in what form of combination is not well known ; its 
other constituents are alumina and silica. 

Fluorides are also found, though in very small quantity, in sea water, 
and they have been discovered in plants and animals. Human bone con- 
tains about 2 per cent, of fluoride of calcium. 

It will be remembered that fluorine is the only element which is not 
known to form any compound with oxygen. 

133. Fluoride of silicon (SiF 4 = 104 parts by weight = 2 vols.).— If a 
mixture of powdered fluor spar and glass be heated, in a test-tube or 
small flask, with concentrated sulphuric acid, a gas is evolved which has 
a very pungent odour, and produces thick white fumes in contact with 
the air ; it might at first be mistaken for hydrofluoric acid, but if a glass 
rod or tube be moistened with water and exposed to the gas, the wet sur- 
face becomes coated with a white film, which proves, on examination, to 
be silicic acid. This result originated the belief that the gas consisted of 
fluoric (now hydrofluoric) acid and silica, but Davy corrected this view 
by showing that it really contained no oxygen, and consisted solely of 
silicon and fluorine. The gas is now called the fluoride of silicon, and 
represents silicic acid in which the oxygen has been displaced by the 
fluorine ; the change of places between these two elements in the above 
experiment is represented by the subjoined equation — 

2CaF 2 + Si0 2 + 2(H 2 O.S0 3 ) = 2(CaO.S0 3 ) + SiF 4 + 2H 2 . 

roar* Silica - Sulphuric acid. Sulphate of lime. F1 Ji[con ° f 

The formation of the crust of silica upon the wetted surface of the glass 
is due to a decomposition which takes place between the fluoride of silicon 
and the water, in which the oxygen and fluorine again change places — 

SiF 4 + 2H 2 = Si0 2 + 4HF. 

Since this latter equation shows that hydrofluoric acid is again formed, 
it would be expected that the glass beneath the deposit of silica would be 
found corroded by the acid ; this, however, is not the case, and when the 
experiment is repeated upon a somewhat larger scale, so that the water 
which has acted upon the gas may be examined, it will be found to hold 
in solution, not hydrofluoric acid, but an acid which does not act upon 
glass, and is composed of hydrofluoric acid and fluoride of silicon, so that 
the hydrofluoric acid produced when water acts upon the fluoride, com- 
bines with a portion of the latter to produce the new acid 2HF.SiF 4 , 
liydrofluo-silicie acid. 

For the preparation of fluoride of silicon, 1 oz. of fluor spar and 1 oz. of powdered 
glass are mixed together, and heated, in a Florence flask, with 7 oz. (measured) of 
oil of vitriol, the gas being collected in dry bottles by downward displacement (see 
fig. 177, p. 153. If a little of the gas be poured from one of the bottles into a flask 
rilled up to the neck with water, the surface of the latter will become covered with 
a layer of silica, so that if the flask be quickly inverted, the water will not pour from 
it, and will seem to have been frozen. In a similar manner, a small tube filled 
with water and lowered into a bottle of the gas, will appear to have been frozen 
when withdrawn. A stalactite of silica some inches in length may be obtained by 
allowing water to drip gently from a pointed tube into a bottle of the gas. Characters 
written on glass with a wet brush are rendered opaque by pouring some fluoride 
of silicon upon them. 

Fluoride of silicon is a substance of some importance in mineralogical chemistry, 
since, by its aid, certain crystallised minerals may be artificially obtained under con- 
ditions which are not unlikely to have attended the production of the natural crystals. 
Thus, the mineral staurotide or staurolite (a-TKupo;, a cross), or granatite or cross-stone, 



HYDROFLUO-SILICIC ACID. 



185 



a naturally crystallised compound of alumina and silicic acid, may be obtained by the 
action of fluoride of silicon upon alternate layers of alumina and silica, heated to 
whiteness in a porcelain tube. The fluoride of silicon, acting upon the heated 
alumina, gives silicate of alumina and fluoride of aluminum — 

3A1 2 3 + 3SiF 4 = ~Al 2 3 .3Si0 2 + 2A1 2 F 6 , 

the newly-formed fluoride of aluminum, passing over a heated layer of silica, produces 
more silicate of alumina, regenerating fluoride of silicon — 

5Si0 2 + 2A1 2 F 6 = 2(Al 2 3 .Si0 2 ) + 3SiF 4 , 

so that a given quantity of the fluoride of silicon will convert an indefinite quantity 
of silica and alumina into the crystallised staurolite. It appears probable that other 
crystallised minerals have been formed in a similar manner, by the action of minute 
quantities of such agents of transformation, The frequent occurrence of minute 
quantities of fluorides in various minerals may thus have great significance. 

134. Hydrofluo-silicic acid or silica-fluoric acid (2HF.SiF 4 = 144 parts 
by weight). — This acid is only known in the form of a solution, which is 
obtained by passing fluoride of silicon into water — 

3SiF 4 + 2H 2 = 2(2KF.SiF 4 ) wrojiuo-siiicicacid) + Si0 2 . 

The gas must not be passed directly into the water, lest the separated 
silica should stop the orifice of the tube, to prevent which, the latter 
should dip into a little mercury at the bottom of the water, when eacli 
bubble, as it rises through the mercury into the water, will become sur- 
rounded with an envelope of gelatinous silica, and if the bubbles be very 
regular, they may even form tubes of silica extending through the whole 
height of the water. 

For preparing hydrofluo-silicic acid it will be found convenient to employ a gallon 
stoneware bottle (fig. 194), furnished with a wide tube dipping into a cup of mercury 
placed at the bottom of the water. 
1 lb. of finely powdered fluor spar, 
1 lb. of fine sand, and 64 measured 
ounces of oil of vitriol, are introduced 
into the bottle, which is gently heated 
upon a sand-bath, the gas being 
passed into about 5 pints of water. 
After 6 or 7 hours the water will 
have become pasty, from the separa- 
tion of gelatinous silica. It is poured 
upon a filter, and when the liquid 
has drained through as far as pos- 
sible, the filter is wrung in a cloth 
to extract the remainder of the acid 
solution, which will have a sp. gr. 
of about 1 -078. 

A dilute solution of hydrofluo- 
silicic acid may be concentrated 
by evaporation up to a certain 
point, when it begins to decom- 
pose, evolving fumes of fluoride 
of silicon, hydrofluoric acid re- 
maining in solution and volatilising in its turn if the heat be continued. 
Of course the solution corrodes glass and porcelain when evaporated in 
them. If the solution of hydrofluo-silicic acid be neutralised with potash, 
and stirred, a very characteristic crystalline precipitate of silico-fluoride of 
potassium is formed — 




194. 



-Preparation of hydrofluo-silicic 
acid. 



2HF.SiF 4 + 2KHO - 2K~F.SiF 4 (saico-ftwriJeof P ot«ssi 



urn) 



2H 2 



186 GENERAL REVIEW OF THE HALOGENS. 

But if an excess of potash be employed, a precipitate of gelatinous silica 
will be separated, fluoride of potassium remaining in the solution — 

2HF.SiF 4 + 6KHO = 6KF + 4H 2 + Si0 2 . 

One of the chief uses of hydrofluo-silicic acid is to separate the potash 
from its combination with certain acids, in order to obtain these in the 
separate state. 

135. Fluoride of boron (BF 3 ) may be prepared by a process similar to 
that employed for fluoride of silicon, but it is also obtained by strongly 
heating a mixture of powdered anhydrous boracic acid with twice its 
weight of fluor spar in an iron tube — 

3CaF 2 + B 2 3 = 3CaO + 2BF 3 . 

The fluoride of boron is a gas which fumes strongly in moist air like 
the fluoride of silicon. It is absorbed eagerly by water, w T ith evolution of 
heat. One volume of water is capable of dissolving 700 volumes of 
fluoride of boron, producing a corrosive heavy liquid (sp. gr. 1*77) which 
fumes in air, and chars organic substances on account of its attraction for 
water. This solution is known as fluoboric or borofluoric acid, and its 
formation is explained by the equation — 

2BF 3 + 3H 2 - B 2 3 .6HF {Fluoboric acid) . 

When the solution is heated, it evolves fluoride of boron until its 
specific gravity is reduced to 1'58, when it distils unchanged. 

Hydrofluoboric acid is obtained in solution by adding a large quantity 
of water to fluoboric acid — 

4(B 2 3 .6HF) = B 2 3 + 9H 2 + 6(HF.BF 3 ) {Hydrofluoboric acid) . 

This acid resembles the hydrofluo-silicic; its hydrogen may be ex- 
changed for metals to form borofluorides. 

136. General review of chlorine, bromine, iodine, and fluorine. — These 
four elements compose a natural group, the members of which are con- 
nected, by the similarity of their chemical properties, far more closely than 
those of any other group- of elements. They are usually styled the 
halogens, from their tendency to produce salts resembling sea-salt in their 
composition (aAs, the sea), and such salts are called haloid salts. These 
elements are also called salt-radicals, from their property of forming salts 
by direct union with the metals. Each of these elements combines with. 
an equal volume of hydrogen to form an acid which occupies the joint 
volumes of its constituents. 

The equivalent weights of these elements also represent their atomic 
weights, so that they are decidedly mon-atomic elements. 

The halogens also supply the most prominent example of the gradation 
in properties sometimes observed among the members of the same natural 
group of elements. 

In the order of their chemical energy, that is, of the force with which 
they hold other elements in chemical combination with them, fluorine 
should stand first, its combining energy being so great as to cause a serious 
difficulty in isolating it at all ; chlorine would rank next, then bromine, 
and iodine last. 

The atomic weights follow the inverse order of their chemical energies : 



OKES AND MINERALS CONTAINING SULPHUR. 187 

fluorine, 19 ; chlorine, 35*5 ; bromine, 80; iodine, 127 ; — numbers which, 
of course, also represent their relative specific gravities in the state of 
vapour. 

A similar gradation is observed in the physical state and colour of those 
three which are well known ; chlorine being a yellow gas, bromine a red 
liquid, boiling at 145° F., and iodine a black solid, boiling at 347° E. 

Even in the exceptions which occur to the order of chemical energy 
.above alluded to, the same progression is noticed ; thus fluorine has so 
little attraction for oxygen that no oxide is known, chlorine has less 
attraction for oxygen than bromine (chloric acid being less stable than 
bromic), whilst bromine has less than iodine, which is said to be capable 
even of uniting directly with ozonised oxygen to form iodic acid. 

The compounds of these elements with hydrogen are all gases distin- 
guished by a powerful attraction for moisture and great similarity of 
odour. 

Their potassium-salts all crystallise in the same (cubical) form. 

The fluoride of silver is deliquescent and soluble in water ; the chloride 
is insoluble in water, but dissolves very easily in ammonia ; the bromide 
dissolves with some difficulty in ammonia ; and the iodide is insoluble. 



SULPHUR 

S = 32 parts by weight = 1 volume (at 1900° F.) 
137. Sulphur is remarkable for its abundant occurrence in nature in 
the uncombined state, in many volcanic districts. It is also found, as 
sulphuretted hydrogen, in many mineral waters, and very abundantly in 
combination with metals, forming the numerous ores known as sulphurets 
or sulphides, of which the following are the most abundant : — 

Iron pyrites, Bisulphide of iron, FeS 2 

Copper pyrites, Sulphide of iron and copper, Cu 2 S.Fe 2 S 3 

Galena, Sulphide of lead, PbS 

Blende, Sulphide of zinc, ZnS 

Crude antimony, Sulphide of antimony, Sb 2 S 3 

Cinnabar, Sulphide of mercury, HgS . 

Sulphur is plentifully distributed also, in combination with oxygen and 
a metal, in the form of sulphates, of which the most conspicuous are : — 

Gypsum, Sulphate of lime, CaO.S0 3 .2H 2 

Heavy spar, Sulphate of baryta, BaO.S0 3 

Celestine, Sulphate of strontia, SrO. S0 3 

Epsom salts, Sulphate of magnesia, MgO.S0 3 .7H 2 

Glauber's salt, Sulphate of soda, Na 2 O.SO 3 .10H 2 O . 

In plants, sulphur is also found in the form of sulphates, and as a con- 
stituent of the vegetable albumen (of which it forms about 1-5 per cent.) 
piesent in the sap. It is also contained in certain of the essential oils 
remarkable for their peculiar pungent odour, such as — 

Essence of garlic, C fi H l0 S. 

Essence of mustard, C 4 H.NS. 

In animals, sulphur occurs as sulphates, as a constituent of albumen, 
fibrine, and caseine (in neither of which does it exceed 2 per cent.); and 
in bile, one of the products from which (taurine, C 2 H 7 NO a S) contains 25 
per cent, of sulphur. 

Eor our supplies of sulphur we are chiefly indebted to Sicily, where 
large quantities of it are found in ah uncombined state in beds of blue 



188 



EXTRACTION OF SULPHUR. 



clay. Magnificent crystalline masses of sulphate of strontia are often 
found associated with it ; the sulphur itself sometimes occurs in the 
form of transparent yellow octahedra, "but more frequently in opaque 
amorphous masses. The districts in which sulphur is found are usually 
volcanic, and those which border the Mediterranean are particularly rich 
in it. Sulphur has also been found in Iceland and California. 

The native sulphur being commonly distributed in veins through masses 
of gypsum and celestine, has to be separated from these by the action of 
heat. When the ores contain more than 12 per cent, of sulphur, the bulk 
of it is melted out, the ore being thrown into rough furnaces or cauldrons 
with a little fuel, and smothered up with, earth, so as to prevent the com- 
bustion of the sulphur, which runs down in the liquid state to the bottom of 
the cauldron, and is drawn out into wooden moulds.'* But when the propor- 
tion of sulphur is small, the ore is heated so as to convert the sulphur into 
vapour, which is condensed in another vessel. The operation is conducted 
in Sicily in rows of earthen jars (A, fig. 195), heated in a long furnace, 




sulphur. 

and provided with short lateral pipes, which convey the sulphur into 
similar jars (B) standing outside the furnace, in which the vapour of sul- 
phur condenses in the liquid state, and flows out into pails of water. The 
sulphur obtained by this process is imported as rough sulphur, and con- 




Fig. 196. — Sulphur refinery. 

tains 3 or 4 per cent, of earthy impurities. In order to separate these it 
is redistilled, in this country, in an iron retort (A, fig. 196), from which 

* High pressure steam has been applied with advantage for melting the sulphur out of 
the ores, which are enclosed in an iron v< 



SULPHUR DISTILLED FROM PYRITES. 



189 



the vapour is conducted into a large brick chamber (B), upon the sides of 
which it is deposited in the form of a pale yellow powder {flowers of sul- 
phur, or sublimed sulphur). When the operation has been continued for 
some time the walls of the chamber become sufficiently hot to melt the 
sulphur, which is allowed to collect, and afterwards cast in wooden 
moulds, forming roll sulphur or brimstone. Distilled sulphur is obtained 
by allowing the vapour to pass from the retort into a small receiving- 
vessel (C) cooled by water, where it condenses in the liquid state ; this 
variety of sulphur is preferred for the manufacture of gunpowder, for 
reasons which will be stated hereafter. 



Sulphur is readily distilled on a small scale in a Florence flask (fig. 197), another 
flask cut off at the neck (see p. 171) being employed 
as a receiver. The flask containing the sulphur 
should he supported upon a thin iron wire triangle, 
and heated by a gauze-burner, at first gently, and 
afterwards to the full heat. Flowers of sulphur 
will at first condense in the receiver, and will be 
followed by distilled sulphur when the temperature 
increases. A slight explosion of the mixture of 
sulphur vapour and air may take place at the com- 
mencement of the distillation. An ounce of sulphur 
may be distilled in a few minutes. 




Fig. 197. —Distillation of 
sulphur. 



We are by no means entirely dependent 
upon Sicily for sulphur, for this element can 
be easily extracted from iron and copper pyrites, both which are found 
abundantly in this country. 

Iron pyrites forms the yellow metallic-looking substance which is often 
met with in masses of coal, sometimes in distinct cubical crystals, and 
which is to be picked up in large quantities on some sea-beaches, where it 
occurs in rounded nodules, rusty outside, but having a fine radiated 
metallic fracture. When this mineral is strongly heated it gives up part 
of its sulphur ; at a very 
high temperature one 
half of the sulphur may 
be separated — 

FeS 2 = FeS + S 

but by an ordinary fur- 
nace heat only about 
one-fourth can be ob- 
tained. The distillation 
of iron pyrites is some- 
times effected in coni- 
cal fire-clay vessels (fig. 
198) closed at the wider 
end, and stopped to- 
wards the other with a 
perforated plate to allow 
the passage of the sul- 
phur vapour. Each vessel contains 100 lbs. of pyrites, and yields 14 lbs. 
of sulphur. 

The sulphur obtained in this way has a green colour, due to the pre- 
sence of a little sulphide of iron carried over mechanically during the 
distillation ; in order to purify it, it is melted and allowed to cool slowly, 




Fig. 198.— Furnace for distillation of sulphur 
from pyrites. 



190 ACTION OF HEAT UPON SULPHUR. 

when the sulphide of iron subsides ; the upper portion of the mass is then 
further purified by distillation. 

Sulphur may also be obtained from copper pyrites (Cu 2 S.Fe 2 S 3 ) in the 
process of roasting the ore previously to the extraction of the copper. 
The ore is heaped up into a pyramid, the base of which is about 30 feet 
square ; a layer of powdered ore is placed at the bottom to prevent too 
rapid access of air ; above this there is a layer of brushwood : a wooden 
chimney is placed in the centre, and is made to communicate with air- 
passages left between the faggots ; around this chimney the large frag- 
ments of the ore are piled to a height of about 8 feet, and a layer of 
powdered ore, about 12 inches deep, is strewn over the whole. The heap 
contains about 2000 tons of pyrites, and will yield 20 tons of sulphur. 
The fire, being kindled by dropping lighted faggots down the chimney, 
burns very slowly because of the limited access of air, and after a few 
days sulphur is seen to exude from the surface, and is received in cavities 
made for the purpose in different parts of the heap ; the roasting requires 
five or six months for its completion. In this operation a part of the 
sulphur has been separated by the mere action of heat, and another part 
has been displaced by the oxygen of the air, which has converted a portion 
of the iron into an oxide ; a part of the separated sulphur has been burnt, 
the rest having escaped combustion on account of the limited access of air. 

The sulphur extracted from pyrites is generally found to contain a little 
arsenic, which is frequently associated with those minerals. Immense 
quantities of sulphur are consumed in this country for the manufacture of 
sulphuric acid, gunpowder, lucifer matches, vulcanised caoutchouc, and 
for making the sulphurous acid employed in bleaching processes. 

Much sulphur has recently been extracted from the tank-waste of the 
alkali works, by a process which will be described in the manufacture of 
carbonate of soda. 

138. Properties of sulphur. — In its ordinary forms sulphur has a 
characteristic yellow colour, though milk of sulphur, or precipitated sul- 
phur (obtained by adding an acid to the solution of sulphur in an alkali), 
is white. It suffers electrical disturbance with remarkable facility, so 
that when powdered in a dry mortar it clings to it with great pertinacity. 
One of the most remarkable features of sulphur is its inflammability, 
due to its tendency to combine with oxygen at a moderately elevated 
temperature. It melts at a heat not much above the boiling point of 
water (239° F.), and inflames at about 500° F., 
burning with a pale blue flame, and emitting the 
well-known suffocating odour of sulphurous acid 
(SO,). 

The changes in the physical condition of this 
element under the influence of heat are very extra- 
ordinary. If a quantity of sulphur be introduced 
into a Florence flask and subjected to a gradually 
increasing heat (fig. 199), it is soon converted into 
a pale yellow limpid liquid (250° F), the colour 
of which becomes gradually brown as the heat 
rises, until, at about 350° F., it is nearly black and 
Fio . 199 opaque, and is so viscid that the flask may be 

inverted without spilling it ; at this point the 
temperature of the sulphur remains stationary for a time, notwithstand- 




ELECTEOPOSITIVE AND ELECTRONEGATIVE SULPHUR. 191 

ing that it is still over the flame, showing that heat is becoming latent in 
converting the sulphur into the new modification. On continuing the 
heat, the sulphur once more becomes liquid (500°), though not so mobile 
as at first, and at a much higher temperature (836° F.) it boils, and is 
converted into a brownish red very heavy vapour ; at this point of the 
experiment, an explosion of the mixture of sulphur vapour with air 
often takes place. The flask may now be removed from the flame, and 
a little of the sulphur poured into a vessel of water, through which 
it will descend in a continuous stream, forming a soft elastic string like 
india-rubber; the portion remaining in the flask will be observed, as 
it cools, to pass again through the same states, becoming viscid at 350° 
and very liquid at 250° ; another portion may now be poured into water, 
through which it will fall in isolated drops, solidifying into yellow brittle 
crystalline buttons of ordinary sulphur. As the portion of sulphur left 
in the flask cools, it will be found to deposit small tufts of crystals, and 
ultimately to solidify altogether to a yellow crystalline mass. 

The brown ductile sulphur, when kept for a few hours, will become yel- 
low and brittle, passing, in great measure, spontaneously into the crystalline 
sulphur. The change is accelerated by a gentle heat, and is attended with 
evolution of the heat which the sulphur was found to absorb at 350° F. 
Eoth these varieties of sulphur are, of course, insoluble in water, and they 
are not dissolved to any great extent by alcohol and ether. If the crystal- 
line variety be shaken with a little bisulphide of carbon it rapidly dis- 
solves, and on allowing the solution to evaporate spontaneously, it deposits 
beautiful octahedral crystals, resembling those of native sulphur (fig. 200). 
Ductile sulphur, however, is insoluble in bisulphide of carbon. 

When flowers of sulphur are shaken with bisulphide of carbon, a con- 
siderable quantity passes into solution, the remainder consisting of the 
amorphous, or insoluble sulphur. Eoll sulphur dissolves to a greater 
extent, and sometimes entirely, in the bisulphide, and distilled sulphur 
is always easily soluble. 

The soluble and insoluble forms of sulphur appear to represent distinct 
chemical varieties of the element. When a solution of sulphuretted hydro- 
gen (H 2 S) is decomposed by the galvanic battery, the hydrogen, as would 
be expected, is separated at the negative pole, and the sulphur at the 
positive pole (page 5). The sulphur, therefore", was the electronegative 
element of the compound. This sulphur is soluble in bisulphide of car- 
bon. When an acid is added to a solution of an alkaline sulphide con- 
taining more than one equivalent of sulphur, the excess of the latter is 
precipitated, and is then also found to be soluble in bisulphide of carbon, 
for it played an electronegative part towards the metal with which it was 
in combination. 

When sulphurous acid (S0 2 ) is decomposed by the battery, the sulphur 
is separated at the negative pole, showing that it played an electropositive 
part in the sulphurous acid. This electropositive sulphur is insoluble in 
bisulphide of carbon. The sulphur in the chloride of sulphur (S 2 C1 2 ) also 
plays an electropositive part, and accordingly, when this compound is 
decomposed by water, the sulphur which separates is insoluble in bisul- 
phide of carbon. The existence of these two forms of sulphur affords 
some support to the theory of the dual constitution of the elements noticed 
at page 52. 

The electropositive sulphur would be expected to manifest a greater 
attraction for oxygen than the electronegative variety, and accordingly, it 



192 



ALLOTROPIC FORMS OF SULPHUR. 




Fig. 200. 



is found to be far more easily oxidised by nitric acid. Electropositive or 

insoluble sulphur is converted into electronegative or soluble sulphur by 

the action of a moderate heat, itself evolving heat during the process of 

conversion. "When melted in contact with sulphurous acid, 

the soluble sulphur is converted externally into the insoluble 

form. 

Crystalline or soluble sulphur is capable of existing in 
two distinct forms. The natural form of crystallised sul- 
phur is the octahedron with a rhombic base (fig. 200), and 
this is the usual form which sulphur assumes when crystal- 
lised from its solutions. . But if sulphur be melted in a 
covered crucible, allowed to cool until the surface has con- 
gealed, and the remaining liquid portion poured out after 
piercing the crust (with two holes, one for admission of air), the crucible 
will be lined with beautiful needles which are oblique prisms (fig. 201). 
These crystals are brownish yellow, and transparent when freshly made ; 
but they soon become opaque yellow, and although they retain their 
prismatic appearance, they have now changed into minute 
rhombic octahedra, the change being attended with evolu- 
tion of heat. On the other hand, if a crystal of octahedral 
sulphur be exposed for a short time to a temperature of 
about 230° F. (in a boiling saturated solution of common 
salt, for example), it becomes opaque, in consequence of 
the formation of a number of minute prismatic crystals in 
the mass. 

The difference between these two forms of crystalline 
sulphur extends to their fusing-points and specific gravities ; 
the prismatic sulphur fusing at 248° F., and the octahedral 
sulphur at 239° F. ; the specific gravity of the prisms being 1*98, and 
that of the octahedra 2*05. 

Eoll sulphur, when freshly made, consists of a mass of oblique prismatic 
crystals, but after being kept for some time, it consists of octahedra, although 
the mass generally retains the specific gravity proper to the prismatic form. 
This change in the structure of the mass, taking place when its solid 
condition prevented the free movement of the particles, gives rise to a 
state of tension which may account for the extreme brittleness of roll sul- 
phur. If a stick of sulphur be held in the warm hand, it often splits, 
from unequal expansion. These peculiarities of sulphur deserve careful 
study, as helping to elucidate the spontaneous alterations in the structure 
of glass, iron, &c, under certain conditions. 

Flowers of sulphur do not present a crystalline structure, but consist of 
spherical granules composed of insoluble sulphur enclosing soluble sulphur. 
Hot oil of turpentine dissolves sulphur freely, and when the solution is 
allowed to stand, the crystals which are deposited whilst the solution is 
hot, have the prismatic form, but as it cools, octahedra are separated. 
The following table exhibits the chief allotropic forms of sulphur : — 




Fig. 201. 



Octahedral . . 
Electro negative 

Prismatic 

Ductile . . . 
Amorphous . . 
Electropositive . 



Sp. gr. 
2-05 



Fusing point. 
239° 

248° 

Becomes 
octahedral. 



Soluble in bisulphide of 

carbon. 
Soluble in bisulphide of 

carbon. 

Insoluble in bisulphide 
of carbon. 



SPECIFIC GRAVITY OF SULPHUR VAPOUR. 193 

The octahedral is by far the most stable of the three, and is the ultimate 
condition which the others assume. 

Other varieties of sulphur, such as a black and a red modification, have 
been described, but they are of minor importance. 

Sulphur is capable of entering into direct combination with several other 
elements. It unites with chlorine and with some of the metals, if finely 
divided, even at the ordinary temperature, and it is capable Of combining 
at a high temperature with all the non-metals except nitrogen, and with 
nearly all the metals. 

If a mixture of 2 parts of copper filings and 1 part of sulphur, or of equal weights of 
iron filings and sulphur, be heated in a Florence flask or a test-tube, the combination 
will be attended with vivid combustion. 

The so-called Lemery's volcano was made by mixing iron filings with two-thirds of 
their weight of powdered sulphur, and burying several pounds of the moist mixture 
in the earth, when the heat evolved by the rusting of part of the iron provoked the 
energetic combination of the remainder with the sulphur, and the consequent develop- 
ment of much steam.* 

Several metals may be made to burn in sulphur vapour, as in oxygen, by heating 
the sulphur in a Florence flask with a gauze burner so 
as to keep the flask constantly filled with the brown 
vapour. Potassium and sodium, introduced in deflagrat- 
ing spoons, take fire spontaneously in the vapour (fig. 
202). 

A coil of copper wire glows vividly in sulphur vapour, 
and becomes converted into a brittle mass of sulphide of 
copper. 




Sulphur dissolves, though slowly, in boiling 
concentrated nitric and sulphuric acids, being 
oxidised by the former into sulphuric, and by 
the latter into sulphurous acid. It is far more 
rapidly converted into sulphuric acid by a mix- 
ture of nitric acid and chlorate of potash. The 
alkalies dissolve sulphur when heated, yielding 
yellow or red solutions which contain hyposulphites of the alkalies and 
sulphides of their metals. 

There is a very general resemblance in composition between the com- 
pounds of sulphur and those of oxygen with the- same elements. 

139. Influence of temperature upon the specific gravity of gases and 
vapours. — The specific gravity of a gas or vapour being denned as its 
weight, compared with that of an equal volume of dry and pure air at the 
same temperature and pressure, it might be supposed that so long as the 
temperatures were equal, their actual thermometric value would not influ- 
ence the sjjecific gravity. Indeed, with those gases and vapours which 
are condensible with difficulty, this is actually the case. Thus, if equal 
volumes of oxygen and air be weighed, either at a low or a high tempera- 
ture, provided their temperatures are the same, their weights will always 
stand to each other in the ratio of 1*1057 : 1. 

But with many vapours it is found that if they be weighed at tempera- 
tures too nearly approaching to their condensing points, their specific 
gravities are much higher than they are found to be at higher tempera- 

* A mixture of 60 parts of fine iron filings, 2 of sal-ammoniac, and 1 of sulphur, made 
into a paste with water, is very useful for making the joints of iron tubes air-tight, for 
it sets into a hard cement, the iron combining with the sulphur. 

N 



194 SOURCES OF SULPHURETTED HYDROGEN. 

tures. Sulphur affords a very well-marked instance of this. It boils at 
836° F., and if its vapour he weighed at a temperature of 900° F., it is 
found to weigh 6-617 times as much as an equal volume of air at 900° F., 
so that it is 96 times as heavy as hydrogen, or 1 atom of sulphur would 
occupy J vol. But if the vapour of sulphur be weighed at 1900° F., it 
is found to weigh only 2 '23 times as much as an equal volume of air at 
the same temperature and pressure, so that it is only 32 times as heavy 
as hydrogen, and one atom of sulphur occupies 1 vol. 



Hydrosulphuric Acid. 
H 2 S = 34 parts by weight = 2 vols. 

140. Sulphuretted hydrogen, or hydrosulphuric acid, has been already 
mentioned as occurring in some mineral waters, as at Harrowgate. It is 
also found in the gases emanating from volcanoes, sometimes amounting 
to one-fourth of their volume. It is a product of the putrefaction of 
organic substances containing sulphur, and is one of the causes of the 
sickening smell of drains, &c. Eggs, which contain a considerable pro- 
portion of sulphur, evolve sulphuretted hydrogen as soon as they begin 
to change, and hence the association between this gas and the " smell of 
rotten eggs," The same smell is observed when a kettle boils over upon 
a coke or coal fire, the hydrogen liberated from the water combining with 
the sulphur present in the fuel. 

Hydrosulphuric acid is also found among the products of destructive 
distillation of organic substances containing sulphur ; it was mentioned 
among the products from coal, in which it is for the most part combined 
with the ammonia formed at the same time, producing hydrosulphate of 
ammonia. 

It may be produced, though not in large quantity, by the direct union 
of hydrogen with sulphur vapour at a high temperature, or by passing a 
mixture of sulphur vapour and steam through a tube filled with red-hot 
pumice stone (the latter encouraging the action by its porosity). Hydro- 
sulphuric acid is more readily formed by heating a damp mixture of sul- 
phur and wood charcoal, and may be obtained in large quantity by heating 
a mixture of equal weights of sulphur and tallow, the latter furnishing 
the hydrogen. 

Preparation of hydrosulphuric acid. — For use in the laboratory, where 
it is very largely employed in testing for and separating metals, hydro- 
sulphuric acid is generally prepared by decomposing sulphide of iron with 
diluted sulphuric acid — 

FeS + H 2 O.S0 3 - H 2 S + FeO.S0 3 . 

Sulphide Hydrosulphuric Sulphate of 

of iron. acid. iron. 

To obtain sulphide of iron, a mixture of 3 parts of iron filings with 2 parts of 
flowers of sulphur is thrown, by small portions at a time, into an earthen crucible 
(A, fig. 203), heated to redness in a charcoal fire, the crucible being covered after 
each portion has been added. The iron and sulphur combine with combustion, and 
when the whole of the mixture has been introduced, the crucible is allowed to cool, 
the mass of sulphide of iron broken out, and a few fragments of it are introduced 
into a bottle (fig. 204) provided with a funnel tube for the addition of the acid, and 
•a bent tube for conducting the gas through a small quantity of water, to remove any 
splashes of sulphate of iron. From the second bottle the gas is conducted by a glass 



PROPERTIES OF HYDROSULPHURIC ACID. 



195 




Fie. 203. 



tube with a caoutchouc joint, either down into a gas-bottle, or into water, or any 
other liquid upon which the gas 
is intended to act. The frag- 
ments of sulphide of iron should 
be covered with enough water to 
fill the gns-bottle to about one- 
third, and strong sulphuric acid 
added by degrees through the 
funnel, the bottle being shaken, 
until effervescence is observed. 
An excess of strong sulphuric 
acid stops the evolution of gas 
by precipitating a quantity of 
white anhydrous sulphate of 
iron, which coats the sulphide 
and defends it from the action 
of the acid. "When no more gas 
is required, the acid liquid 
should be at once poured away, 
leaving the fragments of sulphide 
of iron at the bottom of the 
bottle for a fresh operation. 
The liquid, if set aside, will 
deposit beautiful green crystals of copperas or sulphate of iron (FeO.S0 3 .7H 2 0). 

Since the sulphide of iron prepared as above generally contains a little metallic 
iron, the sulphuretted hydrogen is mixed with free 
hydrogen, which does not generally interfere with its 
uses. The pure gas may be prepared by heating sul- 
phide of antimony (crude antimony) in a flask with 
hydrochloric acid — 

Sb 2 S 3 + 6HC1 = 3H 2 S + 2SbCl 3 . 

Properties of hydrosulphuric acid. — This 
gas is at once distinguished from all others by 
its disgusting odour. It is one-fifth heavier 
than air (sp. gr. 1*1912). Its gaseous state is 
not permanent, but a pressure of 17 atmo- 
spheres is required to reduce it to a colourless 
liquid which congeals to a transparent solid at — 122° F. "Water absorbs 
about three times its volume of sulphuretted hydrogen at the ordinary 
temperature ; both the gas and its solution are feebly acid to blue litmus 
paper. The gas is very combustible, burning -with a blue flame like that 
of sulphur, and yielding, as the chief products, water and sulphurous 
acid — 




Fig. 204. —Preparation of 
hydrosulphuric acid. 



H 2 S 



+ 0, 



ELO 



sex 



a little hydrated sulphuric acid (H 2 O.S0 3 ) is also formed, and unless 
the supply of air is very good, some of the sulphur will be separated ; 
thus, if a taper be applied to a bottle filled with sulphuretted hydrogen, 
a good deal of sulphur will be deposited upon the sides. This combusti- 
bility of sulphuretted hydrogen is of the greatest importance in those 
processes of chemical manufacture in which this gas is evolved (as in the 
preparation of ammoniacal salts from gas liquors), enabling it to be dis- 
posed of in the furnace instead of becoming a nuisance to the neighbour- 
hood. The gas causes fainting when inhaled in large quantity, and 
appears much to depress the vital energy when breathed for any length of 
time even in a diluted state. 

When dissolved ia water, hydrosulphuric acid is slowly acted upon by 
the oxygen of the air, which, converts its hydrogen into water, and causes 
a white deposit of (electronegative or soluble) sulphur. 



■196 SOLUTION OF HYDROSULPHURIC ACID. 

This is a great drawback to the use of this indispensable chemical in the labor- 
atory, since the solution of hydrosulphuric acid is so soon rendered useless. To 
diminish it as far as possible, the solution should be made either with boiled water (free 
from dissolved air), or with water which has already been once charged with the gas 
and spoilt by keeping, for all the oxygen dissolved in this water will have been con- 
sumed by the former portion of gas. The gas should be passed through the water 
until, on closing the bottle with the hand and shaking violently, the pressure is 
found to act outwards, showing the water to be saturated with the gas. By closing 
the bottle with a greased stopper, and inverting it, the solution may be preserved 
for some weeks, even though occasionally opened for use. 

In preparing the solution of hydrosulphuric acid, a certain quantity of the gas 
always escapes absorption. To prevent this from becoming a nuisance, the bottle 
containing the water to be charged with gas may be covered with an air-tight 
caoutchouc cap having two tubes, through one of which passes the glass tube con- 
veying the gas down into the water, and through the other, a tube conducting the 
excess of gas either into a gas-burner, where it may be consumed, or into a solution 
of ammonia which will absorb it, forming the very useful hydrosulphate of am- 
monia. 

The hydrogen of the hydrosulphuric acid is oxidised immediately by 
nitrous acid (Nfi 3 ), the sulphur being separated, and a considerable quan- 
tity of nitrite of ammonia produced — 

N 2 3 + 6H 2 S = 2¥H 3 + 3H 2 + S 6 . 

Concentrated nitric acid also oxidises the hydrogen and a part of the 
sulphur, sulphate of ammonia (2JSTH3.H2O.SO3) being found in the solu-' 
tion, and a pasty mass of sulphur separated. Chlorine, bromine, and 
iodine at once appropriate its hydrogen and separate the sulphur. 

In its action upon the metals and their oxides, hydrosulphuric acid re- 
sembles hydrochloric and the other hydrogen acids. Many of the metals 
displace the hydrogen and form metallic sulphides. This usually requires 
the assistance of heat, but mercury and silver act upon the gas at the 
ordinary temperature. Thus, if sulphuretted hydrogen be collected over 
mercury, the surface of the latter becomes coated with a black film of 
sulphide of mercury; H 2 S + Hg 2 = H 2 + Hg,S. In a similar way the 
surface of silver is slowly tarnished when exposed to sulphuretted hydro- 
gen, its surface being covered with a black film of sulphide of silver. It 
is on this account that silver plate is so easily blackened by the air of 
towns, which is contaminated with sulphuretted hydrogen. An egg spoon 
is always blackened by the sulphur from the egg. Silver coins kept in 
the pocket with lucifer matches are blackened, from the formation of a 
little sulphide of silver. The original brightness of the coin may be re- 
stored by rubbing it with a solution of cyanide of potassium, which dis- 
solves the sulphide of silver. Friction with strong ammonia will also 
remove the tarnish, and its application is safer than that of the poisonous 
cyanide. 

When heated in the gas, several metals displace the hydrogen from it. 
Thus, potassium acts upon it in a corresponding manner to that in which 
it acts upon water — 

H 2 + K - KHO + H 

H 2 S + K = KHS ■ + H , 

forming hydrosulphate of potassium (KHS). 

Tin removes the whole of the sulphur from hydrosulphuric acid at a 
moderate heat ; Sn + H 2 S = H 2 + SnS. 

When hydrosulphuric acid acts upon a metallic oxide, it generally con- 
verts it into a sulphide corresponding to the oxide, whilst the hydrogen 



SULPHUR ACIDS, BASES, AND SALTS. 197 

and oxygen unite to form water. Oxide of lead in contact with the gas 
yields black sulphide of lead and water ; PbO + H 2 S = PbS + H 2 0. 
Even if the oxide of lead be combined with an acid, the same change is 
produced by hydrosulphuric acid ; and hence paper impregnated with a 
salt of lead is used as a test for the presence of this gas. Thus, if paper 
be spotted with a solution of nitrate (or acetate) of lead, it will indicate 
the presence of even minute quantities of sulphuretted hydrogen (in 
impure coal-gas, for example) by the brown colour imparted to the spots, 
the nitrate of lead being decomposed by the hydrosulphuric acid — 

PbO.N 2 5 (Nitrate of lead) + H 2 S = II 2 0.]Sr 2 5 (Nitric acid) + PbS. 

It is in this manner that paints containing white lead (carbonate of 
lead) are darkened by exposure to the air of towns. Cards glazed with 
white lead, and engravings on paper whitened with that substance, sutler 
a similar change. Paintings, whether in oil .or water colours, in which 
lead is an ingredient, are also injured by air containing sulphuretted 
hydrogen. The interesting observation has recently been made that such 
colours, damaged by the formation of sulphide of lead, are restored by the 
continued action of light and air, the black sulphide of lead becoming 
oxidised and converted into the white sulphate of lead, PbS + 4 = 
PbO.S0 3 . In the dark this restoration does not take place, so that it is 
often a mistake to screen pictures from the light by a curtain. 

The action of hydrosulphuric acid upon the chlorides and other haloid 
salts of the metals generally resembles its action upon the oxides of the 
same metals. m 

Most of the sulphides of the metals, like the corresponding oxides, are 
insoluble in water, but many of the sulphides are also insoluble in diluted 
acids and in alkalies, so that when hydrosulphuric acid is brought into 
contact with the solutions of metals, it will often precipitate the metal in 
the form of a sulphide having some characteristic colour or other property 
by which the metal may be identified. 

Any solution of lead will give a black precipitate with solution of hydrosulphuric 
acid, the sulphide of lead being insoluble in diluted acids and in alkalies. 

A solution of antimony (tartar- emetic, for example, the tartrate of antimony and 
potash) mixed with an excess of hydrochloric acid, gives an orange-colonred preci- 
pitate (Sb 2 S 3 ) on adding hydrosulphuric acid ; but if^another portion be mixed with 
an excess of potash before adding the hydrosulphuric acid, there will be no precipi- 
tate, for the sulphide of antimony is soluble in alkalies. 

Chloride of cadmium gives a brilliant yellow precipitate of sulphide of cadmium on 
adding hydrosulphuric acid. 

Sulphate of zinc yields a white precipitate of sulphide of zinc (ZnS), but if a little 
hydrochloric acid be previously added, no precipitate is formed, the sulphide of zinc 
being soluble in acids. On neutralising the hydrochloric acid with ammonia, the 
sulphide of zinc is at once precipitated. 

It is evident that, in a solution containing cadmium and zinc, the metals may be 
separated by acidifying the liquid with hydrochloric acid, and adding excess of 
hydrosulphuric acid, which precipitates the sulphide of cadmium only. On filtering 
the solution, and adding ammonia, the sulphide of zinc is precipitated. 

Sulphur-acids and sulphur-bases. — Those sulphides which are soluble 
in the alkalies are often designated sulphur-acids, whilst the sulphides of 
the alkali-metals are sulphur-bases. These two classes of sulphides com- 
bine to form sulphur-salts analogous in composition to the oxygen-salts of 
the same metals. Thus, there have been crystallised, the salts 
Sulphostannate of (sulphide of) sodium, 2JSTa 2 S.SnS 2 
Sulphantimoniate „ . ,, 3Na 2 S.Sb 2 S 5 

Sulpharseniate ,, „ 3JN"a 3 S.A3 2 S 5 . 



198 PERSULPHIDE OF HYDROGEN. 

The sulphostannic (SnS 2 ), sulphantimonic (Sb 2 S 5 ), and sulpharsenic 
(As 2 S 5 ) acids respectively, corresponding to stannic (Sn0 2 ), antimonic 
(Sb 2 5 ), and arsenic (As 2 5 ) acids. 

The action of air upon the sulphides of the metals is often turned to 
account in chemical manufactures. At the ordinary temperature, the 
sulphides of those metals which form alkaline oxides (such as sodium and 
calcium), when exposed to the air in the presence of water, yield, first, 
mixtures of the oxide and bisulphide, 2JSTa 2 S + = ]STa 2 + ISTa 2 S 2 ; 
and afterwards the hyposulphite, Na 2 S 2 + 3 = Na 2 S 2 3 . This change is 
sometimes turned to account for the manufacture of hyposulphite of soda. 

When the metal forms a less powerful base with oxygen, the sulphide 
is often converted into sulphate by exposure to moist air ; thus, CuS + 
4 = CuO.S0 3 , which is taken advantage of for the separation of copper 
from tin ores. 

The black sulphide of iron (FeS), when exposed to moist air, becomes 
converted into red peroxide of iron, with separation of sulphur — 

2FeS + 3 = Fe 2 3 4- S 2 , 
a change which enables the gas manufacturer to revive, by the action of 
air, the peroxide of iron employed for removing the sulphuretted hydrogen 
from coal gas. 

When roasted in air at a high temperature, the sulphides correspond- 
ing to the more powerful bases are converted into sulphates ; thus 
ZnS + 4 = ZnO.S0 3 , which explains the production of sulphate of 
zinc by roasting blende. But in most cases part of the sulphur is con- 
verted into sulphurous acid at the same time. Subsulphide of copper, 
for instance, is partly converted into oxide of copper by roasting, Cu 2 S + 
4 = 2CuO + S0 2 , a change of great importance in the extraction of 
copper from its ores. 

141. Persulphide of. hydrogen. — The composition of this substance is not yet satis- 
factorily ascertained. The similarity of its chemical properties to those of binoxide 
of hydrogen prompts the wish that its formula may be H 2 S 2 . Some analyses, how- 
ever, seem to lead to the formula H 2 S 5 , but since tne persulphide is a liquid capable 
of dissolving free sulphur, which is not easily separated from it, there is much diffi- 
culty in determining the exact proportion of this element with which the hydrogen 
is combined. 

"When equal weights of slaked lime and sulphur are boiled with water, an orange- 
coloured liquid is formed, which contains hyposulphite of lime, bisulphide of calcium, 
and pentasulphide of calcium (CaS 5 ) — 

3CaO + S 6 = CaS 2 3 {Hyposulphite, of lime) + 2CaS 2 {Bisulphide of calcium). 

When hydrochloric acid is added to the filtered solution, an abundant precipitation 
of sulphur occurs, and much hydrosulphuric acid is evolved — 
CaS 2 + 2HC1 = CaCl 2 + H 2 S + S . 

But if the solution be poured by degrees into a slightly warm mixture of hydro- 
chloric acid with twice its bulk of water, and constantly stirred, a yellow heavy oily 
liquid collects at the bottom, which is the persulphide of hydrogen — 

CaS 2 + 2HC1 = H 2 S 2 (?) + CaCl 2 . 
The acid having been kept in excess, the persulphide has been preserved from the 
decomposition which it suffered in the presence of the alkaline solution in the 
former experiment. For the persulphide of hydrogen very closely resembles the per- 
oxide in the facility with which it may be decomposed into hydrosulphuric acid and 
sulphur ; it undergoes spontaneous decomposition even in sealed tubes, and the hydro- 
sulphuric acid then becomes liquefied by its own pressure. Most of the substances, 
the contact of which promotes the decomposition of the peroxide of hydrogen, have 
the same effect upon the persulphide. This compound has a peculiar odour which 
appears to affect the eyes ; of course, its vapour is mixed with that of hydrosul- 
phuric acid resulting from its decomposition. 



PREPARATION OF SULPHUROUS ACID. ] 99 

Oxides of Sulphur. 

142. Only two compounds of sulphur with oxygen have been obtained 
in the separate state, viz., sulphurous acid (S0 2 ) and sulphuric acid(S0. 3 ). 

Sulphurous Acid. 
S0 2 = 64 parts by weight = 2 vols. 

143. In nature, sulphurous acid is but rarely met with ; it exists in the 
gases issuing from volcanoes. Although constantly discharged into the 
air of towns by the combustion of coal (containing sulphur), it is so easily 
oxidised and converted into sulphuric acid, that no considerable quantity 
is ever found in the atmosphere. Sulphurous acid has been already men- 
tioned as the sole product of the combustion of sulphur in dry air and 
oxygen, but it is generally prepared for chemical purposes by removing 
part of the oxygen from sulphuric acid, which is easily effected by heating 
it with metallic copper — 

2(H 2 O.S0 3 ) + Cu = CuO.S0 3 + 2H 2 + S0 2 . 

Hydiat acid? 1PllUriC Sulphate of copper. 

300 grains of copper clippings are heated in a Florence flask with 4 oz. (measured) 
of strong sulphuric acid, the gas being conducted by a bent tube down to the bottom 
of a dry bottle closed with a perforated card (see fig. 177, p. 153). Some time will 
elapse before the gas is evolved, for sulphuric acid acts upon copper only at a high 
temperature ; but when the evolution of gas fairly commences, it will proceed very 
rapidly, so that it is necessary to remove the flame from under the flask. The 
gas will contain a little suspended vapour of sulphuric acid, wbich renders it turbid. 

When the operation is finished, and the flask has been allowed to cool, it will be 
found to contain a grey crystalline powder at the bottom of a brown liquid. The 
latter is the excess of sulphuric acid employed, and retains very little copper, since 
sulphate of copper is insoluble in strong sulphuric acid. If the liquid be poured off", 
and the flask filled up with water, and set aside for some time, the crystalline powder 
will dissolve, forming a blue solution of sulphate of copper, yielding that salt in fine 
prismatic crystals by evaporation and cooling. The dark powder remaining 
undissolved after extracting the whole of the sulphate of copper consists chiefly of 
sulphide of copper, the production of which is interesting, as showing how far the 
deoxidising effect of the copper may be carried in this experiment. 

Sulphurous acid is a very heavy (sp. gr. 2 # 25) colourless gas, characterised 
by its odour of burning brimstone. It condenses to a clear liquid at 0° F. 
(the temperature of a mixture of ice and salt) even at the ordinary pressure 
of the air, and has been frozen to a colourless crystalline solid at — 105° F. 

The liquefaction of the gas is easily exhibited by passing it down to the bottom of 
a tube (A, fig. 205) closed at one end, and surrounded with a mixture of pounded 
ice with half its weight of salt. The tube should have 
been previously drawn out to a narrow neck at B, 
which may afterwards be sealed by the blowpipe, the 
lower part of the tube being still surrounded by the 
freezing mixture, since the liquid sulphurous acid 
boils at 14° F. The tube need not be very strong, 
for at the ordinary temperature the vapour of sulphurous 
acid exerts a pressure of only 2 '5 atmospheres. Liquid 
sulphurous acid is a convenient agent for producing (by 
its rapid evaporation) the low temperature ( — 39° F.) 
required to effect the solidification of mercury. A 
small globule of this metal may readily be frozen by 
dropping some liquid sulphurous acid upon it in a 
watch-glass placed in a strong draught of air. The 
tube containing the sulphurous acid should be held in 
a woollen cloth or glove. The attractive experiment 
of freezing water in a red-hot crucible may also be Fig. 205. 

made with the liquid acid. A platinum crucible 
being heated to redness, and some liquid sulphurous acid poured into it, the liquid 




200 BLEACHING BY SULPHUROUS ACID. 

becomes surrounded with an atmosphere of sulphurous acid gas, which prevents its 
contact with the metal (assumes the spheroidal state), and its temperature is reduced 
by its own evaporation to so low a degree that a few drops of water allowed to flow 
into it will at once become converted into ice. 

Sulphurous acid gas is very easily absorbed by water, as may be shown 
by pouring a little water into a bottle of the gas, closing the bottle with 
the palm of the hand, and shaking it violently (see fig. 165, p. 145), 
when the diminished pressure due to the absorption of the gas will cause 
the bottle to be sustained against the hand by the pressure of the 
atmosphere. Water absorbs 43-5 times its bulk of the gas at the ordi- 
nary temperature. If the solution be exposed to a low temperature, a 
crystallised hydrate of sulphurous acid is obtained, the composition of 
which does not appear to be accurately settled. When the solution of 
sulphurous acid is kept for some time in a bottle containing air, its smell 
gradually disappears, the acid absorbing oxygen and becoming converted 
into sulphuric acid. 

Sulphurous acid, like carbonic acid, possesses in a high degree the 
power of extinguishing flame. A taper is at once extinguished in a 
bottle of the gas, even when containing a considerable proportion of air. 
One of the best methods of extinguishing burning soot in a chimney 
consists in passing up sidphurous acid by burning a few ounces of 
sulphur in a pan placed over the fire. 

The principal uses of sulphurous acid depend upon its property of 
bleaching many animal and vegetable colouring matters. Although a 
far less powerful bleaching agent than chlorine, it is preferred for bleach- 
ing silk, straw, wool, sponge, isinglass, baskets, &c, which would be 
injured by the great chemical energy of chlorine. The articles to be 
bleached are moistened with water and suspended in a chamber in which 
sulphurous acid is produced by the combustion of sulphur. The colour- 
ing matters do not appear in general to be decomposed by the acid, but 
rather to form colourless combinations with it, for in course of time, 
the original colour often reappears, as is seen in straw, flannel, &c, which 
become yellow from age, the sulphurous acid probably being oxidised 
into sulphuric acid. Stains of fruit and port wine on linen are con- 
veniently removed by solution of sulphurous acid. 

The red solution obtained by boiling a few chips of logwood with river water (dis- 
tilled water does not give so fine a colour), serves to illustrate the bleaching proper- 
ties of sulphurous acid. A few drops of the solution of the acid will at once change 
the red colour of the solution to a light yellow, but that the colouring power is sus- 
pended and not destroyed, may be shown by dividing the yellow liquid into two 
parts, and adding to them, respectively, potash and diluted sulphuric acid, which 
will restore the colour in a modified form. To contrast 
this with the complete decomposition of the colouring 
matter, a little sulphurous acid may be added to a weak 
solution of the permanganate of potash, when the splendid 
red solution at once becomes perfectly colourless, and 
neither acid nor alkali can effect its restoration, for in this 
case the red permanganic acid (Mn 2 7 ), supposed to exist 
in the permanganate of potash, is. reduced to the state of 
protoxide of manganese. 

If a bunch of damp coloured flowers be suspended in a 
bell -jar over a crucible containing a little burning sulphur 
(fig. 206), many of the flowers will be completely bleached 
by the sulphurous acid, and by plunging them afterwards 
into diluted sulphuric acid and ammonia, their colours 
Fig. 206. may be partly restored, with some very curious modifications. 

Another very useful property of sulphurous acid is that of arresting 




SULPHITES. 



201 




Fig. 207. 



fermentation (or putrefaction), apparently by killing the vegetable or 
animal growth, which is the cause of the fermentation. This is commonly 
designated the antiseptic property of sulphurous acid, and is turned to 
account when casks for wine or beer 
are sulphured in order to prevent the 
action of any substance contained in the 
pores of the wood, and capable of ex- 
citing fermentation, upon the fresh liquor 
to be introduced. If a little solution of 
sugar be fermented with yeast in a flask 
provided with a funnel tube (fig. 207), 
a solution of sulphurous acid poured in 
through the latter will at once arrest the fer- 
mentation. The salts of sulphurous acid 
(sulphites) are also occasionally used to 
arrest fermentation, in the manufacture of 
sugar, for instance. Clothes are sometimes fumigated with sulphurous 
acid to destroy vermin, and the air of rooms is disinfected by burning- 
sulphur in it. 

The disposition of sulphurous acid to absorb oxygen and pass into sul- 
phuric acid, renders it a powerful deoxidising or reducing agent. Solu- 
tions of silver and gold are reduced to the metallic state by sulphurous 
acid if a very little ammonia be added, and a gentle heat applied. 

If a solution of sulphurous acid be heated for some time in a sealed tube to 340° F. 
one portion of the acid deoxidises another, sulphur is separated, and sulphuric acid 
formed ; 3S0 2 + 2H 2 = 2(H 2 O.S0 3 ) + S. 

Sulphurous acid gas combines with ammonia gas to form two solid compounds, 
(NH 3 ) 2 S0 2 , and NH 3 .S0 2 , which are quite different in their properties from the 
sulphite and bisulphite of ammonia, which are formed when sulphurous acid acts 
upon solution of ammonia. 

Chlorine combines with an equal volume of sulphurous acid, under the influence 
of bright sunshine, to produce a colourless liquid, the vapour of which is very acrid 
and irritating to the eyes. Its composition is represented by S0 2 C1 2 , and it is some- 
times called chlorosulphuric acid, though it does not combine with bases, and is de- 
composed by water, yielding hydrochloric and sulphuric acids. It is also known as 
chloride of sulphuryle, S0 2 , being looked upon as the radical of sulphuric acid. The 
chloride of thionyle* SOCl 2 , is a colourless volatile liquid obtained by the action of 
hypochlorous acid gas on sulphur dissolved in the subchloride of sulphur. It is 
decomposed by water, yielding hydrochloric and sulphurous acids. 

Potassium and sodium, when heated in sulphurous acid, burn vividly, producing 
the oxides and sulphides of the metals. 

Iron, lead, tin, and zinc are also converted into oxides and sulphides when heated 
in sulphurous acid ; S0 2 + Zn 3 = ZnS + 2ZnO. 

Sulphites. — The acid character of sulphurous acid is rather feeble, 
although stronger than that of carbonic acid. There is much general 
resemblance between the sulphites and carbonates, in point of solubility, 
the sulphites of the alkali-metals being the only salts of sulphurous acid 
which are freely soluble in water. Sulphurous acid, like carbonic, forms 
two classes of salts, the sulphites (for example, sulphite of soda, ]STa 2 O.S0 2 ) 
and bisulphites (as bisulphite of potash, K 2 O.H 2 0.2S0 2 ). 

The sulphite of soda is extensively manufactured for the use of the 
papermaker, who employs it as an antiehlore for Trilling the hleach, that 
is, neutralising the excess of chlorine after bleaching the rags with chlo- 
ride of lime and sulphuric acid (see p. 152) — 

!Na 2 O.S0 2 + H 2 + Cl 2 = ¥a 2 O.S0 3 + 2HC1. 

* Qe'iov, sulpJmr. 



202 



SULPHUEIC ACID. 



It is prepared by passing sulphurous acid over damp crystals of car- 
bonate of soda, when the carbonic acid is expelled, and sulphite of soda 
formed, which is dissolved in water and crystallised. It forms oblique 
prisms having the composition ]STa 2 O.S0 2 .7Aq, which effloresce in the air, 
becoming opaque, and slowly absorbing oxygen, passing into sulphate of 
soda £Na 2 O.S0 3 ). Its solution is slightly alkaline to test-papers. 

For the manufacture of sulphite of soda, the sulphurous acid is obtained 
either by the combustion of sulphur or by heating sulphuric acid with 
charcoal — 

2(H 2 O.S0 3 ) + C = 2H 2 + C0 2 + 2S0 2 . 

The carbonic acid, of course, will not interfere with this application of 
the sulphurous acid. 

Just as in the case of carbonic acid (see p. 83), many chemists deny the 
acid nature of the compound S0 2 altogether, and term it sulphurous 
anhydride, reserving the name of sulphurous acid for the hydrated sul- 
phurous acid, H 2 O.S0 2 or H 2 S0 3 , obtained by exposing the aqueous solu- 
tion of sulphurous acid to a very low temperature. 



Sulphuric Acid. 

SO 3 = 80 parts by weight. 

144. It has been already noticed that one of the most abundant forms 
in which sulphur occurs in nature is that of sulphuric acid in combina- 
tion with certain bases. Hydrated sulphuric acid has also been found in 
certain springs and rivers in volcanic regions. Sulphurous acid and 
oxygen gases combine to form sulphuric acid (S0 3 ) when passed through 
a tube containing heated platinum or certain metallic oxides, such as those 
of copper and chromium, the action of which in promoting the combina- 
tion is not thoroughly understood. 

The combination may be shown by passing oxygen from the tube A (fig. 208) 
connected with a gas-holder, through a strong solution of sulphurous acid (B), so 

that it may take up a quantity of that gas, 
afterwards through a tube (C) containing 
pumice stone soaked with oil of vitriol, to 
remove the water, and then through a bulb 
(D) containing platinised asbestos (see p. 
138). The mixture of the gases issuing 
into the air is quite invisible, but when the 
bulb is gently heated, combination takes 
place, and dense white clouds are formed 
in the air, from the combination of the 
anhydrous sulphuric acid (SO s ) produced 
with the atmospheric moisture. 

An easier method of obtaining the 

anhydrous sulphuric acid will be 

noticed hereafter, but the hydrated acid is of so much more importance 

that its preparation and properties should be studied before those of the 

anhydrous acid. 

Hydrated sulphuric acid (H 2 O.S0 3 = 98 parts by weight). — More than 
four centuries ago, the alchemist Basil Valentine subjected green vitriol, 
as it was then called (sulphate of iron), to distillation, and obtained an 
acid liquid which he named oil of vitriol. The process discovered by this 
laborious monk is even now in use at IS r ordhausen in Saxony, and the 
Nordhausen oil of vitriol is an important article of commerce. The crys- 
tals of sulphate of iron (FeO.S0 3 .7H. 2 0) are exposed to the air so that 




Fig. 208. 



MANUFACTURE OF OIL OF VITRIOL. 203 

they may absorb oxygen, and become converted into the basic persul- 
phate of iron — 

2(FeO.S0 3 ) + = Fe 2 3 .2S0 3 . 

This salt is dried, and distilled in earthen retorts, the oil of vitriol 
being condensed in receivers of glass or stoneware. The action of heat 
upon the basic persulphate of iron separates the acid from the base, and 
if the salt were absolutely dry, the anhydrous sulphuric acid would be 
expected to distil over. There is always enough water, however, left in 
the persulphate, to combine with the anhydrous acid to form the Nord- 
hausen oil of vitriol, the composition of which is pretty correctly ex- 
pressed by the formula H. 2 0.2S0 3 . The peroxide of iron (Fe 2 3 ) which 
is left in the retorts, is the red powder known as colcothar, which is used 
for polishing plate glass and metals. 

The green vitriol employed for preparing the Nordhausen acid is obtained from 
iron pyrites (FeS 2 ). A particular variety of this mineral, white pyrites (or efflores- 
cent pyrites), when exposed to moist air, undergoes oxidation, yielding sulphate of 
iron and sulphuric acid — 

FeS 2 + H 2 + 7 = FeO.S0 3 + H 2 O.S0 3 . 

Large masses of this variety of pyrites in mineralogical cabinets may often be 
seen broken up into small fragments, and covered with an acid efflorescence of sul- 
phate of iron from this cause. Ordinary iron pyrites is not oxidised by exposure to 
the air unless it be first subjected to distillation in order to separate a portion of the 
sulphur which it contains. 

The Nordhausen acid is readily distinguished from English sulphuric 
acid by its fuming in the air when the bottle is opened. This is due to 
the escape of a little vapour of anhydrous sulphuric acid. It is heavier 
than the English acid, its specific gravity being 1 -9. It is chiefly used 
for dissolving indigo in preparing the Saxony blue dye, and is a con- 
venient source of the anhydrous sulphuric acid ; for if it be gently heated 
in a retort, the anhydrous acid is disengaged, and may be condensed in 
silky crystals in a receiver kept cool by ice, whilst ordinary hydrated sul- 
phuric acid (H 2 O.S0 3 ) is left in the retort. 

The process adopted at JSTordhausen, though simple in theory, is expen- 
sive on account of the consumption of fuel and the breaking of the retorts, 
so that the price of the acid, compared with that of English manufacture, 
is very high. 

The first step towards the discovery of our present process was also 
made by Valentine, when he prepared his oleum sulphur is per campanum, 
by burning sulphur under a bell-glass over water, and evaporating the acid 
liquid thus obtained. The same experimenter also made a very important 
advance when he burnt a mixture of sulphur, sulphide of antimony, and 
nitre, under a bell-glass placed over water ; but it was not until the middle 
of the eighteenth century that it was suggested by some French chemists 
to burn the sulphur and nitre alone over water, a process by which the 
acid appears actually to have been manufactured upon a pretty large scale. 
The substitution of large chambers of lead for glass vessels by Dr Roebuck 
was a great improvement in the process, and about the year 1770 the 
preparation of the acid formed an important branch of manufacture ; since 
then the process has been steadily improving, until, at the present time, 
upwards of 100,000 tons are annually consumed in Great Britain, and a 
very large quantity is exported. The diminution in the price of oil of 
vitriol w^ell exhibits the progress of improvement in its production, for 



204 THEORY OF PRODUCTION OF OIL OF VITRIOL. 

the original oil of sulphur appears to have been sold for about half a 
crown an ounce, and that prepared by burning sulphur with nitre in glass 
vessels at the same price per pound • but when leaden chambers were 
introduced, the price fell to a shilling per pound, and at present oil of 
vitriol can be purchased at the rate of five farthings per pound. 

The description of the present process of manufacture will be best 
understood after a consideration of the chemical changes upon which it 
depends. 

It has been seen that when sulphur is burnt in air, sulphurous acid is 
the chief product. When sulphurous acid acts upon hydrated nitric acid, 
in the presence of water, sulphuric acid and nitric oxide are formed — 
3S0 2 + H 2 O.N 2 5 + 2H 2 = 3(H 2 O.S0 3 ) + 2NO. 

Nitric oxide, in contact with air, combines with its oxygen to form 
nitric peroxide (NQ 2 ). 

If nitric peroxide is brought into contact with sulphurous acid and 
water, it is again converted into nitric oxide with formation of sulphuric 
acid — 

N0 2 + S0 2 + H 2 = NO + H 2 O.S0 3 . 

It appears, therefore, that nitric oxide may be employed to absorb 
oxygen from the air, and to convey it to the sulphurous acid, so that 
theoretically, an unlimited quantity of sulphurous acid, supplied with air 
and water, might be converted into sulphuric acid by a given quantity of 
nitric oxide. 

To illustrate these important chemical principles of the ?nanufacture of sulphuric 
acid, the following experiments may he performed : — 

I. A quart bottle of nitric oxide (p. 137) is placed mouth to mouth with a pint 
bottle of oxygen, when both bottles will be filled with the red nitric peroxide. 

II. The quart bottle of this red gas is placed mouth to mouth with a quart bottle 
of sulphurous acid gas (fig. 209), when the red colour will soon disappear, and the 

sides of the bottles will be covered with a crystalline 
substance formed by the reaction between the nitric 
peroxide, the sulphurous acid, and the small quantity 
of water present in the gases. The true composition 
of this crystalline body is doubtful, but if, for the 
purpose of the present reasoning, it be regarded as 
2(IS T O.S0 3 ).H 2 O, its formation would be represented 
• by the equation — 




III. A little water is shaken round the insides of 
the bottles, when the crystalline compound will be 
decomposed with effervescence, evolving nitric oxide, 
and producing hydrated sulphuric acid — 

Fig. 209. 2(NO.S0 3 ).H 2 + H 2 = 2NO + 2(H 2 O.S0 3 ). 

IV. Air* is blown into the bottles through a glass tube, when the presence of the 
nitric oxide will be proved by the formation of the red nitric peroxide. 

In the presence of abundance of water this crystalline compound is not produced, 
as may be shown by the following modification of the experiment. 

V. A large glass flask or globe (A, fig. 210) is fitted with a cork, through which 
are passed — 

(a) a tube connected with a flask (D) containing copper and strong sulphuric acid, 
for evolving sulphurous acid ; 

(b) a tube connected with a flask (B) containing copper and diluted nitric acid (sp. 
gr. 1 *2) for supplying nitric oxide ; 

(c) a tube proceeding from a small flask (E) containing water. 

* The operation is of course more striking if oxygen is employed instead of air, the 
globe being filled with oxygen by displacement at the commencement. 






REACTIONS IN THE VITRIOL CHAMBERS. 



205 




Fig. 210. — Preparation of sulphuric acid. 



On applying a gentle heat to the flask containing nitric acid and copper, the nitric 
oxide passes into & the globe and combines with the oxygen of the air, filling the 
globe with red nitric peroxide. 
The nitric oxide flask may then 
be removed. Sulphuric acid is 
then generated by heating the 
flask containing sulphuric acid 
and copper ; the sulphurous acid 
will soon decolorise the red nitric 
peroxide, the contents of the 
globe becoming colourless, and 
the crystalline compound form- 
ing abundantly on the sides ; the 
sulphurous acid flask may then 
be removed. Steam is sent into 
the globe from the flask contain- 
ing water, when the crystalline 
compound will be dissolved, and 
sulphuric acid will collect at the 
bottom of the globe. If air be 
now blown into the globe, the 
nitric oxide will again acquire 
the red colour of nitric peroxide. 

If the experiment be repeated, the steam being introduced simultaneously with 
the sulphurous acid, no crystalline compound whatever will be formed, the sulphurous 
acid being at once converted into hydrated sulphuric acid. 

Since the cork is somewhat corroded in this experiment, it is preferable to have 
the mouth of the flask ground and closed by a ground glass plate, perforated with 
holes for the passage of the tubes. The perforations are easily made by placing the 
glass plate flat against the wall and piercing it with the point of a revolving rat's- 
tail file dipped in turpentine ; the file is then gradually worked through the hole 
until the latter is of the required size. 

The process employed for the manufacture of English oil of vitriol will 
now be easily understood. 

A series of chambers is constructed of leaden plates, the edges of 
which are united by autogenous soldering (that is, by fusing their edges, 
without solder, which would be rapidly corroded by the acid vapours) ; 
the leaden chambers are supported and strengthened by a framework of 
timber (fig. 211). 

The sulphurous acid is generated by burning sulphur or iron pyrites in 
a suitable furnace (A) adjoining the chambers, and so arranged that the 
sulphurous acid produced may be mixed with about the proper quantity 
of air to furnish the oxygen required for its conversion into sulphuric 
acid. 

Nitric acid vapour is evolved from a mixture of nitrate of soda and oil 
of vitriol (see p. 131) contained in an iron pan which is heated by the 
combustion of the sulphur, so that the nitric acid is carried into the cham- 
bers with the current of sulphurous acid and air. 

Water covers the floor of the chambers to the depth of about two inches, 
and jets of steam are introduced at different parts from an adjacent 
boiler (B). 

The sulphurous acid acts upon the nitric acid vapour, in the presence 
of the water, forming nitric oxide and hydrated sulphuric acid, which 
rains down into the water on the floor of the chambers — 

3S0 2 + H 2 O.N" 2 5 + 2H 2 = 2^0 + 3(H 2 O.S0 3 ). 

If this nitric oxide were permitted to escape from the chambers, and a 
fresh quantity of nitric acid vapour introduced to oxidise another portion 
of sulphurous acid, it is evident that 2 molecules (170 parts by weight) of 



206 



PLAN FOR ECONOMISING NITRIC OXIDE. 



nitrate of soda would be required to furnish the nitric acid for the con- 
version of 3 atoms (96 parts by weight) of sulphur, whereas, in practice, 
6 parts by weight only of nitrate of soda are employed for 96 parts of 
sulphur. 

For the nitric oxide (NO) at once acquires oxygen from the air ad- 
mitted together with the sulphurous acid, and becomes nitric peroxide 
(N0 2 ), which oxidises more sulphurous acid in the presence of water, 
converting it into hydrated sulphuric acid — 



2S0 o + 2NO, 



2H 2 



2NO. 



2(HO.S0 3 ) 

A great reduction in the volume of the gas in the chamber thus takes 
place (4 vols. S0 2 and 4 vols. N0 2 yielding 4 vols. NO), so that there 




Fig. 211. — Sulphuric acid chambers. 

is room for the. introduction of a fresh quantity of the mixture of sul- 
phurous acid and air from the furnace, upon which thenitric oxide acts 
as before, taking up the oxygen from the air and handing it over to the 
sulphurous acid, in the presence of water, to produce a fresh supply of 
hydrated sulphuric acid. 

But the nitrogen of the air takes no part in these changes, and since 
the oxygen consumed in converting the sulphur into sulphuric acid is 
accompanied by four times its volume of nitrogen, a very large accumula- 



COMMERCIAL VARIETIES OF SULPHURIC ACID. 207 

tion of this gas takes place in the chambers, and provision must be made 
for its removal in order to allow space for those gases which take part in 
the change. The obvious plan would ajDpear to be the erection of a simple 
chimney for the escape of the nitrogen at the opposite end of the chamber 
to that at which the sulphurous acid and air enter it ; and this plan was 
formerly adopted, but the nitrogen carries off with it a portion of the 
nitric oxide which is so valuable in the chamber, and to save this the 
escaping nitrogen is now generally passed through a leaden chamber (C) 
filled with coke, over which oil of vitriol is allowed to trickle ; the oil of 
vitriol absorbs the nitric oxide, and flows into a cistern (D), from which 
it is pumped up to the top of another chamber (E) filled with coke, or 
arranged with shelves in cascade, through which the hot sulphurous acid 
and air are made to pass as they enter, when they take up the nitric oxide 
from the oil of vitriol, and carry it with them into the chamber. 

Before the introduction of this plan of retaining the nitric oxide by oil 
of vitriol, it required a quantity of nitrate of soda amounting to Jth or 
y^th of the weight of the sulphur to convert it into sulphuric acid, whereas 
about i^th or even less is now often made to suffice. 

The sulphuric acid is allowed to collect on the floor of the chamber 
until it has a specific gravity of about 1*6, and contains 70 percent, of oil 
of vitriol (H 2 O.S0 3 ). If it were allowed to become more concentrated 
than this, it would absorb some of the nitric oxide in the chamber, so 
that it is now drawn off. 

This acid is quite strong enough for some of the applications of sul- 
phuric acid, particularly for that which consumes the largest quantity in 
this country, viz., the conversion of common salt into sulphate of soda as 
a preliminary step in the manufacture of carbonate of soda. To save the 
expense of transporting the acid for this purpose, the vitriol chambers 
form part of the plant of the alkali works. 

To convert this weak acid into the ordinary oil of vitriol of commerce, 
it is run off into shallow leaden pans set in brickwork, and supported on 
iron bars over the flue of a furnace, where it is heated until so much 
water has evaporated that the specific gravity of the acid has increased to 
1*72. The concentration cannot be carried further in leaden pans, 
because the strong acid acts upon the lead, and converts it into sulphate — 

2(H 2 O.S0 3 ) + Pb = PbO.S0 3 + 2H 2 + S0 2 . 

The acid of 1 '72 sp. gr. contains about 80 per cent, of true oil of vitriol 
(H 2 O.S0 3 ), and is largely employed for making superphosphate of lime, 
and in other rough chemical manufactures. It is technically called or own 
acid, having acquired a brown colour from organic matter accidentally 
present in it. 

To convert this brown acid into commercial oil of vitriol, it is boiled 
down, either in glass retorts or platinum stills, when water distils over, 
accompanied by a little sulphuric acid, and the acid in the retort becomes 
colourless, the brown carbonaceous matter being oxidised by the strong 
sulphuric acid, with formation of carbonic and sulphurous acids. When 
dense white fumes of oil of vitriol begin to pass over, showing that all 
the superfluous water has been expelled, the acid is drawn off by a 
siphon. 

The very diluted acid which distils off is employed instead of water on 
the floor of the leaden chamber. 



208 ACTION OF SULPHURIC ACID ON ORGANIC MATTERS. 

The cost of the acid is very much increased by this concentration. It cannot be 
conducted in open vessels, partly on account of the loss of sulphuric acid, partly be- 
cause concentrated sulphuric acid absorbs moisture from the open air even at the 
boiling point. The loss by breakage of the glass retorts is very considerable, although 
it is reduced as far as possible by heating them in sand, and keeping them always at 
about the same temperature by supplying them with hot acid. But the boiling 
point of the concentrated acid is very high (640° F. ), and the retorts consequently 
become so hot that a current of cold air or an accidental splash of acid will frequently 
crack them at once. Moreover the acid boils with succussion or violent bumping, 
caused by sudden bursts of vapour, which endanger the safety of the retort. 

With platinum stills the risk of fracture is avoided, and the distillation may be 
conducted more rapidly, the brown acid (sp. gr. 1 72) being admitted at the top, 
and the oil of vitriol (sp. gr. 1 # 84) drawn off by a platinum siphon from the bottom 
of the still, which is protected from the open fire by an iron jacket. But since a 
platinum still will cost £2000 or £3000, the interest upon its value increases the 
cost of production of the acid. 

When the perfectly pure acid is required, it is actually distilled over so as to leave 
the solid impurities (sulphate of lead, &c.,) behind in the retort. Some fragments 
of rock crystal should be introduced into the retort to moderate the bursts of vapour, 
and heat applied by a ring gas-burner with somewhat divergent jets. 

Divested of working details, this most important chemical manufacture 
may be thus described : — 

A mixture of sulphurous acid, air, steam, and a little vapour of nitric 
acid, is introduced into a leaden chamber containing a layer of water. 
The nitric acid is reduced by the sulphurous acid to the state of nitric 
oxide (NO), which takes up oxygen from the air (forming N0 2 ), and 
gives it to the sulphurous acid, which it converts into sulphuric acid. 
This is absorbed by the water, forming diluted sulphuric acid, which is 
concentrated by evaporation, first in leaden pans, and afterwards in 
glass retorts or platinum stills. 

Properties of oil of vitriol. — The properties of concentrated sulphuric 
acid are very characteristic. Its great weight (sp. gr. 1'842), freedom 
from odour, and • oily appearance, distinguish it from any other liquid 
commonly met with, which is fortunate, because it is difficult to preserve 
a label upon the bottles of this powerfully corrosive acid. Although, if 
absolutely pure, it is perfectly colourless, the ordinary acid used in the 
laboratory has a peculiar grey colour, due to traces of organic matter. Its 
high boiling-point (640° F.) has been already noticed ; and although its 
vapour is perfectly transparent in the vessel in which the acid is boiled, 
as soon as it issues into the air it condenses into voluminous dense clouds 
of a most irritating description. Even a drop of the acid evaporated in 
an open dish will fill a large space with these clouds. Oil of vitriol 
solidifies when cooled to about - 30° F., but the acid once solidified re- 
quires a much higher temperature to liquefy it again. Oil of vitriol 
rapidly corrodes the skin and other organic textures upon which it falls, 
usually charring or blackening them at the same time. Poured upon a 
piece of wood, the latter speedily assumes a dark brown colour ; and if a 
few lumps of sugar be dissolved in a very little water, and stirred with 
oil of vitriol, a violent action takes place, and a semi-solid black mass is 
produced. This property of sulphuric acid is turned to account in the 
manufacture of blacking, in which treacle and oil of vitriol are employed. 
These effects are to be ascribed to the powerful attraction of oil of vitriol 
for water. Woody fibre (C 6 H 10 O 5 ) (which composes the bulk of wood, 
paper, and linen), and sugar, (C 12 H 22 O n ), may be regarded, for the pur- 
pose of this explanation, as composed of carbon associated with 5 and 11 



ACTION OF SULPHURIC ACID ON METALS. 



209 



tending 



to remove the water would 



molecules of water, and any cause 
tend to eliminate tlie^ carbon. 

The great attraction of this acid for water is shown by the high tempe- 
rature (often exceeding the boiling point of water) produced on mixing 
oil of vitriol with water, which renders it necessary to be careful in dilut- 
ing the acid. 

The water should be placed in a jug, and the oil of vitriol poured into it in a thin 
stream, a glass rod being used to mix the acid Avith the water as it flows in. Ordi- 
nary oil of vitriol becomes turbid when mixed with water, from the separation of 
sulphate of lead (formed from the evaporating pans), which is soluble in the concen- 
trated but not in the diluted acid, so that if the latter be allowed to stand for a few 
hours, the sulphate of lead settles to the bottom, and the clear acid may be poured 
off free from lead. Diluted sulphuric acid has a smaller bulk than is occupied by 
the acid and water before mixing. 

Even when largely diluted, sulphuric acid corrodes textile fabrics very 
rapidly, and though the acid be too dilute to appear to injure them at 
first, it will be found that the water evaporates by degrees, leaving the 
acid in a more concentrated state, and the fibre is then perfectly rotten. 
The same result ensues at once on the application of heat ; thus, if charac- 
ters be written on paper with the diluted acid, they will remain invisible 
until the paper is held to the fire, when the acid will char the paper, and 
the writing will appear intensely black. 

If oil of vitriol be left exposed to the air in an open vessel, it very soon 
increases largely in bulk from the absorption of water, and a flat dish of 
oil of vitriol under a glass shade (fig. 212) is frequently employed in the 
laboratory for drying substances with- 
out the assistance of heat. The drying 
is of course much accelerated by plac- 
ing the dish on the plate of an air- 
pump, and exhausting the air from 
the shade, so as to effect the drying 
in vacuo. It will be remembered 
also that oil of vitriol is in constant 
use for drying gases. 

At a red heat, the vapour of oil 
of vitriol is decomposed into water, 
sulphurous acid, and oxygen — 

H 2 O.S0 3 = H 2 + S0 2 + 0. 

This decomposition takes place most easily when the vapour is passed 
through a strongly heated tube of platinum, and it has been taken advan- 
tage of for the preparation of oxygen, the sulphurous acid being absorbed 
by passing the mixed gases through lime. Keflecting upon the manufac- 
ture of oil of vitriol, it will be perceived that the oxygen thus obtained 
was originally derived from the air. 

When sulphur is boiled with oil of vitriol, the latter gradually dissolves 
the melted sulphur, converting it into sulphurous acid — 
S + 2(H 2 O.S(X) =± 3S0 2 + 2H 2 0. 

All ordinary metals are acted upon by concentrated sulphuric acid when 
heated, except gold and platinum (this last even does not quite escape 
when long boiled with the acid), the metal being oxidised by one portion 
of the acid, which is thus converted into sulphurous acid, the oxide com- 
bining with another part of the sulphuric acid to form a sulphate. Thus, 

o 




Fig. 212."— Drying over oil of vitriol. 



210 SULPHUlUw ANHYDRIDE. 

when silver is "boiled with, strong sulphuric acid, it is converted into sul- 
phate of silver, which is soluble in hot water — 

Ag 2 + 2(H 2 O.S0 3 ) = Ag 2 O.S0 3 + 2H 2 + S0 2 . 

Should the silver contain any gold, it is left behind in the form of a dark 
powder. Sulphuric acid is extensively employed for the separation or 
parting of silver and gold. This acid is also employed for extracting gold 
from copper ; and when sulphate of copper is manufactured by dissolving 
that metal in sulphuric acid (see p. 199), large quantities of gold are 
sometimes extracted from the accumulated residue left undissolved by the 
acid. If the sulphuric acid contains nitric acid, it dissolves a considerable 
quantity of gold, which separates again in the form of a purple powder 
when the acid is diluted with water, the sulphate of gold formed being 
reduced by the nitrous acid when the solution is diluted. 

Some of the uses of sulphuric acid depend upon its specific action on 
certain organic substances, the nature of which has not yet been clearly 
explained. Of this kind is the conversion of paper into vegetable parch- 
ment by immersion in a cool mixture of two measures of oil of vitriol and 
one measure of water, and subsequent washing. The conversion is not 
attended by any change in the weight of the paper. 

Beside oil of vitriol, sulphuric acid forms other definite combinations 
with water. By evaporating diluted sulphuric acid in vacuo at 212° F., 
an acid is left which has the composition H 2 Q.S0 3 .2H 2 (sp. gr. 1*63). 
If this acid be evaporated in air at 400° F., as long as steam escapes, the 
remaining acid has the composition H 2 O.S0 3 .H 2 (sp. gr. 1-78). This 
acid is called glacial sulphuric acid, because it solidifies to a mass of ice- 
like crystals at 47° F. 

145. Anhydrous sulphuric acid or sulphuric anhydride. — The mode of 
preparing this substance from the fuming sulphuric acid has already been 
noticed. It is more commonly obtained by expelling the water from bi- 
sulphate of soda (Na 2 O.H 2 0.2S0 3 ) by fusing it at a dull red heat, and 
afterwards distilling the anhydrous bisulphate (JSTa 2 0.2S0 3 ) in an earthen 
retort, when neutral sulphate of soda (Na 2 O.S0 3 ) is left, and the anhydrous 
sulphuric acid passing off as vapour may be condensed in a receiver cooled 
by ice. 

Anhydrous sulphuric acid forms a white mass of crystals resembling 
asbestos ; it fumes when exposed to air, since it emits vapour which con- 
denses the moisture of the air, and it soon deliquesces from absorption of 
water, becoming hydrated sulphuric acid. When thrown into water it 
hisses like red-hot iron, from the sudden formation of steam. It fuses at 
65° F., and boils at 110° F. The vapour is decomposed, as mentioned 
above, into sulphurous acid and oxygen, when passed through a red-hot 
tube. Phosphorus burns in its vapour, combining with the oxygen and 
liberating sulphur. Baryta glows when heated in the vapour of anhydrous 
sulphuric acid, and combines with it to form sulphate of baryta. 

Anhydrous sulphuric acid is capable of combining with olefiant gas 
(C 2 HJ and oil-gas (C 4 H 8 ), and absorbs these from mixtures of gases. 
In the analysis of coal-gas, a fragment of coke wetted with JSTordhausen 
sulphuric acid is passed up into a measured volume of the gas standing 
over mercury, to absorb these illuminating hydrocarbons. 

An interesting method of obtaining the anhydrous sulphuric acid con- 
sists in pouring 2 parts by weight of oil of vitriol over 3 parts of anhydrous 



SULPHATES. 211 

phosphoric acid, contained in a retort cooled in ice and salt, and after- 
wards distilling at a gentle heat, when the phosphoric acid retains the 
water, and the anhydrous sulphuric acid may be condensed in a cooled 
receiver. 

Determination of the composition of sulphuric acid and oil of vitriol. — When 32 
grains (one atomic weight) of sulphur are oxidised by boiling with nitric acid, the 
excess of nitric acid expelled by a moderate heat, the remaining hydrated sulphuric 
acid mixed with an excess of pure oxide of lead of known weight, say 300 grains, 
and all the water expelled by a high temperature, the mixture of sulphate and oxide 
of lead which is left is found to weigh 380 grains, showing that 32 parts of sulphur 
have combined with oxygen from the nitric acid to form 80 grains of sulphuric acid. 
Hence the sulphuric acid contains 32 grains of sulphur and 48 grains of oxygen, cor- 
responding to the formula S0 3 . 

The vapour of S0 3 is found to be 43 times as heavy as hydrogen, which would give 86 
for its molecular weight (p. 36). By treating a known weight of oil of vitriol with an 
excess of oxide of lead, and expelling the water by heat, it is found that 80 grains of 
S0 3 are combined with 18 grains of water. Hence oil of vitriol contains H 2 O.S0 3 . 
Its vapour, therefore, should be 49 times as heavy as hydrogen ; but experiment 
shows it to be only 24 times as heavy (at 880° F.) ; this appears to be due to the 
temporary decomposition (or dissociation) of the two volumes of oil of vitriol into two 
volumes of water and two volumes of sulphuric acid. This deprives us of the usual 
evidence as to the molecular weight of a compound. 

On examining the behaviour of oil of vitriol with caustic potash or soda, it is 
found that two salts of each alkali may be obtained, a sulphate and a bisulphate ; 
thus the sulphate of potash is K 2 O.S0 3 , or K 2 S0 4 , and the bisulphate is K 2 O.H 2 0, 
2S0 3 or KHO.S0 3 , or KHS0 4 , showing that the hydrogen can be replaced by halves, 
and that therefore at least two atoms of hydrogen must be contained in the molecule 
of oil of vitriol. The presence of these two atoms of hydrogen replaceable by a 
metal is implied by saying that the oil of vitriol is a dibasic or bibasic acid. 

146. Sulphates. Action of sulphuric acid upon metallic oxides. — At 
common temperatures sulphuric acid has a more' powerful attraction for 
bases than any other acid, and is therefore capable of displacing all other 
acids from their salts ; many cases will be remembered in which this power 
of sulphuric acid is turned to ace ount. 

So great is the acid energy of sulphuric acid, that when it is allowed 
to act upon an indifferent or acid metallic oxide, it causes the separation 
of a part of the oxygen, and combines with the basic oxide so produced. 
Advantage is sometimes taken of this circumstance for the preparation of 
oxygen ; for instance, when binoxide of manganese is heated with sul- 
phuric acid, sulphate of manganese is produced, and oxygen disengaged. 

Mn0 2 + H 2 O.S0 3 - MnO.S0 3 + O + H 2 0. 

Again, if chromic acid be treated in the same way, sulphate of sesquioxide 
of chromium will be produced, with liberation of oxygen — 

2Cr0 3 + 3(H 2 O.S0 3 ) = Cr 2 3 .3S0 3 + 3 + 3H 2 . 

A mixture of bichromate of potash (K 2 0.2Cr0 3 ) and sulphuric acid is 
sometimes used as a source of oxygen. 

Many bases are capable of forming two salts with sulphuric acid, a 
neutral sulphate and an acid sulphate. The acid sulphates may be repre- 
sented as compounds of the neutral sulphates with hydrated sulphuric 
acid; thus, the neutral sulphate of potash is K 2 O.S0 3 , and the bisulphate 
is K 2 O.S0 3 , H 2 O.S0 3 . The latter, being a solid salt which possesses, at 
high temperatures, almost all the acid energy of sulphuric acid, is most 
useful in blowpipe and metallurgic experiments. When strongly heated, 
this salt parts with hydrated sulphuric acid, and neutral sulphate of pot- 
ash is left. It has been seen that bisulphate of soda (Na 2 O.SO,, H 2 O.S0 3 ) 



212 



SULPHATES. 



parts with its water when heated, and becomes ]STa 2 0.2S0 3 . Crystals 
of anhydrous bisulphate of potash K 2 0.2S0 3 have also been obtained. 

Sulphuric acid forms a large number of double salts in which two sul- 
phates are combined together. The large class of alums yields examples 
of these, in which one of the sulphates contains an alkaline base, and the 
other a basic sesquioxide. Potash-alum, for example, is represented by 
the formula K. 2 O.S0 3 ,Al 2 3 .3SO a .24Aq, being a double sulphate of alu- 
mina and potash. 

The following table exhibits the composition of the sulphates most 
frequently met with : — 



Chemical Name. 



Sulphate of potash 
Sulphate of soda 
Bisulphate of potash 
Sulphate of am- 
monia 
Sulphate of baryta 
Sulphate of lime 
Sulphate of mag- 
nesia 
Double sulphate 
of alumina and 
potash 
Double sulphate 
of alumina and 
ammonia 
Double sulphate "> 
of chromium .V 
and potash ) 

Sulphate of iron 

Sulphate of man- 
ganese 
Sulphate of zinc 
Sulphate of lead 
Sulphate of copper 



Common Name. 



Sal polychrest 
Glauber's Salt 



Heavy spar 
Gypsum 
Epsom salts 

Potash- alum 



Ammonia- j 
alum \ 

Chrome- 
alum 

Green vitriol 
Copperas 



White vitriol 

Blue vitriol 1 
Blue stone | 



Additive Formula. 



BaO.S0 3 

CaO.S0 3 .2H 2 

MgO.S0 3 .7H 2 



2NH„.H o 0.S0 Q 



K 2 O.S0 3 , 



MnO.SO,.5H 2 
ZnO.S0 3 .7H 2 



PbO.SO, 



Substitutive Formula. 



K 2 S0 4 

Na 2 SO 4 .10H 2 O 

KHS0 4 

(NH 4 ) 2 S0 4 

BaS0 4 
CaS0 4 .2H 2 

MgS0 4 .7H 2 
KA12S0 4 .12H 2 

NH 4 A12S0 4 .12H 2 

KCr2S0 4 .12H 2 

FeS0 4 .7H 2 

MnS0 4 .5H 2 

ZnS0 4 .7H 2 
PbS0 4 

CuS0 4 .5H a O 



In consequence of the tendency of sulphuric acid to break up into sul- 
phurous acid and oxygen at a high temperature, most of the sulphates are 
decomposed by heat ; sulphate of copper, for example, when very strongly 
heated, leaves oxide of copper, whilst sulphurous acid and oxygen escape; 
CuO.S0 3 = CuO + S0 2 + 0. Sulphate of iron is more easily decom- 
posed, because of the attraction of the protoxide of iron for the oxygen, 
with which it combines to form sesquioxide — 



2(FeO.S0 3 ) = 



Fe 2 0, 



+ SO, + SO, 



part of the acid escaping in the anhydrous state. 

Sulphate of zinc (ZnO.S0 3 ) has been proposed as a source of oxygen 
upon the large scale, since it is a very cheap salt, and when strongly 
heated, yields a residue of oxide of zinc which is useful as a white paint, 
whilst sulphurous acid and oxygen gases escape, the former of which may 



HYPOSULPHITE OF SODA. 213 

be absorbed by lime or soda, yielding sulphites which are useful in the 
arts. 

The neutral sulphates of potash, soda, baryta, strontia, lime, and oxide 
of lead are not decomposed by heat, and sulphate of magnesia is only 
partly decomposed at a very high temperature. 

When a sulphate is heated with charcoal, the carbon removes the whole 
of the oxygen, and a sulphide of the metal remains, thus — 

K 2 O.S0 3 (.Sulphate of potash) + C, = K 2 S (Sulphide of potassium) 4. 4CO . 

Hydrogen, at a high temperature, effects a similar decomposition. 

Even at the ordinary temperature, sulphate of lime in solution is some- 
times deoxidised by organic matter ■ this may occasionally be noticed in 
well and river waters when kept in closed vessels ; they acquire a strong 
smell of hydrosulphuric acid, in consequence of the conversion of a part 
of the sulphate of lime into sulphide of calcium by the organic consti- 
tuents of the water, and the subsequent decomposition of the sulphide of 
calcium by the carbonic acid present in the water. 

147. Hyposulphurous acid* — This acid has not been obtained either 
in the anhydrous state or in combination with water ; but as many salts 
are known which contain, in addition to a metallic oxide, sulphur and 
oxygen in the proportions expressed by the formula S 2 2 , many chemists 
assume the existence of hyposulphurous acid, having that composition, in 
such salts, which are therefore called hyposulphites. 

The hyposulphite of soda is by far the most important of these salts, 
being very largely employed in photography, and as a substitute for 
sulphite of soda as an antichlore. The simplest method of preparing it 
consists in digesting powdered roll sulphur with solution of sulphite of 
soda (JSTa 2 O.S0 2 ), when the latter dissolves an atom of sulphur and becomes 
hyposulphite of soda (]STa 2 O.S 2 2 or !N"a 2 S 2 3 ), which crystallises from the 
solution, when sufficiently evaporated, in fine prismatic crystals, having 
the formula Na 2 S 2 3 .5H 2 0. 

On a large scale, the hyposulphite of soda is more economically prepared 
from the hyposulphite of lime obtained by exposing the refuse (tank-waste 
or soda-waste) of the alkali-works to the air for some days. This refuse 
contains a large proportion of sulphide of calcium, which becomes con- 
verted into hyposulphite of lime by oxidation — 

2CaS + 4 = CaS 2 3 + CaO . 

The hyposulphite of lime is dissolved out by water, and the solution 
mixed with carbonate of soda, when carbonate of lime is precipitated, 
and hyposulphite of soda remains in solution — 

CaS 2 3 + Na 2 O.C0 2 - CaO.C0 2 + Na 2 S 2 3 . 

The most remarkable and useful property of the hyposulphite of soda is 
that of dissolving the chloride and iodide of silver, which are insoluble in 
water and most other liquids. 

On mixing a solution of nitrate of silver with one of chloride of sodium, a white 
precipitate of chloride of silver is obtained, the separation of which is much promoted 
t>y stirring the liquid ; AglST0 3 + Nad == AgCl + NalSTOg. The precipitate may 
be allowed to settle and washed twice or thrice by decantation. One portion of the 
chloride of silver is transferred to another glass, mixed with water, and solution of 
hyposulphite of soda added by degrees. The chloride of silver is very easily dis- 
solved, yielding an intensely sweet solution, which contains the hyposulphite of 

* 'Tiro, under, containing less oxygen than sulphurous acid. 



214 HYPOSULPHITE OF SODA. 

.silver, produced by double decomposition between the chloride of silver and hypo 
sulphite of soda — 

2AgCl + Na 2 S 2 3 = 2N"aCl + Ag 2 S 2 3 

Chloride of Hyposulphite of Chloride of Hyposulphite of 

silver. soda. sodium. silver. 

The hyposulphite of silver combines with the excess of hyposulphite of soda to 
form the double salt Ag 2 S 2 3 .2(]Sra 2 S 2 Q 3 ), which may be obtained in extremely 
sweet crystals from the solution. 

If the other portion of the chloride of silver be exposed to the action of light, and 
especially of direct sunlight, it assumes by degrees a dark slate colour, from the for- 
mation of subchloride of silver, chlorine being set free ; 2AgCl — Ag 2 Cl + CI. By 
treating this darkened chloride of silver with hyposulphite of soda, as before, the un- 
altered chloride of silver will be entirely dissolved, but the subchloride will be decom- 
posed into chloride of silver, which dissolves in the hyposulphite, and metallic silver, 
which is left in a very finely divided state as a black powder ; Ag 2 Cl = AgCl + Ag. 
The application of these facts in photography is well illustrated by the following 
experiments. A sheet of paper is soaked for a minute or two in a solution of 10 
grains of common salt in an ounce of water contained in a fiat dish. It is then 
dried, and soaked for three minutes in a solution of 50 grains of nitrate of silver in 
an ounce of water. The paper thus becomes impregnated with chloride of silver 
formed by the decomposition between the chloride of sodium and the nitrate of 
silver. It is now hung up in a dark place to dry. If a piece of lace, or a fern leaf, 
or an engraving on thin paper, with well-marked contrast of light and shade, be 
laid upon a sheet of the prepared paper, pressed down upon it by a plate of glass, 
and exposed for a short time to sunlight, a perfect representation of the object will 
be obtained, those parts of the sensitive paper to which the light had access having 
been darkened by the formation of subchloride of silver, whilst those parts which 
were protected from the light remain unchanged. 

But if this photographic print were again exposed to the action of light, it would 
soon be obliterated, the unaltered chloride of silver in the white parts being acted 
on by light in its turn. The print is therefore fixed, by soaking it for a short time 
in a saturated solution of hyposulphite of soda, which dissolves the white unaltered 
chloride of silver entirely, and decomposes the subchloride formed by the action of 
light, leaving the black finely-divided metallic silver in the paper. The print should 
now be washed for tvvo or three hours in a gentle stream of water, to remove all the 
hyposulphite of silver, when it will be quite jjermanent. 

The power of hyposulphite of soda to dissolve chloride of silver has 
also been turned to account for extracting that metal from its ores, in 
which it is occasionally present in the form of chloride. 

The behaviour of solution of hyposulphite of soda with powerful acids 
explains the circumstance that the hyposulphurous acid has not been 
isolated, for if the solution be mixed with a little diluted sulphuric or 
hydrochloric acid, it remains clear for a few seconds, and then becomes 
suddenly turbid from the separation of sulphur, at the same time evolving 
a powerful odour of sulphurous acid; S 2 2 = S + S0 2 . This disposi 
tion of the hyposulphurous acid to break up into sulphurous acid and 
sulphur also explains the precipitation of metallic sulphides, which often 
takes place when hyposulphite of soda is added to the acid solutions of 
the metals. Thus if an acid solution of chloride of antimony (obtained 
by boiling crude antimony ore (Sb 2 S 3 ) with hydrochloric acid) be added to 
a boiling solution of hyposulphite of soda, the sulphur separated from the 
hyposulphurous acid combines with the antimony to form a fine orange- 
red precipitate of sulphide of antimony (Sb 2 S ;j ), which is used in painting 
under the name of antimony vermilion. On the large scale the solution of 
hyposulphite of lime obtained from the alkali waste is employed in the pre- 
paration of antimony vermilion, as being less expensive than the soda- 
salt. 

Instead of adding sulphur to sulphurous acid, hyposulphurous acid in 



DITHIONIC ACID. 215 

combination may be obtained by removing oxygen from the former acid. 
Thus if an aqueous solution of sulphurous acid be acted on by zinc, one 
portion of the acid is deoxidised and converted into hyposulphurous acid, 
which combines with the oxide of zinc — 

3S0 2 + Zn 2 = ZnO.S0 2 + ZnS 2 3 . 

The presence of hyposulphite in the solution may be proved by adding 
hydrochloric acid. 

When crystals of hyposulphite of soda are heated in the air, they first 
fuse in their water of crystallisation, then dry up to a white mass, which 
burns with a blue flatne, leaving a residue of sulphate of soda. If heated 
out of contact with air, pentasulphide of sodium will be left with the sul- 
phate of soda — 

4(Na 2 S 2 3 5H 2 0) - 20H 2 O + 3(1^0.80,) + Na 2 S 5 . 

Some of the reactions of hyposulphite of soda become more intelligible 
when the salt is represented as sulphate of soda (Na 2 S0 4 ) in which an 
atom of sulphur has displaced an atom of oxygen (Na 2 S0 3 S). 

148. Hyposulphuric acid or dithionic acid (H 2 S 2 6 ) has not at present acquired 
any practical importance, and has not been obtained in the anhydrous state. To 
prepare a solution of the acid, binoxide of manganese in a state of fine division is 
suspended in water and exposed to a current of sulphurous acid gas, the water being 
kept very cold whilst the gas is passing. A solution of hyposulphate of manganese 
is thus obtained ; 2S0 2 + Mn0 2 = MnS 2 6 . Some sulphate of manganese is always 
formed at the same time ; S0 2 + Mn0 2 = MnO.S0 3 , and if the temperature be 
allowed to rise, this will he produced in large quantity. 

The solution containing sulphate and hyposulphate of manganese is decomposed 
by solution of baryta (baryta- water), when the oxide of • manganese is precipitated, 
together with sulphate of baryta, and hyposulphate of baryta is left in solution. To 
the filtered solution diluted sulphuric acid is carefully added until all the baryta is 
precipitated as sulphate of baryta, when the solution of hyposulphuric acid is filtered 
off and evaporated in vacuo over oil of vitriol. It forms a colourless inodorous liquid, 
which is decomposed when heated, into hydrated sulphuric and sulphurous acids ; 
H 2 S 2 6 = H 2 O.S0 3 + S0 2 . Oxidising agents (nitric acid, chlorine, &c.) convert it 
into sulphuric acid. 

The hyposulphates are not of any practical importance ; they are all soluble, and 
are decomposed by heat, leaving sulphates, and evolving sulphurous acid. 

149. Trithionic acid (H 2 S 3 6 ), or sulphuretted hypositlphuric acid, is also a practi- 
cally unimportant acid, not known in the anhydrous state. Its hydrate is prepared 
from the trithionate of potash, which is formed by boiling a strong solution of bisul- 
phite of potash with sulphur until the solution becomes colourless, and filtering the 
hot solution from any undissolved sulphur — 

3(K 2 O.H 2 0.2S0 2 ) + S = 2(K 2 S 3 6 ) + K 2 O.S0 2 + 3H 2 . 
Bisulphite of potash. Trithionate of potash. 

The solution deposits trithionate of potash in prismatic crystals. By dissolving these 
In water, and decomposing the solution with perchloric acid, the potash is precipi- 
tated as perchlorate, and a solution of trithionic acid is produced, from which the 
hydrated acid has been obtained in crystals. It is, however, very unstable, being 
easily resolved into sulphurous acid, sulphuric acid, and free sulphur — 

H 2 S 3 6 = H 2 O.S0 3 + S0 2 + S. 

150. Tetrathionic acid, or bisulpliuretted hyposulphuric acid (H 2 S 4 6 ) is rather more 
stable than the preceding acid, though equally devoid of practical importance. It is 
formed when hyposulphite of baryta, suspended in a little water, is treated with 
iodine, when tetrathionate of baryta is obtained in crystals — 



2(BaS 2 3 ) + I 2 


= Bal 2 + BaS 4 6 . 


Hyposulphite 


Iodide of Tetrathionate 


of baryta. 


barium, of baryta. 



216 PREPARATION OF BISULPHIDE OF CARBON. 

By exactly precipitating the baryta from a solution of the tetrathionate by addi- 
tion of diluted sulphuric acid, the solution of tetrathionic acid may be obtained. 
When the solution is boiled, it is decomposed into sulphuric and sulphurous acids 
and free sulphur ; H 2 S 4 6 = H 2 O.S0 3 + S0 2 + S 2 . 

When solution of perchloride of iron is added to hyposulphite of soda, a fine purple 
colour is at first produced, which speedily vanishes, leaving a colourless solution. 
The purple colour appears to be due to the formation of the hyposulphite of sesqui- 
oxide of iron, which speedily decomposes, the ultimate result being expressed by the 
equation — 

Fe 2 Cl 6 + 2(Na 2 S 2 8 ) = Na 2 S 4 6 + 2FeCl 2 + 2NaCl. 

Perchloride Hyposulphite Tetrathionate Chloride of Chloride of 

of iron. of soda. of soda. iron. sodium. 

151. Pentathionic acid (H 2 S 5 6 ) possesses some interest as resulting from the action 
of sulphuretted hydrogen upon sulphurous acid, when much sulphur is deposited, 
and pentathionic acid remains in solution — 

5H 2 S + 5S0 2 = H 2 S s 6 + 4H 2 + S 5 . 

Pentathionic acid. 
To obtain a concentrated solution of the acid, sulphuretted hydrogen and sulphurous 
acid are passed alternately through the same portion of water until a large deposi- 
tion of sulphur has taken place. This is allowed some hours to settle; the clear 
liquid poured off and the solution concentrated by evaporation, first over a water- 
bath, and, finally, in vacuo, over oil of vitriol, for a concentrated solution of pentathi- 
onic acid is decomposed by heat into sulphuric and sulphurous acids, with separation 
of sulphur ; H 2 S 5 6 = H 2 O.S0 3 + S0 2 + S 3 . 

The true constitution of the preceding (yolytliionic) acids is not yet understood, 
but it may assist the memory to retain the usual mode of decomposition of the acids 
if they are represented as derived from oil of vitriol by successive additions of sulphu- 
rous acid and sulphur, thus — 

Oil of vitriol, . H 2 O.S0 3 = H 2 S0 4 

Hyposulphuric acid, H„0.S0 3 .S0 9 = H 2 S 2 6 

Trithionic ,, H 2 O.S0 3 .S0 2 .S = H 2 S 3 6 

Tetrathionic „ Hl0.S0 3 .S0 o .S 2 = HoS 4 6 

Pentathionic ,, H o O.S0 3 .S02.S 3 = H 2 S 5 6 

Bisulphide of Carbon. 
CS 2 = 76 parts by weight. 

152. This very important compound (also called bisulphuret of carbon) 
is found in small quantity among the products of destructive distillation 
of coal, and is very largely manufactured for use as a solvent for sulphur, 
phosphorus, caoutchouc, fatty matters, &c. It is one of the few com- 
pounds of carbon which can be obtained by the direct union of their 
elements, and is prepared by passing vapour of sulphur over charcoal 
heated to redness. 

In small quantity, bisulphide of carbon is easily prepared in a tube of German 
glass (combustion-tube) about two feet long and half-an-inch in diameter (fig. 213). 




Fig. 213 

This tube is closed at 
as to occupy 



closed at one end, and a few fragments of sulphur dropped into it, so 
two or three inches. The rest of the tube is filled up with small frag- 



PROPERTIES OF BISULPHIDE OF CARBON. 



217 




Fig. 214. 



merits of recently calcined wood charcoal. The tube is placed in a combustion- 
furnace, and its open end connected by a perforated cork with a glass tube, which 
dips just below the surface of water contained in a bottle placed in a vessel of very 
cold water. That part of the tube which contains the charcoal is first surrounded 
with red-hot charcoal, and when it is heated to redness, a little red-hot charcoal is 
placed near the end containing the sulphur (hitherto protected by a sheet-iron screen), 
so that the vapour of sulphur may be slowly passed over the red-hot charcoal. The 
bisulphide of carbon being insoluble in water, and much heavier (sp. gr. 1'27), is 
deposited beneath the water in the receiver. To purify the bisulphide of carbon 
from the water and the excess of sulphur which is deposited with it, the water is 
carefully drawn off with a small siphon, the bisulphide of carbon transferred to a 
Hash, and a few fragments of chloride of calcium dropped into it to absorb the water. 
A bent tube connected with a Liebig's con- 
denser, or with a worm, is attached to the 
flask (fig. 214) by a perforated cork, and the 
flask is gently heated in a water bath, when the 
bisulphide of carbon is distilled over as a perfectly 
colourless liquid. The inflammability of the 
bisulphide of carbon renders great care necessary. 

On a large scale, a fire-clay retort is 
filled with fragments of charcoal and 
heated to redness, pieces of sulphur being 
occasionally dropped in through an earthen- 
ware tube passing to the bottom of the 
retort, When very large quantities are 
made, coke is employed, and the vapour 
of sulphur is obtained from iron pyrites. 
The bisulphide of carbon is possessed of some very remarkable properties : 
it is a very brilliant liquid, the light passing through which is partly 
decomposed into its component coloured rays before it reaches the eye. 
These properties are dependent upon its high refractive and dispersive 
powers, which are turned to great advantage in optical experiments, espe- 
cially in spectrum analysis, where the rays emanating from a coloured 
flame are analysed by passing them through a prismatic bottle filled with 
bisulphide of carbon. It is also highly diathermanous, that is, it allows 
rays of heat to pass through it with comparatively little loss, so that if it 
be rendered opaque to light by dissolving iodine in it, the rays of light 
emanating from a luminous object may be arrested, whilst the calorific 
rays are allowed to pass. It has never been frozen, and is therefore em- 
ployed in thermometers for measuring very low temperatures. Bisulphide 
of carbon is a very volatile liquid, readily assuming the form of vapour 
at the ordinary temperature, and boiling at 118°*5 F. Its vapour, when 
diluted with air, has a very disgusting and exaggerated odour of sulphu- 
retted hydrogen, but the smell at the mouth of the bottle is ethereal and 
not unpleasant. 

The rapid evaporation of bisulphide of carbon is, of course, productive of great 
cold. If a few drops be placed in a watch-glass and blown upon, they soon pass off 
m vapour, and the temperature of the glass is so reduced that the moisture of the 
breath condenses upon it in hoar-frost, which melts when the glass is placed in the 
palm of the hand. If a glass plate be covered with water, a watch-glass containing 
bisulphide of carbon placed on it, and evaporation promoted by blowing through a 
tube, the watch-glass will be frozen on to the plate, so that the latter may be lifted 
up by it. 

The bisulphide of carbon is exceedingly inflammable ; it takes fire at 
a temperature far below that required to inflame ordinary combustible 
bodies, and burns with a bright blue flame, producing carbonic and sul- 



218 



PROPERTIES OF BISULPHIDE OF CARBON. 



phurous acids (CS 2 -f 6 = C0 2 + 2S0 2 ), and having a great tendency 
to deposit sulphur unless the supply of air is very good. 

If a little bisulphide of carbon be dropped into a small beaker, it may be inflamed 
by holding in its vapour a test-tube containing oil heated to about 300° F., which 
will be found incapable of firing gunpowder or of inflaming any ordinary com- 
bustible substance. 

The abundance of sulphur separated in the flame of bisulphide of carbon enables 
it to burn iron by converting it into sulphide. If some bisulphide of carbon be 
boiled in a test-tube provided with a piece of glass tube from which the vapour may 
be burnt, and a piece of thin iron wire be held in the flame (fig. 215), it will burn 
with vivid scintillation, the fusible sulphide of iron dropping off. 

The vapour of bisulphide of carbon acts very injuriously if breathed for 
any length of time, producing symptoms somewhat resembling those 
caused by sulphuretted hydrogen. Its poisonous properties have been 
turned to account for killing insects in grain without injuring it. 

The chief applications of bisulphide of carbon depend upon its power 

of dissolving the oils and fats. After as 
much oil as possible has been extracted 
from seeds and fruits by pressure, a fresh 
quantity is obtained by treating the 
pressed cake with bisulphide of carbon, 
which is afterwards recovered by distil- 
lation from the oil. In Algiers, bisulphide 
of carbon is employed for extracting the 
essential oils in which reside the perfumes 
of roses, jasmine, lavender, &c. 

Bisulphide of carbon has often been 
made a starting point in the attempts to 
produce organic compounds by synthesis. 
It may be employed in the formation of 
the hydrocarbons which are usually de- 
rived from organic sources, for if it be 
mixed with sulphuretted hydrogen (by 
passing that gas through a bottle contain- 
ing bisulphide of carbon gently warmed), and passed over copper-turn- 
ings heated to redness in a porcelain tube, olefiant gas will be pro- 
duced — 




Fig. 215. 



2CS 2 + 2H 2 S + Cu 6 



6CuS 



CA 



The action of bisulphide of carbon upon ammonia is practically im- 
portant for the easy production of sulphocyanide of ammonium, which is 
formed when the bisulphide of carbon is dissolved in alcohol, and acted 
on by ammonia with the aid of heat — 



CS 2 + 

Bisulphide of carbon. 



2NIL 



H 2 S 



+ NH 9 .HCNS . 

Sulphocyanide of ammoDium. 



Bisulphide of carbon is the sulphur-acid corresponding to carbonic acid, 
and is often called sulphocarbonic acid ; it combines with some of the 
sulphur-bases to form sulphocarbonates, which correspond to the car- 
bonates, containing sulphur in place of oxygen. Thus, when a solution 
of sulphide of potassium is mixed with au excess of bisulphide of carbon, 
the sulphocarbonate of (sulphide of) potassium is obtained in orange- 
yellow crystals. Even the hydrogen compound corresponding in compo- 
sition to the unknown hydrate of carbonic acid may be obtained as a 



CARBONIC OXYSULPHIDE. 219 

yellow oily liquid by decomposing sulphocarbonate of potassium with 
hydrochloric acid — 

K 2 S.CS 2 + 2HC1 = H 2 S.CS 2 + 2KC1 . 

Sulphocarbonate Hydrosulphocarbonic 

of potassium. acid. 

As would "be expected, the sulphocarbonates, when boiled with water, 
exchange their sulphur for oxygen, becoming carbonates — 

K 2 S.CS 2 + 3H 2 = K 2 O.C0 2 + 3H 2 S . 

The bisulphide of carbon vapour in coal-gas is one of the most injuri- 
ous of the impurities, and one of the most difficult to remove with economy. 
It is especially injurious, because when burning in the presence of aque- 
ous vapour, a part of its sulphur is converted into sulphuric acid, the cor- 
rosive effects of which are so damaging. Several processes have been 
devised for its removal. The gas has been washed with the ammoniacal 
liquor (containing hydrosulphate of ammonia) which absorbs the bisul- 
phide. Steam, at a high temperature, has been employed to convert it 
into hydrosulphuric and carbonic acids, which are both easily removed from 
the gas ; CS 2 + 2H 2 = C0 2 + 2H 2 S. Lime at a red heat decomposes it 
in a similar way; CS 2 + 3CaO = CaO.C0 2 + 2CaS. Oxide of lead 
dissolved in caustic soda has been used to convert it into sulphide of lead ; 
CS 2 + 2PbO + Na 2 = 2PbS + Na 2 O.C0 2 . Its removal as sulpho- 
carbonate by an alcoholic solution of potash or soda has also been pro- 
posed. At present, however, it retains its character as one of the most 
troublesome impurities with which the gas manufacturer has to deal. 

Carbonic oxysulphide, COS = 60 parts by weight = 2 volumes. This compound, 
which may be regarded as hydrosulphuric acid in which CO has replaced H 2 , is 
formed when a mixture of carbonic oxide with sulphur vapour is acted on by electric 
sparks, or passed through a red-hot porcelain tube. 

It is easily prepared by gently heating the sulphocyanide of potassium with oil of 
vitriol diluted with four-fifths of its volume of water, and collecting the gas over 
mercury. 

The action of the sulphuric acid upon the sulphocyanide produces hydrosulpho- 
cyanic acid ; KCNS (sulphocyanide of potassium) + H 2 S0 4 = HCNS + KHS0 4 ; 
which is then decomposed by the water, in the presence of the excess of sulphuric 
acid, into the carbonic oxy sulphide gas and ammonia, which combines with the sul- 
phuric acid ; HCNS + H 2 = NH 3 + COS. The gas has a peculiar disagreeable 
odour, recalling that of bisulphide of carbon ; it is more than twice as heavy as air 
(sp. gr. 2 -11), and is very inflammable, burning with a blue flame, and yielding carbonic 
and sulphurous acid gases. Potash absorbs and decomposes it, yielding carbonate of 
potash and sulphide of potassium ; COS + 4KHO = K 2 S + K 2 O.C0 2 + 2H 2 0. 

153. Bisulphide of silicon (SiS 2 ), corresponding in composition to bisulphide of 
carbon, is obtained by burning silicon in sulphur vapour, or by passing vajDour of bisul- 
phide of carbon over a mixture of silica and charcoal. Unlike the carbon compound, 
it is a white amorphous solid, absorbing moisture when exposed to air, and soluble in 
water, which gradually decomposes it into silicic and hydrosulphuric acids — 

SiS 2 + 2H 2 = Si0 2 + 2H 2 S . 

When heated in air, it burns slowly, yielding silicic and sulphurous acids. 

154. Sulphide of nitrogen (NS) is a yellow crystalline explosive substance, pro- 
duced by a complicated reaction which takes place when chloride of sulphur, dis- 
solved in bisulphide of carbon, is acted on by gaseous ammonia, when hydrochlorate 
of ammonia is deposited, and the filtered liquid, allowed to evaporate, deposits sul- 
phide of nitrogen mixed with sulphur, which may be dissolved out by bisulphide of 
carbon, in which the nitrogen compound is nearly insoluble ; this substance is re- 
markable for its sparing solubility, its irritating odour, and its explosibility when 
struck or moderately heated, its elements being held together by a very feeble at- 
traction. 



220 



SELENIUM. 



155. Chlorides op sulphur. — The subehloride, or chloride of sulphur 
(S a Cl 2 =135 parts by weight), is the most important of these, since it is 
employed in the process of vulcanising caoutchouc. It is very easily 
prepared by passing dry chlorine over sulphur very gently heated in a 
retort (fig. 216); the sulphur quickly melts, and the chloride of sulphur 




Fig. 216.— Preparation of chloride of sulphur. 

distils over into the receiver as a yellow volatile liquid (boiling point, 
280° F.), which has a most peculiar odour. It fumes strongly in air, the 
moisture decomposing it, forming hydrochloric and sulphurous acids, and 
causing a deposit of sulphur upon the neck of the bottle — 



2S 2 C1 2 



+ 2H 2 - 4HC1 + S0 2 + S 3 . 



When poured into water, it sinks (sp. gr. 1 -68) and slowly undergoes 
decomposition ; the separated sulphur, of course, belongs to the electro- 
positive variety (see p. 191), and the solution contains, beside hydrochloric 
and sulphurous acids, some of the acids containing a larger proportion of 
sulphur. If phosphorus dissolved in bisulphide of carbon be mixed with 
chloride of sulphur, the liquid will take fire on addition of ammonia. 
The specific gravity of the vapour of chloride of sulphur is 4*7, show- 
ing that it is 68 times as heavy as hydrogen, giving for its molecular 
weight 136, which agrees very nearly with that calculated (135). 

Bichloride of sulphur (SC1 2 ) is a far less stable compound than the chloride, from 
which it is obtained by the action of an excess of chlorine. It is a dark red fuming 
liquid, easily resolved, even by sunlight, into free chlorine and chloride of sulphur. 

Iodide of sulphur (SI 2 ) is a crystalline unstable substance, produced by the direct 
union of its elements, and occasionally employed in medicine. 

Subiodide of sulphur (S 2 I 2 ) is obtained in large tabular crystals resembling iodine, 
by decomposing the subchloride of sulphur with iodide of ethyle ; S 2 C1 2 + 2C 2 H 5 I = 
S 2 I 2 + 2C 2 H 5 C1 . 

Selenium. 

Se = 79 "5 parts by weight. 

156. Selenium (li\mn, the moon) is a rare element, very closely allied to sulphur 
in its natural history, physical characters, and chemical relations to other bodies. 
It is found sparingly in the free state associated with some varieties of native sul- 
phur, but more commonly in combination with metals, forming selenides, which are 
found together with the sulphides. The iron pyrites of Fahlun, in Sweden, is 
especially remarkable for the- presence of selenium, and was the source whence this 
element was first obtained. The Fahlun pyrites is employed for the manufacture of 



PROPERTIES OF SELENIUM. 221 

oil of vitriol, and in the leaden chambers a reddish brown deposit is found, which 
was analysed by Berzelius in 1817, and found to contain the new element. 

In order to extract selenium from the seleniferous deposit of the vitriol works, it 
may be boiled with sulphuric acid diluted with an equal volume of water, and nitric 
acid added in small portions until the oxidation is completed, when no more red 
fumes will escape. The solution, containing selenious (Se0 2 ) and selenic (Se0 3 ) 
acids, is largely diluted with water, filtered off from the undissolved matters, mixed 
with about one-fourth of its bulk of hydrochloric acid, and somewhat concentrated 
by evaporation, when the hydrochloric acid reduces the selenic to selenious acid — 

H 2 O.Se0 3 + 2HG1 = H 2 O.Se0 2 + H 2 + Cl 2 . 

A current of sulphurous acid gas is now passed through the solution, when the 
selenium is precipitated in fine red flakes, which collect into a dense black mass 
when the liquid is gently heated — 

H 2 O.Se0 2 + H 2 + 2S0 2 = 2(H 2 O.S0 3 ) + Se. 

The proportion of .selenium in the deposit from the leaden chambers is variable. The 
author has obtained above 3 per cent, by this process. 

Selenium, like sulphur, is capable of existing in three allotropic states : the red 
amorphous variety precipitated from its solutions, or sublimed like flowers of sul- 
phur; the black vitreous form; and the crystalline form deposited from. its solution 
in bisulphide of carbon, in which it is far less easily dissolved than sulphur. "When 
heated, it fuses easily, boils below a red heat, and is cunverted into a deep yellow 
vapour, which expands when heated in the same anomalous manner as vapour of 
sulphur. 

Selenium is less combustible than sulphur ; when heated in air it burns with a 
blue flame, and emits a peculiar odour like that of putrid horse-radish, which ap- 
pears to be due to the formation of a little selenietted hydrogen from the moisture 
of the air. When heated with oil of vitriol, selenium forms a green solution which 
deposits the selenium again when poured into water. 

Selenious acid (SeO a ), corresponding to sulphurous acid, is the product of combus- 
tion of selenium in oxygen. It is best obtained by dissolving selenium in boiling 
nitric acid (which would convert sulphur into sulphuric acid), and evaporating to 
dryness, when the selenious acid remains as a white solid which sublimes in needle- 
like crystals when heated. When dissolved in boiling water, it yields a crystalline 
hydrate of selenious acid. 

Selenic acid (Se0 3 ) is not known in the anhydrous state. It is formed when 
selenium is oxidised by fused nitre; K 2 O.N 2 5 + Se = K 2 Se0 3 + 2NO. By dis- 
solving the seleniate of potash in water, and adding nitrate of lead, a precipitate of 
seleniate of lead (PbO.Se0 3 ) is obtained, and if this be suspended in water and 
decomposed by passing hydrosulphuric acid gas, lead will be removed as insoluble 
sulphide, and a solution of hydrated selenic acid will be obtained — 

PbO.Se0 3 + H 2 S = H a O.Se0 3 j- PbS . 

This solution may be evaporated till it has a sp. gr. of 2 "6, when it very closely 
resembles oil of vitriol. It is decomposed, however, at about 550° F., evolving 
oxygen, and becoming selenious acid. It oxidises the metals like oil of vitriol, and 
even dissolves gold. The seleniates closely resemble the sulphates, but they are 
decomposed when heated Avith hydrochloric acid, chlorine being evolved, and selenious 
acid produced. 

Hydroselenic acid, or selenietted hydrogen (H 2 Se), is the exact parallel of sulphuretted 
hydrogen, and is produced by a similar process. It is even more offensive and 
poisonous than that gas, and acts in a similar way upon metallic solutions, precipi- 
tating the selenides. 

There are two chlorides of selenium: the dichloride, Se 2 Cl 2 a brown volatile liquid 
corresponding to dichloride of sulphur ; and the tetrachloride, SeCl 4 a white crystalline 
solid, without any well-established analogue in the sulphur series. 

Notwithstanding the resemblance between the two elements, there are two sul- 
phides of selenium, a bisulphide (SeS 2 ) and a tersulphide (SeS 3 ). The former is 
obtained as a yellow precipitate when hydrosulphuric acid is passed into solution of 
selenious acid. 

Tellurium. 
Te = 129 parts by weight. 
157. Tellurium (from tellies, the earth) is connected with selenium by analogies 



222 REVIEW OF THE SULPHUR GROUP. 

stronger than those which connect that element with sulphur. It is even less fre- 
quently met with than selenium, being found chiefly in certain Transylvanian gold 
ores. It occasionally occurs in an uncombined form, but more frequently in com- 
bination with metals. Foliated or graphic tellurium is a black mineral containing 
the tellurides of lead, silver, and gold. Telluride of bismuth is also found in nature. 

Tellurium is extracted from the foliated ore by a process similar to that for ob- 
taining selenium. From telluride of bismuth it is procured by strongly heating the 
ore with a mixture of carbonate of potash and charcoal, when telluride of potassium 
is formed, which dissolves in water to a purple-red solution, from which tellurium is 
deposited on exposure to air. 

Tellurium much more nearly resembles the metals than the non-metals in its 
physical properties, and is on that account often classed among the former, but it is 
not capable of forming a true basic oxide. In appearance it is very similar to bismuth 
(with which it is so frequently found), having a pinkish metallic lustre, and being, 
like that metal, crystalline and brittle. It fuses below a red heat, and is converted 
into a yellow vapour at a high temperature. When heated in air it burns with a blue 
flame edged with green, and emits fumes of tellurous acid (Te0 2 ) and a peculiar odour. 

Like selenium, tellurium is dissolved by strong sulphuric acid, yielding a purple- 
red solution, from which water precipitates it unchanged. 

The oxides of tellurium correspond in composition to those of selenium. Tellurous 
acid (Te0 2 ) is precipitated in the hydrated state when a solution of tellurium in 
diluted nitric acid is poured into water. If the nitric solution is boiled, a crystal- 
line precipitate of anhydrous tellurous acid is obtained. Unlike selenious acid, 
tellurous acid is sparingly soluble in water. It is easily fusible, forming a yellow 
glass, which becomes white on cooling, and it may be sublimed unchanged. Its acid 
character is rather feeble, and with some of the stronger acids, it forms soluble 
compounds in which it takes the part of a very feeble base. 

Telluric acid (Te0 3 ) is also a weak acid obtained by oxidising tellurium with nitre, 
precipitating the tellurate of potash with chloride of barium, and decomposing the 
tellurate of baryta with sulphuric acid. On evaporating the solution, crystals of 
hydrated telluric acid (H 3 O.Te0 3 .2H 2 0) are obtained, which become H 2 O.Te0 3 at 
a moderate heat, and when heated nearly to redness, are converted into an orange- 
yellow powder, which is the anhydrous acid. In this state it is insoluble in acids and 
alkalies. When strongly heated, it evolves oxygen, and becomes tellurous acid. 
The tellurates are unstable salts which are converted into tellurites when heated. 

Telluretted hydrogen, or hydrotelluric acid (H 2 Te), exhibits in the strongest manner 
the chemical analogy of tellurium with selenium and sulphur. It is a gas very 
similar to sulphuretted hydrogen in smell, and in most of its other properties. 
When its aqueous solution is exposed to the air, it yields a brown deposit of tellu- 
rium. When passed into metallic solutions it precipitates the tellurides. 

The gas is prepared by decomposing telluride of zinc with hydrochloric acid. 

The most characteristic property of tellurium compounds, is that of furnishing 
the purple solution of telluride ,of potassium, when fused with carbonate of potash 
and charcoal, and treated with water. Two solid chlorides of tellurium have been 
obtained ; TeCl 2 is a black solid with a violet coloured vapour, and is decomposed by 
water into tellurium and TeCl 4 . The latter may be obtained as a white crystalline 
volatile solid, decomposed by much water into hydrochloric and tellurous acids. 
There are also two sulphides of tellurium corresponding to the oxides, from which 
they may be obtained as dark brown precipitates, by the action of hydrosulphuric 
acid. They are both sulphur acids, and, therefore, soluble in alkaline sulphides. 

158. Review of the sulphur group of elements.. — The three elements — 
sulphur, selenium, and tellurium — exhibit a relation of a similar character 
to that observed between the members of the chlorine group, both in 
their physical and chemical properties. 

Sulphur is a pale yellow solid, easily fusible and volatile, without any 
trace of metallic lustre, and of specific gravity 2 '05 (sp. gr. of vapour, 
2-23). Selenium is either a red powder or a lustrous mass appearing 
black, but transmitting red light through thin layers ; much less fusible 
and volatile than sulphur, and of specific gravity 4 -8 (sp. gr. of vapour, 
5*68). Tellurium has a brilliant metallic lustre, is much less fusible and 
volatile than selenium, and of specific gravity 6-65 (sp. gr. of vapour, 9'0). 

Sulphur (atomic weight 32) has the most powerful attraction for oxy- 



EXTRACTION OF PHOSPHORUS FROM BONES. 223 

gen, hydrogen, and the metals. Selenium (atomic weight 79 -5) ranks 
next in the order of chemical energy. Tellurium (atomic weight 129) 
has a less powerful attraction for oxygen, hydrogen, and the metals, than 
either sulphur or selenium. This element appears to stand on neutral 
ground between the non-metallic bodies and the less electropositive 
metals. 

Sulphur, selenium, and tellurium are diatomic or bivalent elements. 



PHOSPHOEUS. 

P = 31 parts by weight.* 

159. This is the only element for the ordinary preparation of which 
animal substances are employed. It is never known to occur uncombined 
in nature, but is found abundantly in the form of phosphate of lime 
(3CaO.P 2 5 ), which is contained in the minerals coprolite, phosphorite, 
and apatite, and occurs diffused, though generally in small proportion, 
through all soils upon which plants will grow, for this substance is an 
essential constituent of the food of most plants, and especially of the 
cereal plants which form so large a proportion of the food of animals. 
The seeds of such plants are especially rich in the phosphates of lime and 
magnesia. 

Animals feeding upon these plants still further accumulate the phos- 
phoric acid, for it enters, chiefly in the form of phosphate of lime, into the 
composition of almost every solid and liquid in the animal body, and is 
especially abundant in the bones, which contain about three-fifths of 
their weight of phosphate of lime. It is from this source that our supply 
of phosphorus is chiefly derived. 



Composition of the Bones of Oxen. 

Animal matter, . 
Phosphate of lime, 
Fluoride of calcium, . 
Carbonate of lime, 
Phosphate of magnesia, 



30-58 

57-67 

2-69 

699 

2-07 



100-00 

What is here termed animal matter is a cartilaginous substance, con- 
verted into gelatine when the bones are heated with water under pressure, 
and containing carbon, hydrogen, nitrogen, and oxygen. It was formerly 
the custom to get rid of this by burning the bones in an open fire, but 
the increased demand for chemical products, and the diminished supply 
of bones, have taught economy, so that the cartilaginous matter is now 
dissolved out by heating the bones with water at a high pressure for the 
manufacture of glue; or the bones are subjected to destructive distilla- 
tion, so as to save the ammonia which they evolve, and the bone charcoal 
thus produced is used by the sugar-refiner until its decolorising powers 
are exhausted, when it is heated in contact with air to burn away the 
charcoal, and leave the hone-ash, consisting chiefly of phosphate of lime 
(3CaO.P 2 5 ). In order to extract the phosphorus, the bone-ash is heated 
for some time with diluted sulphuric acid, which removes the greater part 
of the lime in the form of the sparingly soluble sulphate of lime, leaving 

* The vapour of phosphorus is 62 times as heavy as hydrogen, so that its atom only 
occupies half a volume, if the atom of hydrogen be taken to occupy one volume. 



224 



PROPERTIES OF PHOSPHORUS. 



the phosphoric acid in the solution, which is strained from the deposit, 
evaporated to a syrup, mixed with charcoal, thoroughly dried in an iron 
pot, and distilled in an earthen retort (fig. 217), when the carbon removes 
the oxygen from the phosphoric acid, and the phosphorus distils over, 
and is condensed in a receiver containing water to protect it from the 
action of the air. The decomposition of the dried phosphoric acid by the 
carbon of the charcoal is expressed by the equation — 



H 2 O.P 2 5 + 

Hydrated phosphoric 
acid. 



a 



= 6CO + 

Carbonic oxide. 



H., + R 



This is the simplest account that can be given of the preparation of phosphorus 
from bone-ash, but it is not strictly correct, for the sulphuric acid does not remove 




Fig. 217.— Extraction of phosphorus. 



the whole of the lime from the phosphate, a portion remaining in the solution con- 
taining the phosphoric acid, so that this solution is generally said to contain swper- 
pliosp'hate of lime, and the action of the sulphuric acid is thus represented — 



Bone phosphate 
of lime. 



+ 2(H 2 O.S0 3 ) 



Ca0.2H 2 O.P 2 O s 

Superphosphate 
of lime. 



+ 2(CaO.S0 8 ). 



When the superphosphate of lime is dried, it becomes converted into mctaphos- 
2)hate of lime (CaO.P 2 5 ), and on distilling this with charcoal — 



3(CaO.P 2 5 ) 

Metaphosphate 

of lime. 



+ a 



= 3CaO.P 2 5 + 
Bone phosphate 
of lime. 



10CO + P a 



Silicic acid (sand) is sometimes added to combine with the lime, and liberate the 
remainder of the phosphoric acid, so that it may be decomposed by the charcoal. 

On the small scale, for the sake of illustration, phosphorus may be prepared by a 
process which has also been successfully employed for its manufacture in quantity, 
and consists in heating a mixture of bone-ash and charcoal in a stream of hydro- 
chloric acid gas — 



+ 6HC1 + a 



3CaCl, 



SCO + EL + P 9 



A mixture of equal weights of well-dried charcoal and bone-ash, both in fine 
powder, is introduced into a porcelain tube sheathed with copper, and placed in a 
charcoal furnace (fig. 218). One end of the tube is connected with a flask (A), con- 
taining fused salt and sulphuric acid for evolving hydrochloric acid, and the other is 
cemented with putty into a bent retort neck (B), for conveying the phosphorus 
into a vessel of water (C). On heating the porcelain tube to bright redness, phos- 
phorous distils over in abundance. The hydrogen and carbonic oxide inflame as 
they escape into the air, from their containing phosphorus vapour. 

When first prepared, the phosphorus is red and opaque, from the pre- 
sence of some suboxide of phosphorus and mechanical impurities ; the 
latter are removed by melting the phosphorus under warm water, and 



INFLAMMABILITY OF PHOSPHORUS. 



225 



squeezing it through wash leather. The phosphorus is then fused under 
ammonia to remove any acid impurity, and afterwards under bichromate 
of potash acidified with sulphuric acid, when the chromic acid oxidises 
the suboxide of phosphorus, and converts it into phosphoric acid which 
dissolves. The phosphorus is then thoroughly washed, melted under 
water, and drawn up into 
glass tubes, where it soli- 
difies into the sticks in 
which it is sold. These 
are always preserved un- 
der water from the action 
of oxygen, and in tin cases 
from that of light. 

Pure ordinary phospho- 
rus is almost colourless 
and transparent, but when 
exposed to light, and espe- 
cially to direct sun-light, 
it gradually acquires an 
opaque red colour, from 
its partial conversion into 
the allotropic variety 
known as red or amor- 
phous phosphorus. By 
tying bands of black cloth 
round a stick of phos- 
phorus and exposing it, 
under water, to the action 
of sun-light, alternate 
zones of red may be pro- 
duced. 

Even though the phosphorus be screened from light, it will not remain 
unchanged unless the water be kept quite free from air, which irregularly 
corrodes the surface of the phosphorus, rendering it white and opaque. 
This action is accelerated by exposure to light. - 

The most remarkable character of ordinary phosphorus is its easy in- 
flammability. It inevitably takes fire in air when heated a little above 
its melting point (111 -5 F.), burning with a brilliant white flame, which 
becomes insupportable when the combustion takes place in oxygen (p. 23), 
and evolving dense white clouds of solid phosphoric acid. When a piece 
of dry phosphorus is exposed to the air, it combines slowly with oxygen, 
forming phosphorous acid,* and its temperature often becomes so much 
elevated during this slow combustion, that it melts and takes fire, espe- 
cially if the combination be encouraged by the warmth of the hand or by 
friction. Hence, ordinary phosphorus must never be handled or cut in 
the dry state, but always under water, for it causes most painful burns. 

The slow oxidation of phosphorus is attended with that peculiar lumi- 
nous appearance which is termed phosphorescence (<£ws, light, <f>4p<D, tobear), 
but this glow is not seen in pure oxygen or in air containing a minute 
proportion of defiant gas or oil of turpentine. It will be remembered 

* The white fumes evolved by phosphorus in moist air are said to consist partly of 
nitrate of ammonia, formed by the action of the ozonised oxygen upon the air and aqueous 
vapour. 

P 




Fig. 218. 



226 



EXPERIMENTS WITH PHOSPHORUS. 




Fig. 219. 



that the slow oxidation of phosphorus is attended with the formation of 
ozone. 

The characteristic behaviour of phosphorus in air is best observed when the phos- 
phorus is in a finely-divided state. When a fragment of phosphorus is shaken with 
a little bisulphide of carbon, it is quickly dissolved, and if the solution be poured 
upon a piece of filtering-paper (fig. 219), and allowed to evaporate in a darkened 

room, the very thin film of phosphorus 
which is left will exhibit a glow increas- 
ing in brilliancy till the phosphorus bursts 
out into spontaneous combustion. 

If phosphorus be dissolved in olive oil, 
at a gentle heat, the solution is strongly 
phosphorescent when shaken in a bottle 
containing air, or when rubbed upon the 
hands. 

Characters may be written on paper 
with a stick of phosphorus held in a 
thickly -folded piece of damp paper (hav- 
ing a vessel of water at hand into which to plunge the phosphorus if it should 
take fire). When the paper is held with its back to the fire, or to a hot iron, 
in a darkened room, a twinkling combustion of the finely-divided phosphonis will 
ensue, and the letters will be burnt into the paper. Phosphorus, which has been 
partly oxidised, is even more easily inflamed than pure phosphorus. If a few small 
pieces of phosphorus be placed in a dry stoppered bottle, gently warmed till they 
melt, and then shaken round the sides of the bottle so as to become partly converted 
into red oxide of phosphorus, it will be found, long after the bottle is cold, to be 
spontaneously inflammable, so that if a wooden match tipped with sulphur be rubbed 
against it, the phosphorus which it takes up will ignite when the match is brought 
into the air, kindling the sulphur, which will inflame the wood. This was one of 
the earliest forms in which phosphorus was employed for the purpose of procuring 
an instantaneous light . If the stopper be greased, the phosphorus may be preserved 
unchanged for a long time. 

In the last experiment, if the wood had not been tipped with sulphur, the phos- 
phorus would not have kindled it, the flame of phosphorus generally being unable 
to ignite solid combustibles, because it deposits upon them a coating of phosphoric 
acid, which protects them from the action of air. Hence, in the manufacture of 
lucifer matches, the wood is first tipped with sulphur, or wax, or paraffine, which 
easily give off combustible vapours to be kindled by the flame of the phosphorus 
composition, and thus to inflame the wood. 

If a small stick of phosphorus be carefully dried with filtering paper, and dropped 
into a cylinder of oxygen, which is afterwards covered with a glass plate, no lumin- 
osity will be observed in a darkened room until the 
cylinder is placed under the air-pump receiver, and 
the air slowly exhausted. When the oxygen has thus 
been rarefied to about one-fifth of its former density, 
the phosphorescence will be seen. A similar effect 
may be produced by covering the cylinder of oxygen 
containing the phosphorus (having removed the glass 
plate) with another cylinder, about four times its size 
(fig. 220), filled with carbonic acid, which will 
gradually dilute the oxygen and produce phosphores- 
cence. By suspending — in a bottle of air containing 
a strongly luminous piece of phosphorus — a piece of 
paper with a drop of oil of turpentine upon it, the 
glow may be almost instantaneously destroyed. A 
small tube of olefiant gas or coal-gas dropped into 
the bottle will also extinguish the luminosity. 

Ordinary phosphorus is slowly converted into vapour at the ordinary 
temperature, and emits in the air white fumes with a peculiar alliaceous 
smell, which appear phosphorescent in the dark. When heated out of 
contact with air, it boils at 550° F., and is converted into a colourless 
vapour. 

The luminosity of phosphorus vapour is seen to advantage when a piece of phos- 




Fig. 220. 



PREPARATION OF AMORPHOUS PHOSPHORUS. 



227 



phorus is boiled with water in a narrow-necked flask, or a test-tube with a cork and 
narrow tube. The steam charged with vapour of phosphorus has all the appearance 
of a blue flame in a darkened room, but of course combustibles are not inflamed by- 
it, since its temperature is not higher than 212° F. Phosphorus may be distilledjwith 
perfect safety in an atmosphere of carbonic acid, the. neck of the retort being allowed 
to dip under water in the receiver. 

Although ordinary phosphorus is of a decidedly glassy or vitreous struc- 
ture, and not at all crystalline, it may be obtained in dodecahedral crys- 
tals, by allowing its solution in bisulphide of carbon to evaporate in an 
atmosphere of carbonic acid. 

The conversion of ordinary phosphorus into the red or amorphous phos- 
phorus is one of the most striking instances of allotropic modification. 
When phosphorus is heated for a considerable length of time to about 
450° F. in vacuo, or in an atmosphere in which it cannot burn, it becomes 
converted into a red infusible mass of amorphous phosphorus. This form 
of phosphorus differs as widely from the vitreous form as graphite differs 
from diamond. It is almost unchangeable in the air, evolves no vapour, 
is not luminous, cannot be inflamed by friction, or even by any heat short 
of 500° F., when it actually becomes reconverted into ordinary phos- 
phorus." Amorphous phosphorus is insoluble in the solvents for ordi- 
nary phosphorus. The two varieties also differ greatly in specific gravity, 
that of the ordinary phosphorus being 1-83, and of the amorphous 
variety 2'14. 

The conversion of vitreous into amorphous phosphorus may be effected by heating 
it in a flask (A, fig. 221) placed in an oil-bath (B), maintained at a temperature 
ranging from 450° to 460° F , the flask being furnished with a bent tube (C) dipping 
into mercury, and with another tube 
(D) for supplying carbonic acid gas, 
dried by passing over chloride of cal- 
cium. The flask should be thoroughly 
filled with carbonic acid before apply- 
ing heat, and the tube delivering it 
may then be closed with a small clamp 
(E). After exposure to heat for about 
forty hours, but little ordinary phos- 
phorus will remain, and this may be 
removed by allowing the mass to 
remain in contact with bisulphide of 
carbon for some hours, and subse- 
quently washing it with fresh bisul- 
phide of carbon till the latter leaves no 
phosphorus when evaporated. 

On the large scale, the red phos- 
phorus is prepared by heating about 
200 lbs. of vitreous phosphorus to 
450° F. in an iron boiler. After three or four weeks the phosphorus is found to be 
converted into a hard red brittle mass, which is ground by mill-stones under water, 
and separated from the ordinary phosphorus either by bisulphide of carbon or caustic 
soda, in which the latter is soluble. The temperature requires careful regulation, 
for if it be allowed to rise to 500°, the red phosphorus quickly resumes the vitreous 
condition, evolving the heat which it had absorbed during its conversion, and thus 
converting much of the phosphorus into vapour. This reconversion may be shown 
by heating a little red phosphorus in a narrow test-tube, when drops of vitreous 
phosphorus condense on the cool part of the tube. The colour of different specimens 
of amorphous phosphorus varies considerably ; that prepared on the large scale is 
usually of a dark purplish colour, but it may be obtained of a bright scarlet colour. 
Rhombohedral crystals of phosphorus, resembling crystals of arsenic in form and 

* According to Hittorf, the reconversion does not take place till 800° F., the red phos- 
phorus being convertible into vapour below that temperature, without fusion. 




Fig. 221. 



228 PRECIPITATION OF METALS BY PHOSPHORUS. 

metallic appearance, have been obtained by fusing phosphorus with lead, and dissolv- 
ing out the latter with diluted nitric acid (sp. gr. 1*1). 

Ordinary phosphorus is very poisonous, whilst amorphous phosphorus 
appears to be harmless. The former is employed, mixed with fatty sub- 
stances, for poisoning rats and beetles. Cases are, unhappily, not very 
rare, of children being poisoned by sucking the phosphorus composition 
on lucifer matches. The vapour of phosphorus also produces a very 
injurious effect upon the persons engaged in the manufacture of lucifer 
matches, resulting in the decay of the lower jaw-bone. This evil is much 
mitigated by good ventilation, or by diffusing turpentine vapour through 
the air of the work-room, and attempts have been made to obviate it 
entirely by substituting amorphous phosphorus for the ordinary variety, 
but, as might be expected, the matches thus made are not so sensitive to 
friction as those in which the vitreous phosphorus is used. 

The difference between the two varieties of phosphorus, in respect to 
chemical energy, is seen when they are placed in contact with a little 
iodine on a plate, when the ordinary phosphorus undergoes combustion, 
and the red phosphorus remains unaltered. 

Black phosphorus has been obtained by heating vitreous phosphorus to 
a little above its melting point and suddenly cooling it. It is reconverted 
by fusion and slow cooling. Viscous phosphorus results from the sudden 
cooling of phosphorus heated nearly to its boiling point. 

Ordinary phosphorus is capable of direct union with oxygen, chlorine, 
bromine, iodine, sulphur, and most of the metals, with which it forms 
'phosphides or phosphurets. Even gold and platinum unite with this 
element when heated, so that crucibles of these metals are liable to cor- 
rosion when heated in contact with a phosphate in the presence of a 
reducing agent, such as carbon. Thus the inside of a platinum dish or 
crucible is roughened when vegetable- or animal substances containing 
phosphates are incinerated in it. The presence even of small quantities 
of phosphorus in metallic iron or copper produces considerable effect upon 
their physical qualities. 

Phosphorus has the ]3roperty, a very remarkable one in a non-metal, of 
precipitating some metals from their solutions in the metallic state. If a 
stick of phosphorus be placed in a solution of sulphate of copper, it 
becomes coated with metallic copper, the phosphorus appropriating the 
oxygen. This has been turned to advantage in copying very delicate 
objects by the electrotype process, for by exposing them to the action of a 
solution of phosphorus in ether or bisulphide of carbon, and afterwards to 
that of a solution of copper, they acquire the requisite conducting metallic 
film, even on their finest filaments. Solutions of silver and gold are 
reduced in a similar manner by phosphorus. 

By floating very minute scales of ordinary phosphorus upon a dilute solution of 
chloride of gold, the metal will be reduced in the form of an extremely thin film, 
which may be raised upon a glass plate, and will be found to have various shades 
of green and violet by transmitted light, dependent upon- its thickness, whilst its 
thickest part exhibits the ordinary colour of the metal to reflected light. By heat- 
ing the films on the plate, various shades of amethyst and ruby are developed. If a 
very dilute solution of chloride of gold in distilled water be placed in a perfectly 
clean bottle, and a few drops of ether, in which phosphorus has been dissolved, 
poured into it, a beautiful ruby-coloured liquid is obtained, the colour of which is 
due to metallic gold in an extremely finely divided state, and on allowing it to stand 
for some months, the metal subsides as a purple powder, leaving the liquid colour- 
less. If any saline impurity be present in the gold solution, the colour of the reduced 
gold will be amethyst or blue. These experiments (Faraday) illustrate very strik- 



MANUFACTURE OF LUCIFER MATCHES. 229 

ingly the use of gold for imparting ruby and purple tints to glass and the glaze of 
porcelain. 

160. Lucifer matches are made by tipping the wood with sulphur or 
wax or paraffine to convey the flame, and afterwards with the match com- 
position, which is generally composed of saltpetre or chlorate of potash, 
phosphorus, red lead, and glue, and depends for its action on the easy 
inflammation, by friction, of phosphorus when mixed with oxidising agents 
like saltpetre (KN"0 3 ), chlorate of potash (KC10 3 ), or red lead (Pb 3 4 ), 
the glue only serving to bind the composition together and attach it to 
the wood. The composition used by different makers varies much in 
the nature and proportions of the ingredients. In this country, chlorate 
of potash is most commonly employed as the oxidising agent, such matches 
usually kindling with a slight detonation ; but the German manufacturers 
prefer either nitrate of potash or nitrate of lead, together with binoxide 
of lead or with red lead, which produce silent matches. 

Sulphide of antimony (which is inflamed by friction with chlorate of 
potash, see p. 163) is also used in those compositions in which a part of 
the phosphorus is employed in the amorphous form, and fine sand or 
powdered glass is very commonly added to increase the susceptibility 
of the mixture to inflammation by friction. 

The match composition is coloured either with ultramarine blue, Prus- 
sian blue, or vermilion. In preparing the composition, the glue and the 
nitre or chlorate of potash are dissolved in hot water, the phosphorus then 
added and carefully stirred in until intimately mixed, the whole being 
kept at a temperature of about 100° P. The fine sand and colouring 
matter are then added, and when the mixture is complete, it is spread out 
upon a stone slab heated by steam, and the sulphured ends of the matches 
are dipped into it. 

The safety matches, which refuse to ignite unless rubbed upon the 
bottom of the box, are tipped with a mixture of sulphide of antimony, 
chlorate of potash, and powdered glass, which is not sufficiently sensitive 
to be ignited by any ordinary friction, but inflames at once when rubbed 
upon the amorphous phosphorus mixed with glass which coats the rubber 
beneath the box. On this principle some French matches have been made 
which can be ignited only by breaking the match and rubbing the two 
ends together. 

It would be very desirable to dispense entirely with the use of phos- 
phorus in lucifer matches, not only because of the danger from accident 
and disease in the manufacture, but because a very large quantity of 
phosphate of lime which ought to be employed for agricultural purposes 
is now devoted to the preparation of phosphorus, of which six tons are 
said to be consumed annually in this country for the manufacture of 
matches. The most successful attempt in this direction appears to be the 
employment of a mixture of chlorate of potash and hyposulphite of lead, 
in place of the ordinary phosphorus composition. 

For illustration, very excellent matches may be made upon the small scale in the 
following manner. The slips of wood are dipped in melted sulphur so as^ to acquire 
a slight coating. 30 grains of gelatine or isinglass are dissolved in 2 drachms of 
water in a porcelain dish placed upon a steam-bath ; 20 grains of ordinary phosphorus 
are then added, and well mixed in with a piece of stick ; to this mixture are added, 
in succession, 15 grains of red lead and 50 grains of powdered chlorate of potash. 
The sulphured matches are dipped into this paste, and left to dry in the air. 

To make the safety matches : 10 grains of powdered chlorate of potash and 10 
grains of sulphide of antimony are made into a paste with a few drops of a warm 



230 



COMPOUNDS OF PHOSPHORUS AND OXYGEN. 



solution of 20 grains gelatine in 2 draclims water, the sulphured matches being tipped 
with this composition. The rubber is prepared with 20 grains of amorphous phos- 
phorus, and 10 grains of finely-powdered glass, mixed with the solution of gelatine, 
and painted on paper or card-board with a brush. 

161. Phosphorus-fuze composition. — To ignite the Armstrong percus- 
sion shells, a very sensitive detonating composition is employed, which is 
composed of amorphous phosphorus, chlorate of potash, shellac, and pow- 
dered glass made into a paste with spirit of wine. This is placed in the 
little cap designed for it, and when dry is waterproofed with a little 
shellac dissolved in spirit. 

Such a composition may be prepared with care in the following manner : — 4 grains 
of powdered chlorate of potash are moistened on a plate with 6 drops of spirit of wine, 
4 grains of powdered amorphous phosphorus are added, and the whole mixed at arm's 
length with a bone-knife, avoiding great pressure. The mixture, which should still 
be quite moist, is spread in small portions upon ten or twelve pieces of filtering paper, 
and left in a safe place to dry. If one of these be gently pressed with a stick, it 
explodes with great violence. It is dangerous to press it with the blade of a knife, 
as the latter is commonly broken, and the pieces projected with considerable force. 
A stick dipped in oil of vitriol of course explodes it immediately. If a bullet be 
placed very lightly upon one of the pellets, and the paper tenderly wrapped round it, 
a percussion shell may be extemporised, which explodes with a loud report when 
dropped upon the floor. 

Oxides of Phosphorus. 

162. There are only two compounds of phosphorus with oxygen which 
have been obtained and satisfactorily examined in the separate state, viz., 
phosphorous acid (P 2 3 ), and phosphoric acid (P 2 5 ). The sub-oxide of 
phosphorus (P 4 0) is said to have been obtained, but very little is known 
of it. 

Oxides of Phosphorus. 



Name. 


Formula. 


By Weight. 


Phosphorus. 


Oxygen. 


Suboxide of phosphorus ? ... 

Phosphorous acid 

Phosphoric acid 


P 4 

p 2 o 3 

i 3 2 o 5 


124 
62 

62 


16 

48 
80 



Phosphoric Acid. 
P 2 5 — 142 parts by weight. 

163. Phosphoric acid is by far the most important of the compounds 
of phosphorus. It has been already noticed as almost the only form of 
combination in which that element is met with in nature, and as an indis- 
pensable ingredient in the food of plants and animals. No other mineral 
substance can bear comparison with it as a measure of the capability of a 
country to support animal life. The acid itself is very useful in calico- 
printing and some other arts. 

The mineral sources of this acid appear to be phosphorite, coprolite, and 
apatite, all consisting essentially of phosphate of lime (3CaO.P 2 5 ), but 
associated in each case with fluoride of calcium, which is also contained, 
with phosphate of lime, in bones, and would appear to indicate an organic 
origin for these minerals. Phosphorite is an earthy-looking substance, 



PREPARATION OF PHOSPHORIC ACID. 



231 



forming large deposits in Estremadura. Apatite (from d7rarao>, to cheat, 
in allusion to mistakes in its early analysis) occurs in prismatic crystals, 
and is met with in the Cornish tin-veins. Both these minerals are largely 
imported from Spain, Norway, and America, for use in this country as a 
manure. 

Coprolites (Ko-rrpos, dung, \i$o<s, a stone, from the idea that they were 
petrified dung) are rounded nodules of phosphate of lime, which are 
found abundantly in this country. 

Large quantities of phosphoric acid, combined with lime and magnesia, 
are imported in the form of guano, the partially decomposed excrement of 
sea-fowl, which sometimes contains one-fourth of its weight of phosphoric 
acid. 

Bones, however, must be regarded as the chief immediate source whence 
the phosphate of lime for agricultural purposes is derived. 

Hydrated phosphoric acid is obtained from bone-ash by decomposing 
it with sulphuric acid, so as to remove as much of the lime as possible in 
the form of sulphate, which is strained off, and the acid liquid neutralised 
with carbonate of ammonia, which precipitates any unchanged phosphate 
of lime, and converts the phosphoric acid into phosphate of ammonia, 
consisting of phosphoric acid, water, and ammonia. On evaporating the 
solution, and heating the phosphate of ammonia, the ammonia is expelled, 
and hydrated phosphoric acid (H 2 O.P 2 5 ) is left in a fused state, solidify- 
ing to a glass on cooling. Thus prepared, however, it always retains some 



ammonia, and is contaminated with soda derived from the bones. 

The pure hydrated acid is prepared by oxidising phosphorus with 
diluted nitric acid (sp. gr. 1*2), and evaporating the solution in a platinum 
dish, until the hydrated phosphoric acid begins to volatilise in white 
fumes — 



5(H s O.NA) 



3(H,O.P,0 5 ) + 2H. 2 + lOM) 




Some phosphorous acid is formed at an intermediate stage. A transparent 
glass (glacial phosphoric acid) is thus obtained, which eagerly absorbs 
moisture from the air, and becomes liquid. 



232 



PHOSPHORIC ANHYDRIDE. 




The water cannot be separated from the hydrated phosphoric acid by 
the action of heat, so that the anhydrous phosphoric acid must be pre- 
pared by burning phosphorus in dry air. 

When required in considerable quantity, the anhydrous phosphoric acid {phos- 
phoric anhydride) is prepared by burning the phosphorus in a small porcelain dish 
(A. fig. 222) attached to a wide glass tube (B) for introducing the phosphorus, and 
suspended in a glass flask with two lateral necks, one of which is connected with a 
tube containing pumice-stone and oil of vitriol for drying the air as it enters, whilst 
the other neck is provided with a wide tube conveying the anhydrous phosphoric 
acid into a bottle connected, at C, with an aspirator, or cistern of water, for drawing 
air through the apparatus. The first piece of phosphorus is kindled by passing a 
hot wire down the wide tube, but afterwards the heat of the dish will always ignite 
the fresh piece as it is dropped in. The wide tube must be closed with a cork whilst 
the phosphorus is burning. 

A small quantity of anhydrous phos- 
phoric acid is more conveniently prepared 
by burning phosphorus under a large bell- 
jar of air, under which a shallow dish of 
oil of vitriol has been standing for an hour 
or two to dry the air. This dish is care- 
fully removed without disturbing the air 
within the jar, and the well-dried phos- 
phorus is introduced in a small porcelain 
crucible standing upon a large glass plate. 
The phosphorus having been kindled with 
a hot wire, the flakes of phosphoric acid 
will be seen falling like snow on to the glass 
plate^ where they accumulate in a layer of 
considerable thickness. To preserve it, 
the phosphoric acid must be immediately scraped up with a bone or platinum knife 
and thrown into a thoroughly dry stoppered bottle. 

Anhydrous phosphoric acid may be fused at a very high temperature, 
and even sublimed. Its great feature is its attraction for water; left 
exposed to the air for a very short time, it deliquesces entirely, becoming 
converted into hydrated phosphoric acid. It is often used by chemists as 
a dehydrating agent, and will even remove the water from oil of vitriol. 
When thrown into water, it hisses like a red-hot iron, but does not entirely 
dissolve at once, a few flakes of hydrated phosphoric acid remaining 
suspended in the liquid for some time. Phosphoric acid, like sulphuric 
acid, forms three definite combinations with water, but in the case of 
phosphoric acid, each of these three hydrates is a different acid, capable 
of producing different salts, whereas the sulphuric acid generates the same 
salts in whatever degree of hydration it is employed. 

The solution obtained by dissolving anhydrous phosphoric acid in 
water contains monohydrated phosphoric acid or metaphosphoric acid 
(H 2 O.P 2 5 ). If a little nitrate of silver be added to a portion of it, a 
transparent gelatinous precipitate is formed, which is the metaphosphate 
of silver (Ag,O.NA + H 2 O.P 2 5 = H 2 O.N 2 5 + Ag 2 O.P 2 5 ). 

If the solution of metaphosphoric acid be heated in a flask for a short 
time, it will lose the property of yielding a precipitate with nitrate of 
silver, unless one or two drops of ammonia be added to neutralise it, when 
an opaque white precipitate of pyrophosphate of silver (2Ag 2 O.P 2 5 ) is 
obtained, for the phosphoric acid has now been converted into the 
dihydrated or pyrophosphoric acid (2H 2 O.P 2 5 ). The formation of the 
precipitate is thus expressed — 

2H 2 O.P.A + 2(Ag 2 O.NA) + 2NH, = 2Ag 2 O.P 2 0, + 2(NH 3 .H 2 O.N 2 5 ). 



PYEOPHOSPHOEIC AND' OETHO-PHOSPHOEIC ACIDS. 233 

When the solution of pyrophosphoric acid is mixed with more water 
and boiled for a long time, it gives, when tested with nitrate of silver 
and a little ammonia, a yellow precipitate of triphosphate of silver 
(3Ag 2 O.P 2 5 ) ; the phosphoric acid having become converted into tri- 
hydrated phosphoric acid (3H 2 O.P 2 5 ), and acting upon the nitrate of 
silver in the presence of ammonia, thus — 

3H 2 O.P 2 5 + 3(Ag 2 O.N 2 5 ) + 3NH 3 = 3Ag 2 O.P 2 5 + 3(NH 3 .H 2 O.N 2 5 ). 

The pyrophosphoric acid (2H 2 O.P 2 5 ) cannot be obtained by the above 
process without an admixture of one of the other hydrates, but it has 
been obtained in crystals by decomposing the pyrophosphate of lead 
(2PbO.P 2 5 ) with hydro sulphuric acid, and evaporating the filtered solu- 
tion in vacuo over oil of vitriol. 

Trihydrated phosphoric acid may also be obtained in prismatic crystals, 
by evaporating its solution in a similar way. " This acid is also called 
ortho-phosphoric acid (6p66s, true), and common phosphoric acid, in allusion 
to the circumstance that the phosphates commonly met with and employed 
in the arts are the salts of this acid. 

For it will be perceived that each of these acids is able to combine 
with a quantity of base equivalent to the water present in the hydrate. 
Thus the metaphosphoric acid (H 2 O.P 2 5 ) forms salts with one molecule of 
a base having the general formula M 2 0, as in metaphosphate of soda, 
Na 2 O.P 2 5 . Pyrophosphoric acid (2H 2 O.P 2 5 ) forms salts with three 
molecules, as in triphosphate (or subphosphate) of soda, 3Na 2 O.P 2 5 . 

In the cases of pyrophosphoric and common phosphoric acids, it is not 
necessary that the two or three molecules of water should be displaced 
by the same base, for it is found that salts of these acids may be formed 
which contain two bases, and some in which part of the water does duty 
as a base. Examples of this kind are, the common phosphate of soda, 
2^Na 2 O.H 2 O.P 2 5 , which is derived from the acid, 
3H 2 O.P 2 5 , by the displacement of two molecules 
of water by soda; microcosmic salt, or phosphate 
of soda and ammonia, Na 2 0.(NH 4 ) 2 O.H 2 O.P 2 5 , 
where two molecules of the water in the acid are 
displaced respectively by soda and by the imaginary 
oxide of ammonium (NH 4 ) 2 0. A pyrophosphate of 
soda having the composition of Na 2 O.H 2 O.P 2 5 may 
be prepared, and is obviously derived from the acid, 
2H 2 O.P 2 5 , by the displacement of one molecule of 
water by soda. 

It is evident that when water or ammonia enters 
into the composition of the salt, the action of heat 
may cod vert an ortho-phosphate into a pyrophos- Fi S- 224 - 

phate, or even into a metaphosphate. 

Thus, if acrystal of the common rhombic phosphateof soda (2Na 2 O.H 2 O.P 2 5 .24Aq.) 
be heated gently in a crucible (fig. 224), it melts in its water of crystallisation, and 
gradually dries up to a white mass, the composition of which, if not heated beyond 
300° F. , will be 2jSTa 2 O.H 2 0. P 2 5 . If a little of this white mass be dissolved in water, 
the solution will be alkaline to red litmus paper ; and if nitrate of silver (itself 
neutral to test-papers) be added to it, a yellow precipitate of triphosphate of silver 
will be obtained, and the solution will become strongly acid — 

2Na 2 0. H 2 0. P 2 5 + 3( Ag 2 0. N 2 O s ) = 3 Ag 2 0. P 2 5 + 2(Na 2 0. F 2 5 ) + H 2 0. K 2 5 . 




234 PHOSPHOROUS ACID. 

If the dried phosphate of soda be now strongly heated over a lamp, it will lose its 
basic water, and become pyrophosphate of soda (w% fire). On dissolving this in 
water, the solution will be alkaline, and will give with nitrate of silver a white preci- 
pitate and a neutral solution — 

2Na 2 0. P 2 5 + 2( Ag 2 0. N 2 5 ) = 2 Ag 2 0. P 2 5 + 2(Na 2 0. N 2 5 ) . 

Microcosmic salt (Na 2 0.(NH 4 ) 2 O.H 2 O.P a 6 .8Aq.), when dissolved in water, yields 
an alkaline solution which gives a yellow precipitate with nitrate of silver, the liquid 
becoming acid — 
Na 2 0(NH 4 ) 2 O.H 2 O.P 2 5 +3(Ag 2 O.N 2 5 )=3Ag 2 O.P 2 5 + Na 2 O.N 2 5 + (NH,) 2 O.N 2 5 + H 2 O.N 2 5 

But if the salt be heated in a crucible, it fuses, evolving water and ammonia, and 
leaving a transparent glass of metaphosphate of soda (Na 2 0.P 2 6 ), which may be dis- 
solved by soaking in water, yielding a slightly acid solution, which gives a white 
gelatinous precipitate with nitrate of silver, the liquid being neutral— 

Na 2 O.P 2 5 + Ag 2 0. N 2 5 = Ag 2 0. P 2 5 + Na 2 0. N 2 5 . 

The crystallised metaphosphate of soda retains 1 molecule of water when dried at 
212° F. , becoming Na 2 0. P 2 6 . H 2 0. On heating this to 300° F. , the salt is converted 
into the acid pyrophosphate of soda, Na. 2 O.H 2 0.P 2 5 , the water having assumed a 
basic character in the salt. 

All the phosphates may be converted into tribasic phosphates, by fusing them 
with an alkaline hydrate or carbonate.* 

164. Phosphorous acid (P 2 3 ) is the product of the slow combustion of phosphorus. 
If a piece of phosphorus be heated in a long glass tube, into which a very slow cur- 
rent of dry air is drawn through a very narrow tube, it burns with a pale blue flame, 
and white flakes of anhydrous phosphorous acid are deposited. Phosphorous acid is 
more easily converted into vapour than phosphoric acid. It eagerly absorbs mois- 
ture from the air, and is decomposed when strongly heated in a sealed tube, yielding 
free phosphorus and phosphoric acid ; 5P 2 3 = 3P 2 5 + P 4 . 

Hydrated phosphorous acid is obtained in solution, mixed with phosphoric acid, 
when sticks of phosphorus arranged in separate tubes, open at both ends, and placed 
in a funnel over a bottle, are exposed under a bell-jar, open at the top, to air satu- 
rated with aqueous vapour. To obtain the ptire acid, chlorine is very slowly passed 
through phosphorus fused under water, when the terchloride of phosphorus first 
formed is decomposed by the water into phosphorous and hydrochloric acids ; 
2PCl 3 + 6H 2 = 3H 2 O.P 2 3 + 6HCl. The hydrochloric acid is expelled by a mode- 
rate heat, when the Irydrated phosphorous acid is deposited in prismatic crystals. 
The water cannot be separated from phosphorous acid by heat ; when the hydrate 
is heated, it is decomposed into hydrated phosphoric acid and gaseous phosphuretted 
hydrogen ; 4(3H 2 0. P 2 3 ) = 3(3H 2 0. P 2 5 ) + 2PH 3 . 

Solution of phosphorous acid gradually absorbs oxygen from the air, becoming 
phosphoric acid. This tendency to absorb oxygen causes it to act as a reducing 
agent upon many solutions ; thus it precipitates finely -divided metallic silver from 
a solution of the nitrate, by which its presence may be recognised in the water in 
which ordinary phosphorus has been kept. The solution of phosphorous acid even 
reduces sulphurous acid, producing sulphuretted hydrogen and sulphur, the latter 
being formed by the action of the sulphuretted hydrogen upon the sulphurous acid ; 
2S0 2 + 2H 2 + 3(3H 2 0. P 2 3 ) = 2H 2 S + 3(3H 2 0. P 2 5 ) . 

If solution of phosphorous acid be poured into a hydrogen apparatus, some phosphu- 
retted hydrogen is formed which imparts a fine green tint to the hydrogen flame. 
When solution of phosphorous acid is mixed with a slight excess of solution of soda, 
and carefully evaporated, crystals are deposited which have the composition 
2Na 2 0.P 2 3 .llH 2 . From these crystals, however, only 10 molecules of water can 
be separated, even at 570° F., leading to the belief that the elements of the last 
molecule of water really belong to the acid itself, and that the true formula of the 
phosphite of soda dried at that temperature is 2Na 2 0.H 2 0.P 2 3 , or Na 2 PH0 3 . If 
this view be correct, phosphorous acid should form two classes of salts ; accordingly, 
we find the acid phosphites containing only one molecule of base, the absent mole- 
cule being represented by water. Thus, acid phosphite of baryta dried at 212° F. 
has the composition Ba0.2H 2 0.P„0 3 , or BaP 2 H 4 6 . When heated, the phosphites 
are converted into phosphates at the expense of the oxygen of the water contained 

* It has been remarked that the pliancy of the acid character of phosphoric acid parti- 
cularly fits it to take part in the vital phenomena. It may be regarded as three acids 
in one. 



SUBOXIDE OF PHOSPHORUS. 235 

in them, the hydrogen being evolved, often accompanied by phosphuretted 
hydrogen. 

165. Hypophosphorous acid. — When phosphorus is boiled with hydrate of baryta 
and water, the latter is decomposed, its hydrogen combining with part of the phos- 
phorus to form phosphuretted hydrogen (spontaneously inflammable), which escapes, 
whilst the oxygen of the water unites with another part of the phosphorus, forming 
hypophosphorous acid, which combines with baryta and water to form hypophosphite 
of baryta ; this may be obtained by evaporating the solution, in crystals having the 
composition BaP 2 H 4 4 . The action of phosphorus upon hydrate of baryta may 
be represented by the equation — 

3(BaO.H 2 0) + 6H 2 + P 8 = 3(BaP 2 H 4 4 ) + 2PH 3 . 
Hydrate of Hypophosphite Phosphuretted 

baryta. of baryta. hydrogen. 

Some phosphate of baryta (3BaO.P 2 5 ) is also formed at the same time, as the result 
of a secondary action. 

By dissolving the hypophosphite of baryta in water, and decomposing it with the 
requisite quantity of sulphuric acid, so as to precipitate the baryta as sulphate, a 
solution is obtained which may be concentrated by careful evaporation till it has 
the composition represented by the formula H 2 P 2 H 4 4 . If this hydrated hypophos- 
phorous acid be heated, it evolves phosphuretted hydrogen, and becomes converted 
into hydrated phosphoric acid ; 2(H 2 P 2 H 4 4 ) = 3H 2 0. P 2 5 + 2PH 3 . When exposed 
to the air it absorbs oxygen, and becomes converted into phosphorous and phosphoric 
acids. It is a more powerful reducing agent than phosphorous acid. The latter 
acid does not reduce a solution of sulphate of copper, but hypophosphorous acid when 
gently warmed with it, gives a black precipitate of hydride of copper (CuH), which 
is decomposed by boiling, evolving hydrogen and leaving metallic copper. 

When heated, the hypophosphites evolve phosphuretted hydrogen, and are con- 
verted into phosphates. The hypophosphite of soda (]STa 2 P 2 H 4 4 ) is sometimes used 
in medicine ; its solution has been known to explode with great violence during 
evaporation, probably from a sudden disengagement of phosphuretted hydrogen. 

The phosphorous and hypophosphorous acids may be connected with phosphoric 
acid in the following manner — 

Anhydrous phosphoric acid P2O5 

Metaphosphoric ,, H 2 O.P 2 5 = H 2 O.P 2 3 2 " 

Hypophosphorous ,, H 2 O.P 2 3 H 4 ' 

Pyrophosphoric „ 2H 2 O.P 2 5 = 2H 2 O.P 2 4 

Phosphorous „ 2H 2 O.P 2 4 H 2 

where hypophosphorous acid is derived from metaphosphoric acid by displacing 
two atoms of diatomic oxygen by four atoms of monatomic hydrogen ; and phospho- 
rous acid is derived from pyrophosphoric acid by displacing one atom of diatomic 
oxygen by two atoms of monatomic oxygen. 

166. Suboxide of phosphorus is supposed to constitute the yellow or red residue 
which is left in the dish when phosphorus 
burns in air, but it is always mixed with much 
phosphoric acid. If phosphorus be melted 
under water in a flask (fig. 225), and oxygen 
gis be allowed to bubble through it (a brass 
tube being employed to convey the oxygen), 
each bubble of the gas produces a brilliant 
flash, and the phosphorus is converted into 
red flakes, which were believed to be suboxide 
of phosphorus, but are really amorphous phos- 
phorus. The true suboxide of phosphorus (P 4 0) 
appears to be formed when small pieces of 
phosphorus are covered with terchloride of -pi*. 225. 
phosphorus, exposed to the air, and afterwards 

heated with water, when the suboxide is deposited as a yellow powder, becoming 
red at high temperatures, and inflaming when heated in air. 




236 



GASEOUS PHOSPHURETTED HYDROGEN. 



Phosphides of Hydrogen. 

167. Although phosphorus and hydrogen do not combine directly, 
there are three compounds of these elements producible by processes of 
substitution, the composition of which is shown in the following table : — 



Name. 


Formula. 


By Weight. 


Phosphorus. 


Hydrogen. 


Phosptmretted hydrogen gas 
Liquid phosphide of hydrogen . 
Solid phosphide 


PH 3 j 

PH 2 

P 2 H? 


31 
31 

62 


3 

2 
1 



/r;X^"i^-: 



Phosphuretted hydrogen gas (PH 3 = 34 parts by weight = 2 vols. = 
vol. P + 3 vols. H) is by far the most important of these. It has 

been mentioned above as result- 
ing from the action of heat upon hy» 
drated phosphorous acid, and when 
prepared by this process it is ob- 

rtained as a colourless gas, with a 
most powerful odour of putrid fish, 
inflaming on the approach of a light, 
and burning with a brilliant white 
flame, producing thick clouds of 
phosphoric acid. It is slightly 
heavier than air (sp. gr. 1*19), and 
has been liquefied under high pres- 
sure. 




Fig. 226.— Preparation of phosphuretted 
hydrogen. 



The ordinary method of preparing this 
gas for experimental purposes consists in 
boiling phosphorus with a strong solution 
of potash, when water is decomposed, its 
hydrogen combining with one part of the 
phosphorus, and its oxygen with another part forming hypophosphorous acid, which 
unites with the potash. 

A few fragments of phosphorus are introduced into a small retort (fig. 226), 
which is then nearly filled with a strong solution of potash (sp. gr. 1'3*), and 
heated. The extremity of the neck of the retort should not be plunged under 
water until the spontaneously inflammable gas is seen burning at the orifice, 
and the retort must not be placed close to the face of the operator, since explo- 
sions sometimes take place in preparing the gas, and the boiling potash produces 
dangerous effects. The gas may be collected in small jars filled with water, 
taking care that no bubble of air is left in them. It contains phosphuretted 
hydrogen, mixed with free hydrogen, the latter being formed from the deoxidation 
of water by the hypophosphite of potash. As each bubble of this gas escapes into 
the air through the water of the pneumatic trough, it burns with a vivid white 
flame, producing beautiful wreaths of smoke (phosphoric acid), resembling the 
gunner's rings sometimes seen in firing cannon. Small bubbles sometimes escape 
without spontaneously inflaming. If a bubble be sent up into a jar of oxygen, 
the flash of light is extremely vivid, and the jar must be a strong one to resist 
the concussion. It is advisable to add a trace of chlorine to the oxygen to 
insure the inflammation of each bubble, for an accumulation of the gas would shatter 
the jar. 

If this gas be passed through a tube cooled in a freezing mixture of ice and salt, 
the gas escaping from the tube is found to have lost its spontaneous inflammability, 

* 450 grains of common stick potash dissolved in 1000 grains of water. 



CHLOEIDES OF PHOSPHORUS. 237 

although, it takes fire on contact with flame. The cold tube contains the liquid 
phosphide of hydrogen (PH 2 ), which was present in the gas in the state of vapour, and 
caused its spontaneous inflammability, for as soon as this liquid comes in contact 
with air it takes fire. When exposed to light, the liquid phosphide is decomposed 
into phosphuretted hydrogen gas and a yellow solid phosphide (P 2 H), which is not 
spontaneously inflammable; 5PH 2 = P 2 H + 3PH 3 . It is for this reason that the 
spontaneously inflammable gas loses that property when kept (unless in the dark), 
depositing the solid phosphide upon the sides of the jar. 

By passing a few drops of oil of turpentine up through the water into a jar of the 
spontaneously inflammable gas, this property will be entirely destroyed, whereas 
the addition of a trace of nitrous acid imparts spontaneous inflammability. 

Phosphuretted hydrogen, when passed through solutions of some of the metals, 
precipitates their phosphides. For example, with sulphate of copper it gives a 
black precipitate of phosphide of copper — 

3(CuO.S0 3 ) + 2PH 3 = 3(H 2 O.S0 8 ) + P 2 Cu 3 . 
When this black precipitate is heated with solution of cyanide of potassium, it 
evolves self lighting phosphuretted hydrogen.* In fact this is one of the easiest 
and safest methods of preparing this gas ; for the phosphide of copper is readily ob- 
tained by simply boiling phosphorus in a solution of sulphate of copper. 

Phosphuretted hydrogen has great pretensions to rank as the chemical analogue 
of ammonia, for although it has no alkaline properties, it is capable of combining 
with hydrobromic and hydriodic acids to form crystalline compounds analogous to 
the hydrobromate and hydriodate of ammonia ; these compounds, however, are de- 
composed by water. It will be seen hereafter, that when the hydrogen of phos- 
phuretted hydrogen is displaced by certain compound radicals, such as ethyle, power- 
ful organic bases are produced. 

The spontaneously inflammable phosphuretted hydrogen may also be obtained 
by throwing fragments of phosphide of calcium into water ; this substance is pre- 
pared by passing vapour of phosphorus over red-hot quick-lime, or simply by heat- 
ing small lumps of quick-lime to bright redness in a crucible and throwing in frag- 
ments of phosphorus, closing the crucible immediately. The dark brown mass thus 
obtained is a mixture of pyrophosphate of lime and phosphide of calcium, of some- 
what variable composition. 

When phosphuretted hydrogen gas is decomposed by a succession of electric sparks, 
2 vols, of the gas yield 3 vols, of hydrogen, the phosphorus being deposited in the 
red or amorphous form. 

168. Two chlorides of phosphorus are known. The terchloride (PC1 3 ) is prepared 
by acting upon phosphorus with perfectly dry chlorine in the apparatus employed (p. 
220) for preparing the chloride of sulphur. Terchloride of phosphorus distils over 
very easily (boiling-point, 173 0, 4 F.), as a colourless pungent liquid (sp. gr. 1'62), 
which fumes strongly in air, its vapour decomposing the moisture of the air and pro- 
ducing hydrochloric acid fumes. In contact with water the liquid is immediately 
decomposed, yielding hydrochloric and phosphorous acids, as described for the pre- 
paration of the latter acid (p. 234). Its analogy to anhydrous phosphorous acid is 
shown by its absorbing oxygen when boiled in the presence of that gas, and forming 
the oxy chloride of phosphorus (PC1 3 0) corresponding in composition to anhydrous 
phosphoric acid. It also absorbs chlorine with avidity, becoming converted into 
pentachloride of phosphorus (PC1 5 ). This compound, however, is more conveniently 
prepared by passing chlorine through a solution of phosphorus in bisulphide of carbon, ' 
carefully cooled. On evaporation, the pentachloride of phosphorus is deposited in 
white prismatic crystals, which volatilise below 212° F., and fume when exposed to 
air, from the production of hydrochloric acid. When thrown into water it is decom- 
posed into phosphoric and hydrochloric acids ; 2PC1 5 + 8H 2 = 3H 2 O.P. 2 5 + 
10HC1. But if it be allowed to deliquesce in air, only a partial decomposition 
takes place, and the oxychloride of phosphorus is formed ; 

PC1 S + H 2 = PC1 3 + 2HC1. 
This oxychloride of phosphorus may also be produced by heating pentachloride 
of phosphorus with anhydrous phosphoric acid ; P 2 5 + 3PC1 S = 5PC1 3 . A 
more instructive method of preparing it consists in distilling the pentachloride of 
phosphorus with crystallised boracic acid — 

3PC1 5 + 3H 2 O.B 2 3 = 3PC1 3 + 6HC1 + B 2 3 . 

* Cyanide of copper and phosphide of potassium being formed, and the latter decom- 
posed by water, giving phosphuretted hydrogen, and hypophosphite of potash. 



26$ ACTION OF IODINE ON PHOSPHORUS. 

Some of the hydrated organic acids (succinic, for example) may be obtained in 
the anhydrous state, as the boracic acid is in this case, by distillation with penta- 
chloride of phosphorus. The oxychloride of phosphorus distils over (boiling point, 
230° F. ) as a heavy (sp. gr. 1*7) colourless fuming liquid of pungent odour. Of 
course it is decomposed by water, yielding hydrochloric and phosphoric acids. It 
will be found of the greatest use in effecting certain transformations in organic sub- 
stances. 

The analogy between water and hydrosulphuric acid would lead to the expecta- 
tion that a sulphochloride of phosphorus (PC1 3 S), corresponding to the oxychloride, 
would be formed by the action of hydrosulphuric acid upon pentachloride of phos- 
phorus ; PC1 5 + H 2 S = PC1 3 S + 2HC1. It is a colourless fuming liquid, which is 
slowly decomposed by water, giving phosphoric, hydrochloric, and hydrosulphuric 
acids ; 2PC1 3 S + 8H 2 = 3H 2 O.P 2 5 + 6HC1 + 2H 2 S. When acted on by solu- 
tion of soda, the sulphochloride of phosphorus loses its chlorine to the sodium, 
and acquires an equivalent quantity of oxygen, a sulphoxy -phosphate of soda 
(3Na 2 O.P 2 3 S 2 .24H 2 0) being deposited in crystals. This salt evidently corresponds 
in composition to the triphosphate of soda (3Na 2 O.P 2 5 .24H 2 0), and its production 
is expressed by the equation; 2PC1 3 S + 6Na 2 = 6NaCl + 3Na 2 O.P 2 3 S 2 . Salts 
of similar composition may be obtained with other metallic oxides. 

The bromides and oxybromide of phosphorus correspond to the chlorine com- 
pounds. 

Iodine in the solid state combines very energetically with phosphorus, but if the 
two elements be brought together in a state of solution in bisulphide of carbon, a 
more moderate action ensues, and two iodides of phosphorus may be obtained in crys- 
tals; a teriodide (PI 3 ) corresponding to the terchloride, and a biniodide (PI 2 ), 
which has no analogue either among the oxygen, chlorine, or bromine compounds 
of phosphorus. 

The addition of a very small quantity of iodine to ordinary phosphorus, fused in a 
flask filled with carbonic acid gas, materially accelerates its conversion into the red 
modification, and allows the change to be effected at a much lower temperature 
than that required when the phosphorus is heated alone. This has been ascribed 
to the disposition of the electro-negative iodine to cause the phosphorus to assume 
the positive or amorphous state when entering into combination with it ; this com- 
pound being decomposed by heat with separation of amorphous phosphorus, the 
iodine combines with a fresh portion of the phosphorous, which is converted in the 
same way. 

169. The sulphides of phosphorus may be formed by the direct combination of their 
elements. If ordinary phosphorus be used, the experiment is not unattended with 
danger, and should be performed under water. It is safer to combine the amor- 
phous phosphorus with sulphur, at a moderate heat, in an atmosphere of carbonic 
acid. 

There appear to be at least three sulphides of phosphorus, viz., the protosulphide 
(P 2 S), the sesquisulphide (P 2 S 3 ), representing phosphorous acid (P 2 3 ), and thepenta- 
sulphide (P 2 S 5 ), analogous to phosphoric acid (P 2 5 ) . 

P 2 S is a yellow oily liquid which may be distilled out of contact with air. 

P 2 S 3 is a yellow solid, easily fusible, and capable of subliming in a crystalline 
form if air be excluded. It may be produced by the action of hydrosulphuric acid 
upon terchloride of phosphorus ; 2PC1 3 + 3H 2 S = P 2 S 3 + 6HC1. 

P 2 S 5 crystallises more readily in a fused state than P 2 S 3 . Both these sulphides, 
unlike the protosulphide, are easily decomposed by water. All the sulphides are 
sulphur-acids. 

170. Action of ammonia upon anhydrous phosphoric acid. — Some remarkably stable 
and definite compounds, containing nitrogen and phosphorus, are derived from the 
action of ammonia on anhydrous phosphoric acid, and the study of their mode of 
formation will be found to throw some light upon the history of a very large and 
important class of organic substances known as the amides. 

Anhydrous phosphoric acid absorbs ammoniacal gas with great evolution of heat, 
and produces, not phosphate of ammonia, for that cannot be formed unless water is 
present, but the ammoniacal salt of a new acid, phosphamic acid, which contains the 
elements of acid phosphate of ammonia (NH 4 ) 2 0.2H 2 O.P 2 5 ) minus four molecules 
of water — 

2NH 3 + P 2 5 = H 2 + 1T 2 H 4 2 4 (Phosphamic acid) . 



ARSENIC. 239 

When gently heated with water, phosphamic acid is converted into acid phosphate 
of ammonia. 

When the phosphamate of ammonia is heated in a current of dry ammonia, it 
gives off water, and leaves a yellow insoluble substance formerly supposed to be 
phosphide of nitrogen, but now known as phospham— 

2NH 3 .H 2 O.N 2 H 4 P 2 4 [Phosphamate of ammonia) = 5H 2 + 2N 2 HP (Phospham). 

It is not surprising that the presence of hydrogen in this substance should have 
been overlooked, for it may be heated to redness (out of contact with air) without 
alteration, is unaffected by chlorine, and is very slowly acted upon by nitric acid. 

Action of ammonia on oxychloride of phosphorus. 
PClgO (Oxychloride of phosphorus) + 3NH g = 3HC1 + jST 3 H 6 PO (Phosphotriamide) . 

Of course the hydrochloric acid combines with the excess of ammonia to form 
hydrochlorate of ammonia, which may be washed out with water, leaving the phos- 
photriamide as a white insoluble solid, not easily attacked by acids or alkalies. It 
may be regarded as triphosphate of ammonia (3(NH 4 ) 2 0. P 2 5 ) minus six molecules of 
water, which would furnish two molecules of phosphotriamide. 

If sulpbochloride of phosphorus be submitted to the action of ammonia, sulphos- 
photriamide is obtained — 

PC1 3 S + 3NH 3 = 3HC1 + N 3 H 6 PS. 

S V^^° l Sulphosphotriamide. 

This compound may evidently be regarded as sulphophosphate of (sulphide of) 
ammonium (3(NH 4 ) 2 S.P 2 S 5 ) minus six molecules of hydrosulphuric acid. 

Action of ammonia on pentacliloride of phosphorus. 

PC1 5 + 2NH 3 = 2HC1 + N 2 H 4 PC1 3 (Ch!orophosphamide) . 

The hydrochloric acid combines with the excess of ammonia, forming hydrochlorate 
of ammonia. By boiling chlorophosphamide with water, a very stable insoluble sub- 
stance is obtained, known as phosphodiamide — 

N 2 H 4 PC1 3 (Chlorophosphamide) + H 2 = N 3 H 3 PO (Phosphodiamide) + 3HC1 . 

This substance may be represented as derived from the phosphate of ammonia 
(2(NH 4 ) 2 O.H 2 O.P 2 d 5 ) by the abstraction of six molecules of water, furnishing two 
molecules of phosphodiamide. 

When phosphodiamide is heated it loses ammonia and becomes monophosphamide — 

N.HgPO = NH 3 + NPO. 

Phosphodiamide. Monophosphamide. 

which may be regarded as acid phosphate of ammonia ((NH 4 ) 2 0.2H 2 O.P 2 5 ) minus 
six molecules of water, yielding two molecules of monophosphamide. 

The phrase amides of phosphoric acid refers to those substances which may be 
represented as derived from the phosphates of ammonia by the loss of a certain 
number of molecules of water ; thus — 

(NH 4 ) 2 0.2H 2 O.P 2 5 — 6H 2 = 2NPO Monophosphamide. 

2(KH 4 ) 2 O.H 2 O.P 2 5 — 6H 2 = 2N" 2 H 3 PO Phosphodiamide. 
3(NH 4 ) 2 O.P 2 5 — 6H 2 = 2N 3 H 6 PO Phosphotriamide. 

AH these substances yield ammonia and phosphate of potash when heated with 
hydrate of potash, when they acquire the elements of water. 

AKSENIC. 

As = 75 parts by weight.* 

171. This element is often classed among the metals, because it has a 
metallic lustre and conducts electricity, but it is not capable of forming a 
base with, oxygen, and the chemical character and composition of its 
compounds connect it in the closest manner with phosphorus. 

* The specific gravity of the vapour of arsenic, like that of phosphorus, indicates that 
75 parts by weight only occupy half a volume. 



240 EXTRACTION OF ARSENIC. 

In its mode of occurrence in nature it more nearly resembles the 
sulphur group of elements, for it is occasionally found in the uncombined 
state (native arsenic), but far more abundantly in combination with 
various metals, forming arsenides, which frequently accompany the sul- 
phides of the same metals. The following are some of the chief arsenides 
and arsenio-sulphides found in the mineral kingdom : — 

Kupfernickel, NiAs . 

Arsenical nickel, NiAs 2 . 

Tin- white cobalt, CoAs 2 . 

Mispickel or arsenical pyrites, FeS 2 . FeAs 2 . 

Cobalt-glance, • CoS 2 . CoAs 2 . 

Nickel-glance, MS 2 . NiAs 2 . 

But arsenic also occurs, like the metals, in combination with sulphur, 
thus we have — 

Red orpiment or realgar, As 2 S 2 . 

Yellow orpiment, As 2 S 3 . 

It is from these minerals that arsenic derives its name (apa-a/LKov, orpiment), 
and the sulphides of arsenic being sulphur-acids, are found in combination 
with other sulphides; thus red silver ore is a compound of the sulphides 
of silver and arsenic (3Ag 2 S.As 2 S 3 ) ; Tennantite contains sulphide of 
arsenic combined with the sulphides of iron and copper ; and grey copper 
ore is composed of sulphide of arsenic with the sulphides of copper, silver, 
zinc, iron, and antimony. In an oxidised form arsenic is found in condur- 
rite, which contains arsenious acid (As 2 3 ) and suboxide of copper. 
Cobalt-bloom consists of arseniate of cobalt (3CoO.As 2 5 ). 

Arsenical pyrites is one of the principal sources of arsenic and its com- 
pounds, though a considerable quantity is also obtained in the form of 
arsenious acid as a secondary product in the working of certain ores, 
especially those of copper, tin, cobalt, and nickel. 

The substance used in the arts under the name of arsenic is really the 
oxide of arsenic or arsenious acid (As 2 3 ) ; pure arsenic itself has very few 
useful applications, so that it is not the subject of an extensive manufac- 
ture. It can be extracted from arsenical pyrites (FeS 2 .FeAs 2 ) by heating 
it in earthen cylinders fitted with iron receivers, in which the arsenic con- 
denses as a metallic-looking crust, the heat expelling it from the pyrites 
in the form of vapour. 

On a small scale it may be obtained by heating a mixture of arsenious acid with 
half its weight of recently calcined charcoal in a crucible (fig. 227), the mixture 

being covered with two or three inches of char- 
coal in very small fragments, and the crucible so 
placed that this charcoal may be heated to red- 
ness first, in order to ensure the reduction of any 
arsenious acid which might escape from below. 
In order to collect the arsenic, another crucible, 
having a small hole drilled through the bottom 
for the escape of gas, is cemented on to the first, 
in an inverted position, with fire-clay, and pro- 
tected from the fire by an iron plate with a hole 
in it for the crucible. The reduction of arsenious 
acid by charcoal is thus represented — 

As 2 3 + C 3 = As 2 + 3CO. 

For the sake of illustration, a small quantity 
of arsenic may be prepared from arsenious acid 
Fig. 227. -Extraction of arsenic. h Y a method commonly employed in testing for 

that substance. A small tube of German glass 
is drawn out to a narrow point (A, fig. 228), and sealed with the aid of the blow- 




ARSENIOUS ACID. 



241 



pipe. A very minute quantity of arsenious acid is introduced' into the point of the 
tube, and a few fragments of 
charcoal are placed in the tube 
itself at B. The charcoal is 
heated to redness with a blow- 
pipe flame, and the point is 
then heated so as to drive the 
arsenious acid in vapour over 
the red-hot charcoal, when a 
shining black ring of arsenic 
(C) will be deposited upon the 
cooler portion of the tube. 

The arsenic thus obtained 
is a brittle mass of a dark 
steel-grey colour and bril- 
liant metallic lustre (sp. gr 




Fig. 228. 



Reduction of arsenious acid. 

5*7). It does not fuse when heated, unless 
in a sealed tube, since it is converted into vapour at 356 F. It is not 
changed by exposure to air, unless powdered and moistened, when it is 
slowly converted into arsenious acid. When heated in air, it oxidises 
rapidly at about 160° F., giving off white fumes of arsenious acid and a cha- 
racteristic garlic odour (recalling that of phosphorus). At a red heat it 
burns in air with a bluish white flame, and in oxygen with great bril- 
liancy. It is not dissolved by water or any simple solvent (herein 
resembling the metals), but is oxidised and dissolved by nitric acid. 

In its chemical relations to other elements, arsenic much resembles 
phosphorus, undergoing spontaneous combustion in chlorine, and easily 
combining with sulphur. Like phosphorus also, it combines with many 
metals, even with platinum, to form arsenides, and its presence often 
affects materially the properties of the useful metals. There are some 
reasons for believing in the existence of two allotropic forms of arsenic 
differing in chemical activity like those of phosphorus. 

Pure arsenic does not produce symptoms of poisoning till a considerable 
period after its administration, being probably first oxidised in the stomach 
and intestines, and converted into arsenious acid. 



Oxides of Arsenic. - 

172. Arsenic forms two well-defined acids with oxygen, corresponding 
to phosphorous and phosphoric acids. 





Formula. 


By Weight. 


Arsenic. 


Oxygen. 


Arsenious acid, 
Arsenic acid, 


As 2 3 
As 2 5 


150 
150 


48 
80 



Arsenious Acid (As 2 3 - 198 parts by weight = l vol. = l vol. As + 
3 vols. 0)*. — Unlike phosphorus, arsenic, when burning in air, only com- 
bines with three atoms of oxygen. Arsenious acid, or white arsenic, is ^ a 
very useful substance in many branches of industry. It is employed in 
the manufacture of glass, of several colouring-matters, and of shot. A 
large quantity is also consumed for the preparation of arsenic acid and 

* The specific gravity of arsenious acid vapour is 19 S times that of hydrogen, instead of 
94 times, according to the usual law. 

Q 



242 ARSENIOUS ACID. 

arseniate of soda; it is, indeed, the source from which nearly all the 
compounds of arsenic are procured. Small quantities of crystalline 
arsenious acid are occasionally found associated with the ores of nickel 
and cobalt. 

Arsenious acid is manufactured by roasting the arsenical pyrites, chiefly 
obtained from the mines of Silesia, in muffles or ovens, through which 
air is allowed to pass, when the arsenic is converted into arsenious acid, 
and the sulphur into sulphurous acid, which are conducted into large 
chambers, in which the arsenious acid is deposited as a very fine powder. 
The iron of the pyrites is left partly as oxide, and partly as sulphate of 
iron. The removal of the arsenious acid from the condensing chambers 
is a very unwholesome operation, owing to its dusty and very poisonous 
character. The workmen are cased in leather, and protect their mouths 
and noses with damp cloths, so as to avoid inhaling the fine powder. 

This rough arsenious acid is subjected to a second sublimation on a 
smaller scale in iron vessels, when it is obtained in the form of a semi- 
transparent glassy mass known as vitreous arsenious acid, which gradually 
becomes opaque when kept, and ultimately resembles porcelain. The 
white arsenic sold in the shops is a fine powder, dangerously resembling 
flour in appearance, but so much heavier (sp. gr. 3*7) that it ought not to 
be mistaken for it. . When examined under the microscope, it appears in 
the form of irregular glassy fragments, mixed with octahedral crystals. 
Arsenious acid softens when gently heated, but does not fuse (unless in a 
sealed tube), being converted into vapour at 380° E., and depositing in 
brilliant octahedral crystals upon a cool surface. The experiment may be 
made in a small tube sealed at one end, the upper part of which should 
be slightly warmed before heating the arsenious acid, so as to prevent too 
rapid condensation, which is unfavourable to the formation of distinct 
crystals.* The octahedra are best examined with a binocular microscope. 
This common poison may fortunately be still more easily recognised by 
sprinkling it upon a red-hot coal, when a strong odour of garlic is percep- 
tible, due to the reduction of the acid by the heated carbon ; the vapour 
of arsenious acid itself is inodorous. The sparing solubility of arsenious 
acid in water is very unfavourable to its action as a poison, for, when 
thrown into ordinary liquids, it is dissolved in very small quantity, the 
greater part of it collecting at the bottom. Even when arsenious acid is 
taken into the stomach in a solid state, its want of solubility delays its 
passage into the blood sufficiently to give a better chance of antidotal 
treatment than in the case of most other common poisons. Its compara- 
tive insolubility is shown by its being almost tasteless. 

When thrown into water, arsenious acid exhibits great repulsion for 
the particles of that liquid, and collects in a characteristic manner round 
little bubbles of air, forming small white globes which are not wetted by 
the water. Even if the acid be stirred with the water, and allowed to 
remain in contact with it for some hours, a pint of water (20 oz.) would 
not take up more than 20 grs. of arsenious acid. The smallest dose which 
has been known to prove fatal is 2*5 grs. If boiling water be poured 
upon powdered arsenious acid, and allowed to remain in contact with it 
till cold, it will dissolve about T ^ of its weight (22 grs. in a pint). 

When powdered arsenious acid is boiled with water for two or three 

* When arsenious acid is fused in a long tube, sealed at both ends, and buried in hot 
sand, the mass, after cooling, is found to contain some prismatic crystals, which are also 
sublimed on those parts of the tube which have been heated above 390° F. 



ARSENITES. 243 

hours, 100 parts by weight of water may be made to dissolve 11*5 parts 
of the acid, and when the solution is allowed to cool, about 9 parts of the 
acid will be deposited in octahedral crystals, leaving 2*5 parts dissolved 
in 100 of water (219 grs. in a pint). 

This great increase in the solubility of the arsenious acid by long boiling 
with water, is usually attributed to the conversion of the opaque or crys- 
talline variety of the acid, which always composes the powder, into the 
vitreous modification, which is the more soluble in water. Water, heated 
with arsenious acid in a sealed tube, may be made to dissolve its own 
weight of the acid ; as the solution cools, it first deposits prismatic crystals, 
and afterwards the ordinary octahedral form. The solution of arsenious 
acid is very feebly acid to blue litmus paper. 

Arsenious acid dissolves abundantly in hot hydrochloric acid (a part of 
it being converted into terchloride of arsenic), and as the solution cools, 
part of the acid is deposited in large octahedral crystals. It is said that 
if the vitreous acid be dissolved in hydrochloric acid, the formation of 
these crystals will be attended by flashes of light, visible in a darkened 
room ; but the opaque variety does not exhibit this phenomenon. 

The vitreous arsenious acid has a slightly higher specific gravity than 
the opaque form, and fuses rather more easily. The opaque variety appears 
to be identical in its properties with crystallised arsenious acid. 

Solutions of the alkalies readily dissolve arsenious acid, forming alkaline 
arsenites, the solutions of which are capable of dissolving arsenious acid 
more easily than water, and deposit it in crystals on cooling. Arsenious 
acid is sometimes deposited in prismatic crystals from its solution in 
potash, and the same form of crystallised arsenious acid has been found 
native. On adding a small quantity of hydrochloric acid to the solution 
of the alkaline arsenite, a white precipitate of arsenious acid is formed. 

Arsenious acid has the property of preventing the putrefaction of skin 
and similar substances, and is occasionally employed for the preservation 
of objects of natural history, &c. 

Arsenites. — Arsenious acid does not destroy the alkaline reaction of the 
alkalies, and it does not decompose the alkaline carbonates unless heat is 
applied, proving it to be a feeble acid. The arsenite of ammonia is very 
unstable, evolving ammonia freely when exposed to the air. When 
arsenious acid is dissolved in a hot solution of ammonia, octahedral crys- 
tals of the acid are deposited on cooling, notwithstanding the presence of 
ammonia in large excess. 

When the carbonates of potasli and soda are fused with an excess of 
arsenious acid, brilliant transparent glasses are obtained which are similar 
in composition to glass of borax (K.O^As^Og and Na. 2 0.2As 2 O s ). 

If an alkaline arsenite' be fused in contact with platinum, the latter is 
easily melted, combining with a small proportion of arsenic to form a 
fusible arsenide of platinum, a portion of the arsenious acid being con- 
verted into arsenic acid ; 5 As 2 3 = 3As 2 5 + As 4 . The alkaline arsen- 
iates are so much more stable than the arsenites, that the latter exhibit a 
great tendency to pass into the former, with separation of arsenic. 

In consequence of the feeble acid character of arsenious acid, and the 
want of stability of the alkaline arsenites, there is some difficulty in ascer- 
taining whether it is a monobasic acid or otherwise. The arsenite of 
silver (3Ag 2 O.As,0 3 ), however, contains 3 molecules of oxide of silver 
combined with 198 parts of arsenious acid; and arsenite of zinc 
(3ZnO.As 2 3 ) contains 3 molecules of oxide of zinc combined with 198 



244 



ARSENIC ACID. 



parts of arsenious acid. Moreover, the arsenite of magnesia, dried at 
400° F., has the composition 2MgO.H 2 O.As 2 3 , so that arsenious acid 
would appear to resemble boracic acid, in requiring 3 molecules of potash 
or soda to form a completely saturated compound. No compound of the 
anhydrous acid with water or its elements has yet been obtained. 

The arsenites of potash and soda in solution are sometimes employed 
as sheep-dipping compositions ; and an arsenical soap, composed of arsenite 
of potash, soap, and camphor, is used by naturalists to preserve the skins 
of animals. Arsenite of soda is also occasionally employed for preventing 
incrustations in steam-boilers, being prepared for that purpose by dissolving 
2 molecules of arsenious acid in 1 molecule of carbonate of soda. 

ScJieele's green is an arsenite of copper (2CuO.H 2 O.As 2 3 ) prepared by 
dissolving arsenious acid in a solution of carbonate of potash, and decom- 
posing the arsenite of potash thus produced by adding sulphate of copper, 
when the arsenite of copper is precipitated. This poisonous colour is 
used to impart a bright green tint to paper hangings, and is sometimes 
injurious to the health of the occupants of rooms thus decorated, since 
the arsenite of copper is often easily rubbed off the paper, and diffused 
through the air in the form of a fine dust, a small portion of which is 
inhaled with every breath. 

The presence of the arsenite of copper in a sample of such paper is readily proved 

by soaking it in a little ammonia, which 
will dissolve the arsenite of copper to a 
blue liquid, the presence of arsenic in 
which may be shown by acidifying it 
with a little pure hydrochloric acid, and 
boiling with one or two strips of pure 
copper, which will become covered with 
a steel-grey coating of arsenide of cop- 
per. On washing the copper, drying it 
on filter-paper, and heating it in a small 
tube (fig. 229), the arsenic will be con- 
verted, into arsenious acid, which will 
deposit in brilliant octahedral crystals on 
the cool part of the tube. It is obvious 
that, to avoid mistakes, the ammonia, 
hydrochloric acid, and copper should be examined in precisely the same way, with- 
out the suspected paper, so as 'to render it certain that the arsenic is not derived from 
them. 

The effective green colour of the arsenite of copper also leads to its 
employment as a colour for feathers, muslin, &c, where it is very inju- 
rious to the health of the work-people. It has even been ignorantly or 
recklessly used for colouring twelfth-cake ornaments, &c. 

In quantities short of poisonous doses, arsenious acid appears to have a 
remarkable effect upon the animal body. Grooms occasionally employ it 
to improve the appearance of horses, and in Styria it seems to be taken 
by men and women for the same purpose, apparently favouring the secre- 
tion of fat. It is said that a continuance of the custom developes a 
craving for this drug, and enables large doses to be taken without imme- 
diate danger, though the ultimate consequences are very serious. 

Solution of arsenite of potash (Fowler's solution) has long been used in 
medicine. 

173. Arsenic acid (As 2 O 5 = 230 parts by weight). — This acid has 
acquired great importance in the chemical arts during the last few years, 
having been employed to replace the expensive tartaric acid used in 




Fig. 229. 



ARSENIETTED HYDROGEN. 245 

calico-printing, and to furnish, by its action upon aniline, the magnificent 
dye known as Magenta. 

Arsenic acid is prepared by oxidising arsenious acid with three-fourths 
of its weight of nitric acid of sp. gr. 1*35, when it dissolves with evolution 
of much heat and abundant red fumes of nitrous acid — 

As 2 3 + H 2 Q.N 2 5 + 2H 2 - N 2 3 + 3H 2 O.As 2 5 . 

After cooling, the solution deposits very deliquescent prismatic crystals 
containing 3H 2 O.As 2 5 .Aq. When these are heated to 212° F. they 
melt, and the liquid gradually deposits needle-like crystals of trihydrated 
arsenic acid, 3H 2 O.As 2 5 , corresponding to common or tribasic phosphoric 
acid. At 300° F. the hydrate 2H 2 O.As 2 5 may be obtained, and at a 
temperature of 500° F. a white mass of anhydrous arsenic acid (As 2 5 ) is 
left. If this be heated to redness, it fuses and is decomposed into arsen- 
ious acid and oxygen. 

The hydrates of arsenic acid have acquired unusual importance, in conse- 
quence of a costly trial, in the law courts, of the question, whether the 
patent for Magenta dye could be pronounced invalid because the patentee 
had described it as being producible by the action of dry arsenic acid 
upon aniline ; whereas the anhydrous acid, acting upon aniline, will not 
furnish the colour, though either of the solid (and therefore dry in popular 
language) hydrates will do so. The patent was eventually invalidated, 
though not merely upon this question. 

Anhydrous arsenic acid has very much less attraction for water than 
the anhydrous phosphoric acid to which it corresponds ; it deliquesces 
slowly in air, and dissolves rather reluctantly in water. Neither does it 
appear that its combinations with water differ from each other, like the 
phosphoric acids, in the salts to which they give rise, arsenic acid forming 
tribasic salts only, like common phosphoric acid. The arseniates cor- 
respond very closely to the tribasic phosphates with which they are 
isomorphous (i.e., identical in crystalline form). Thus the three arseniates 
of soda are similar in composition to the three tribasic phosphates of 
soda, their formulae being 3Na 2 O.As 2 5 .24A.q. ; 2Na 2 O.H 2 O.As 2 5 .24Aq. ; 
and JSfa 2 0.2H 2 0. As 2 5 . Aq. But if the two last salts be heated, they lose 
their basic water without giving rise to new salts corresponding to the 
pyrophosphate and metaphosphate of soda, and resume their former con- 
dition when placed in contact with water. 

The common arseniate of soda (2Na 2 O.H 2 O.As 2 5 .14Aq.) is largely 
used by calico printers as a substitute for the dung-baths formerly em- 
ployed, since, like the common phosphate of soda, it possesses the feebly 
alkaline properties required in that particular part of the process. It is 
manufactured by combining arsenious acid with soda, and heating the 
resulting arsenite of soda with nitrate of soda, from which it acquires 
oxygen, becoming converted into arseniate of soda. 

Arsenic acid is a much more powerful acid than arsenious acid, being 
comparable, in this respect, with phosphoric acid. It appears to be less 
poisonous than arsenious acid. 

174. Arsenietted hydrogen (AsH 3 = 78 parts by weight = 2 vols. = 
J vol. As + 3 vols. H). — The only compound of arsenic and hydrogen, 
the existence of which has been satisfactorily established, is that which 
corresponds to ammonia and phosphuretted hydrogen gas, and is repre- 
sented by the formula, AsH^. It is prepared by the action of sulphuric 



246 



MARSH S TEST FOE ARSENIC. 



acid diluted with three parts of water upon the arsenide of zinc, obtained 
by heating equal weights of zinc and arsenic in an earthen retort; 
Zn ? As 2 + 3(H 2 O.S0 3 ) = 2AsH 3 + 3(ZnO.S0 3 ). The gas is so poisonous 
in its character that its preparation in the pure state is attended with 
danger. It has a sickly alliaceous odour, and may be liquefied at — 40° 
F. It is inflammable, burning with a peculiar livid flame, producing 
water and fumes of arsenious acid ; 2AsH 3 + 6 = As 2 3 + 3H 2 0. The 
chief interest attaching to this gas depends upon the circumstance that its 
production allows of the detection of very minute quantities of arsenic in 
cases of poisoning. 

The application of this test, known as Marsh's test, is the safest method of prepar- 
ing arsenietted hydrogen in order to study its properties, for it is obtained so largely 
diluted with free hydrogen that it ceases to be so very dangerous. Some fragments 
of granulated zinc are introduced into a half-pint bottle 
(fig. 230), provided with a funnel-tube (A), and a narrow tube 
(B) bent at right angles and drawn out to a jet at the extremity ; 
this tube should be made of German glass, so that it may not 
fuse easily. The bottle having been about one-third filled 
with water, a little diluted sulphuric acid is- poured down the 
funnel-tube so as to cause a moderate evolution of hydrogen, 
and after about five minutes (to allow the escape of the air) 
the hydrogen is kindled at the jet. If a few drops of a solu- 
tion obtained by boiling arsenious acid Avith water be now 
poured down the funnel, arsenietted hydrogen will be evolved 
together with the hydrogen — 

As 2 3 + Zn 6 + 6(H 2 O.S0 3 ) = 2AsH 3 + 6(ZnO.S0 3 ) + 3H. 2 . 




Fig. 230. 



Fig. 231. 



The hydrogen flame will now acquire the livid hue above referred to, and a white 
smoke of arsenious acid will rise from it. If a piece of glass or 
porcelain be depressed upon the flame (fig. 231), it will acquire 
a metallic-looking coating of arsenic, just as carbon would be 
deposited from an ordinary gas-flame. Arsenietted hydrogen 
is easily decomposed by heat, so that if the glass tube 
through which it passes be heated with a spirit-lamp (fig. 232), 
a dark mirror of arsenic will be deposited a little in front of the heated part, and 

the flame of the gas will lose its livid hue. These 
deposits of arsenic are extremely thin, so that a 
very minute quantity of arsenic is required to 
form them, thus rendering the test one of extra- 
ordinary delicacy. It must be remembered, how- 
ever, that both sulphuric acid and zinc are liable 
to contain arsenic, so that erroneous results may 
be very easily arrived at by this test in the hands 
of any but those specially devoted to such investi- 
gations. 

Arsenietted hydrogen, like sulphuretted hydro- 
gen, causes dark precipitates in many metallic 
solutions. 

Phosphuretted hydrogen, arsenietted hy- 
drogen, and ammonia, constitute a group of 
hydrogen compounds having certain pro- 
perties in common, which distinguish them from, the compounds of 
hydrogen with other elements. 

Two volumes of each of these gases contain three volumes of hydrogen. 
They are all possessed of peculiar odours, that of ammonia being the 
most powerful, and that of arsenietted hydrogen the least. 

Ammonia is powerfully alkaline, phosphuretted hydrogen exhibits 
some tendency to play an alkaline part, whilst arsenietted hydrogen seems 
devoid of alkaline disposition. 




Fig. 232. 



TERCHLORIDE OF ARSENIC. 



247 



All these are inflammable, ammonia being the least so of the group ; 
and all are decomposed by heat, ammonia least easily, and arsenietted 
hydrogen most easily. 

They are all producible from their corresponding oxygen compounds, 
viz., N 2 O a , P 2 3 , and As 2 3 , by the action of nascent hydrogen (e.g., by 
contact with zinc and diluted sulphuric acid). 

All three are the prototypes of various organic bases whieh contain 
some compound radical in place of the hydrogen, thus — 



NH 3 is the prototype of triethylamine, 
PH., ,, ,, triethylphosphine, 



AsH. 



triethylarsine, 



^(C 2 H 5 ) 3 
As(C 2 H 5 ), 




Fig. 233. 



175. Terchloride of arsenic. — Only one compound of chlorine with arsenic (AsC] 3 ) 
has yet been obtained ; the chloride corresponding to pentachloride of phosphorus 
remains to be discovered.* The ter- 
chloride may be formed by the direct 
union of its elements, but the simplest 
laboratory process for procuring it con- 
sists in heating arsenious acid in dry 
chlorine gas, in a tubulated retort 
(A, fig. 233). extemporised from a 
Florence flask (see p. 103). The arse- 
nious acid soon melts, and the ter- 
chloride of arsenic distils over, leaving 
a melted mass in the flask, which 
forms a brilliantly transparent glass on 
cooling, the composition of which 
varies somewhat with the temperature 
employed, but appears to be essentially 
2As 2 3 . As 2 5 . The same vitreous com- 
pound may be obtained by fusing 
arsenious and arsenic acids together. 
The formation of the terchloride of arsenic may be represented by the equation, 
HAs 2 3 + Cl 12 = 4AsCl 3 + 3(2As 2 3 .As 2 5 ). 

Terchloride of arsenic bears a great general resemblance to terchloride of phos- 
phorus ; it is a heavy (sp. gr. 2 - 2), pungent, fuming liquid, decomposed by the 
moisture of the air, its vapours depositing a white coating of arsenious acid upon the 
objects in its immediate neighbourhood. When poured into water it deposits 
arsenious acid ; 2AsCl 3 + 3H 2 = As 2 3 + 6HC1 ; but when dissolved in the smallest 
possible quantity of water, it deposits crystals of the formula AsOCl.H 2 0. 

"When arsenious acid is dissolved in hydrochloric acid, terchloride of arsenic is 
formed, As 2 3 + 6HC1 = 2AsCl 3 + 3H 2 0, and remains undecomposed by the water 
in the presence of strong hydrochloric acid, but if water be added, arsenious acid is 
precipitated. "When the solution of arsenious acid in hydrochloric acid is distilled, 
the terchloride of arsenic distils over, and this is sometimes a convenient method of 
separating arsenic from articles of food, &c. , in testing for that poison. When heated 
in dry hydrochloric acid gas, arsenious acid yields a glassy compound, which contains 
As 2 3 .AsC10 ; 3As 2 3 + 2HC1 = 2(As 2 3 .AsC10) + H 2 0. 

In composition by volume, the terchloride of arsenic resembles terchloride of 
phosphorus, containing \ vol. of arsenic vapour, and 3 vols, of chlorine condensed 
into 2 vols., the specific gravity of its vapour being 6*3. 

Terbromide of arsenic much resembles the terchloride in its chemical characters, 
but is a solid crystalline substance, easily fusible. 

1 76. Teriodide of arsenic (Asl 3 ) is remarkable for not being decomposed by water, 
like the corresponding phosphorus compound. When obtained by heating arsenic 
and iodine together, it sublimes in brick-red flakes, which, if prepared on a large scale, 
hang in long laminee like sea-weed. It may be dissolved in boiling water, and 
crystallises out unchanged. It may even be prepared by heating 3 parts of arsenic 

* Nickles appears to have siicceeded in forming the pentachloride by the action of hydro- 
chloric acid gas on arsenic acid in presence of ether ; he describes it as very unstable, and 
easily converted into the terchloride. 



248 REALGAR— ORPIMENT. 

with 10 of iodine and 100 of water, when the solution deposits red crystals of the 
hydrated teriodide, from which the water may be expelled by a gentle heat. 

The terfiuoricle of arsenic (AsF s ) resembles the terchloride, but is much more 
volatile. It may be obtained by distilling 4 parts of arsenious acid with 5 of fluor- 
spar and 10 of strong sulphuric acid in a leaden retort (see p. 181). It does not 
attack glass unless water be present, which decomposes it into arsenious and hydro- 
fluoric acids. 

177. Sulphides op arsenic. — There are three well-known sulphides of 
arsenic, having the composition As 2 S 2 , As 2 S 3 , and As 2 S 5 , the two former 
being found in nature. 

Realgar (As 2 S 2 ) is a beautiful mineral, crystallised in orange-red prisms ; 
but the red orpiment used in the arts is generally prepared by heating a 
mixture of arsenious acid and sulphur, when sulphurous acid escapes, and 
an orange-coloured mass of realgar is left — 

2As 2 3 + S 7 = 2As 2 S 2 + 3S0 2 . 

Another process for preparing it consists in distilling arsenical pyrites 
with sulphur or with iron pyrites — 

FeS 2 .FeAs 2 + 2EeS 2 = 4FeS + As 2 S 2 . 

Arsenical pyrites. Iron pyrites. -P * e ° Realgar. 

The realgar distils over, and condenses to a red transparent solid. 
Eealgar burns in air with a blue flame, yielding arsenious acid and sul- 
phurous acid. If it be thrown into melted saltpetre, it burns with a 
brilliant white flame, being converted into arseniate and sulphate of 
potash. This brilliant flame renders realgar an important ingredient in 
Indian fire and similar compositions for fire-works and signal lights. A 
mixture of one part of red orpiment with 3 '5 parts of sublimed sulphur 
and 1 4 parts of nitre is used for signal-light composition. 

Realgar is not easily attacked by acids ; nitric acid, however, dissolves it, with the 
aid of heat, forming arsenic acid and sulphuric acid, with separation of part of the 
sulphur in the free state. Alkalies (potash, for example) partly dissolve it, leaving 
a brown substance, which appears to be a subsulphide of arsenic (As 12 S). 

Yellow orpiment, or tersulphide of arsenic (As 2 S 3 ), is found native in 
yellow prismatic crystals. The paint known as King's yellow is a mix- 
ture of tersulphide of arsenic and arsenious acid, prepared by subliming 
a mixture of sulphur with arsenious acid — 

S 9 + 2As 2 3 = 2As 2 S 3 + 3S0 2 . 

It is, of course, very poisonous. 

This substance, like realgar, is not much affected by acids, excepting nitric acid ; 
but it dissolves entirely in potash, forming arsenite of potash and sulpharsenite of 
(sulphide of) potassium ;12KHO + 2As 2 S 3 = 3K 2 S.As 2 S 3 + 3K 2 O.As 2 3 + 6H 2 0. 
Ammonia also dissolves it easily, forming a colourless solution which is employed 
for dyeing yellow, since if a piece of stuff be dipped into it and exposed to air, the 
ammonia will volatilise, leaving the yellow orpiment behind. 

The formation of the characteristic yellow tersulphide is turned to account in test- 
ing for arsenic ; if a solution prepared by boiling arsenious acid with distilled water 
be mixed with a solution of hydrosulphuric acid, a bright yellow liquid is produced, 
which looks opaque by reflected, but transparent by transmitted light, and may be 
passed through a filter without leaving any solid matter behind. This solution pro- 
bably contains a soluble compound of tersulphide of arsenic with hydrosulphuric acid 
(3H 2 S.As 2 S 3 ) ; it is, however, very unstable, being decomposed by evaporation, with 
precipitation of the tersulphide. The addition of a little hydrochloric acid, or of 
sal-ammoniac, and many other neutral salts, will also cause a separation of the ter- 



REVIEW OF THE NON-METALLIC ELEMENTS. 249 

sulphide from this solution ; even the addition of a hard water will have that effect. 
If the solution of arsenious acid be acidified with hydrochloric acid before adding 
the hydrosulphuric acid, the bright yellow tersulphide of arsenic is precipitated 
at once, and may be distinguished from any other similar precipitate by. its ready 
solubility in solution of carbonate of ammonia. 

From its combining readily with the alkaline sulphides to form soluble com- 
pounds, the tersulphide of arsenic is often called sulpharsenious acid. 

Pentasulphide of arsenic (As 2 S 5 ), or sulpharsenic acid, possesses far less practical 
importance than the preceding sulphides ; it may be obtained by fusing the tersul- 
phide with sulphur, when it forms an orange-coloured glass, easily fusible, and 
capable of being sublimed without change. When hydrosulphuric acid gas is passed 
through solution of arsenic acid, a white precipitate of sulphur is first obtained, the 
hydrogen reducing the arsenic acid to arsenious acid ; As 2 5 + 2H 2 S = As 2 3 + 
2H 2 + S 2 ; and if the passage of the gas be continued, the arsenious acid is decom- 
posed, and tersulphide of arsenic is precipitated ; these changes are much accelerated 
by heat. But if a solution of arseniate of soda be saturated with hydrosulphuric acid, 
it is converted into sulpharseniate of (sulphide of) sodium — 

2Na 2 O.H 2 O.As0 5 + 7H 2 S = 8H 2 + 2Na 2 S.As 2 S 5 . 

On adding hj^drochloric acid to this solution, a bright yellow precipitate of penta- 
sulphide of arsenic is obtained — 

2Na 2 S.As 2 S 5 + 4HC1 = 4NaCl + 2H 2 S + As 2 S 5 . 

Pentasulphide of arsenic is one of the most powerful of the sulphur acids ; it 
expels hydrosulphuric acid from its combinations with the alkaline sulphides, and 
is capable of forming, with these, sulpho-salts, containing respectively one, two, and 
three molecules of the alkaline sulphide, which may be obtained by the action of 
hydrosulphuric acid upon the corresponding arseniates. 



GENEKAL EEVIEW OF THE NON-METALLIC ELEMENTS. 

178. At the conclusion of the history of the non-metals, it may "be 
well to call attention to the points of resemblance which classify them 
into separate groups or families, most of which are connected, by some 
analogies, with one or more members of the class of metals. 

Hydrogen stands alone among the non-metals, its chemical properties 
and functions being widely different from those of any other non-metal, 
but connecting it very closely with the most highly electropositive (or 
basylous) metals, such as potassium and sodium. 

Oxygen, Sulphur, Selenium, and Tellurium compose a group, the mem- 
bers of which (in the state of vapour) combine with twice their volume 
of hydrogen to form compounds which (in the state of vapour) occupy 
. the same volume as the hydrogen occupied before combination. All these 
hydrogen compounds are capable of playing a feebly acid part, and their 
hydrogen may be displaced by an equivalent weight of a metal to produce 
compounds exhibiting a general agreement in chemical properties. This 
group is connected with the metals through tellurium, not only by its 
physical properties, but by its forming an oxide (Te0 2 ), which occasion- 
ally acts as a weak base. 

Nitrogen, Phosphorus, and Arsenic are connected together by the gene- 
ral analogy of their hydrogen and oxygen compounds, the two last mem- 
bers of the group being far more closely connected with each other than 
with nitrogen. With the metals, they are connected through arsenic, the 
hydrogen compound of which is very similar in properties, and probably 
in composition, to antimonietted hydrogen ; arsenious acid (As 2 3 ) is also 
capable of occupying the place of teroxide of antimony (Sb 2 3 ) in certain 
salts of that oxide ; and the sulphides of antimony correspond in composi- 



250 CLASSIFICATION ACCORDING TO ATOMICITY. 

tion, and in some of their properties, to those of arsenic. One form of 
arsenious acid (the prismatic) is isomorphous with native oxide of anti- 
mony, and this oxide may be obtained in octahedra, the ordinary form of 
arsenious acid, so that these oxides are isodimorphous. 

These elements are also connected with the oxygen group through 
sulphur, selenium, and tellurium, the relations of which to hydrogen and 
the metals are somewhat similar to those of phosphorus and arsenic. 

Carbon, Boron, and Silicon resemble each other in their allotropic 
forms, their resistance to fusion and volatilisation, and their forming 
feeble acids with oxygen. To the metals they are allied through silicon, 
which resembles tin in the composition and character of its oxide and 
chloride. 

This group is connected with the nitrogen group through boron, for 
boracic acid resembles arsenious acid in its relations to bases, and in 
forming vitreous compounds with the alkalies. In certain compounds 
boracic and arsenious acids are interchangeable. 

Chlorine, Bromine, Iodine, and Fluorine are intimately connected by 
numerous analogies, which have been already pointed out (p. 186). Some 
of the properties of iodine, as its relations to oxygen, and the solubility 
of its terchloride in water, connect it slightly with the metals, whilst the 
general correspondence in composition between the chlorides and the 
oxides, allies this group to the oxygen group of non-metallic elements. 

If the non-metals be classified according to their quanti valence (see p. 
158), it will be found that, with only few exceptions, the classification 
will coincide with that founded upon their chemical analogies in other 
respects. Thus, the members of the oxygen group are all diatomic, or 
capable of combining with two atoms of hydrogen, as shown by the 
formulae of their hydrogen compounds, H 2 0, H 2 S, H 2 Se, H 2 Te. The 
nitrogen group is generally represented as triatomic, (though, from our 
present knowledge of the vapour densities of phosphorus and arsenic, 
these elements are strictly hexatomic,) their hydrogen compounds being 
NH 3 , PH 3 , and AsH 3 . Boron is also a triatomic element, for, in BCl oJ 
the boron occupies the place of three atoms of hydrogen. 

Carbon and silicon, however, are tetratomic elements, as shown in 
marsh-gas, CH 4 , and in chloride of silicon, SiCl 4 . 

Chlorine, bromine, iodine, and fluorine are monatomic, their hydrogen 
compounds having the formulas, HC1, HBr, HI, and HF. 

The atomicity or quantivalence of an element is sometimes expressed 
in a formula by a dash, or dashes, placed above and to the right of the 
element; thus the symbols, CI', 0", W\ C"", indicate the respective 
atomicities of those elements. When the atomicity of an element is 
taken into account, it helps to explain the constitution of compounds 
which would otherwise appear quite anomalous. For example, there is a 
compound of the molecular formula, N 3 H 6 P, obtained by the action of 
terchloride of phosphorus upon ammonia; recollecting the triatomic 
character of phosphorus, we perceive this compound to represent three 
molecules of ammonia (N 3 H 9 ), in which phosphorus is the substitute for 
three atoms of hydrogen, which is at once expressed if the formula be 
written, N 3 H 6 P"'. Again, chlorocarbonic acid, C0C1 2 , appears an inex- 
plicable association of elements, until the tetratomic character of carbon 
and diatomic character of oxygen are taken into account, as in the for- 
mula C^'CCl^ when it appears that the diatomic oxygen and the two 
atoms of monatomic chlorine are the substitutes for four atoms of hydrogen 



CONSTITUTION OF SALTS. 251 

in marsh-gas, CH 4 , and it might plausibly be given as a reason why the 
apparently indifferent carbonic oxide should combine with chlorine, that 
the atomicity of the carbon is only partly satisfied in carbonic oxide, 
which contains only oxygen equal in value to two atoms of hydrogen, 
the tetratomic carbon requiring the value of two more atoms of hydrogen 
to complete the compound atom. In carbonic acid, C^'O^, the two 
atoms of diatomic oxygen fully complete the compound. 

In a similar manner the absorption of carbonic oxide by subchloride of 
copper may be explained ; for the atomic formula of that salt is Cu'Cl', 
and hence it is capable of supplying the two absent atoms in C""0". 

Many more examples of the same kind might be gathered from the 
preceding pages, but these will probably be sufficient to mark the import- 
ance of remembering the atomicities of the elements in speculative che- 
mistry ; indeed, without this clue it is impossible to find any meaning 
whatever in a very large number of the formulae of organic substances, 
whilst with it, not only their constitution, but in many cases their mode 
of formation, becomes as intelligible as that of the simplest mineral com- 
pounds. 



CONSTITUTION OF SALTS. 

179. The term salt, like acid and alkali, was, of course, purely em- 
pirical in its origin, being conferred upon every solid substance which 
exhibited any of the prominent characters of sea-salt (sal, brine, a-dXos, the 
sea), such as solubility in water and tendency to crystallisation. 

When the great mass of chemical facts accumulated by the alchemists, 
metallurgists, and apothecaries, came to be classified, and the distinction 
between acids and bases was recognised, the term salt was extended to all 
those substances, such as muriate of soda, nitrate of potash, carbonate of 
lime, &c, from which a base and an acid could be obtained, without re- 
gard to their solubility or tendency to crystallise. When the analytical 
powers of the chemist were more fully developed, it was found that 
muriate of soda and a large class of similar salts did not contain an acid 
and a base, but that these substances were ijroduced and not educed from 
the salts by the chemical operations to which they were subjected. Thus 
muriate of soda, from which muriatic acid had been so easily produced by 
the action of sulphuric acid, was shown to contain only sodium and 
chlorine. 

This led to a classification of salts into haloid salts (aAs, the sea), or 
those composed, like chloride of sodium, of a metal combined with a salt- 
radical or halogen, and oxij-acid salts, or those composed of a metallic 
oxide combined with an oxygen acid. (It will have been remarked that 
the tendency of modern chemistry is to represent this second class of 
salts by formulae which do not admit the existence of the metal as an 
oxide in the salt.) 

Independently of all differences of opinion with respect to the actual 
constitution of salts, the criterion by which the claims of a substance to 
this title can be estimated is this : a salt is a compound which may be 
formed by the action of an acid upon a base, water, which is a very general 
result of such action, being excepted. 

The oxy-acid salts soon came to be divided into neutral and acid salts, 
according to their effect upon vegetable colours and the organ of taste, 



252 NEUTRAL AND NORMAL SALTS. 

and a class of basic salts was afterwards added, when it was found that a 
neutral soluble salt sometimes became insoluble by combining with an 
additional quantity of base. 

Further investigation has shown that the neutral taste of a salt, and its 
neutrality to test-papers, depend less upon the proportions of the acid and 
base which are contained in it, than upon the chemical energy of these 
substances. 

Thus, potash combined with one molecule of sulphuric acid forms a salt 
which is perfectly neutral to taste and to litmus-papers, whilst with one 
molecule of carbonic acid it forms a strongly alkaline salt ; and one mole- 
cule of sulphuric acid combined with one molecule of oxide of zinc forms 
a salt which is strongly acid to test-papers. 

A salt may, therefore, be neutral in chemical constitution, and acid or 
alkaline in reaction to test-papers, and it has been proposed to employ the 
term normal to designate those salts which are neutral in chemical con- 
stitution, and to restrict the term neutral to those salts which are neither 
acid nor alkaline to test-papers. Thus, sulphate of potash would be both 
a neutral and a normal salt, whilst sulphate of zinc and carbonate of 
potash are normal, but not neutral salts. 

A normal salt is one in which the oxygen contained in the base bears 
a certain proportion to the oxygen contained in the acid, this proportion 
being fixed for each acid. 

Thus, a normal carbonate is one in which the oxygen of the base bears 
to the oxygen of the acid the ratio of 1:2, as in normal carbonate of 
potash, K 2 O.C0 2 . 

A normal sulphate is one in which the oxygen of the base bears to the 
oxygen of the acid the ratio of 1 : 3, as in normal sulphate of zinc 
ZnO.S0 3 . 

To form a normal salt with a sesquioxide, 3 molecules of sulphuric acid 
are required. Thus the sulphate of alumina, A1 2 3 .3S0 3 , although power- 
fully acid to test-papers, is a normal sulphate, for the oxygen of the base 
bears to the oxygen of the acid the ratio of 1 : 3. 

An acid salt is one in which the oxygen in the acid is in greater proportion 
than in the normal ratio. Thus bicarbonate of potash, K 2 O.H 2 0.2C0 2 , 
is acid in chemical constitution, though alkaline to test-papers, for the 
oxygen of the base is to the oxygen of the acid as 1 : 4, whilst the normal 
ratio for carbonates is 1 : 2. Acid salts usually have the deficiency of 
base supplied by water, but not invariably, as in fused borax, Na 2 0.2B0 3 , 
bichromate of potash K 2 0.2O0 3 , dried bisulphate of soda, Na 2 0.2S0 3 . 

A basic salt is one in which the oxygen in the base is in greater propor- 
tion than in the normal ratio. Thus, white lead, 2(PbO.C0 2 ), PbO.H 2 0, 
is a basic carbonate, for the oxygen of the base is to the oxygen of the 
acid as 3 : 4, whereas the normal ratio is 2 : 4 or 1 : 2. 

Aluminite, A1 2 3 .S0 3 .9H 2 0, is a basic salt, for the oxygen in the base 
is to the oxygen in the acid as 3 : 3, whilst the normal ratio is 1 : 3. 

In order to explain the results obtained by the actual analysis of 
salts, it may be supposed that the salts are formed upon the type of the 
hydrated acid, and that a normal salt is one in which the water in the 
hydrated acid is displaced by an equivalent quantity of base ; thus the 
sulphates are formed upon the type of oil of vitriol, H 2 O.S0 3 , and the H 2 
must be displaced by K 2 to form the normal sulphate of potash ; but 
when alumina (A1 2 3 ) is employed to displace the water, one-third of the 
quantity represented by that formula would be equivalent to the ILO (for 



BINAPtY THEORY OP SALTS. 



253 



Al 2 is equivalent to H 6 ), and therefore the normal sulphate of alumina 
would be J (A1 2 3 ).S0 3 , or avoiding the fraction, A1 2 3 .3S0 3 . 

The following are the normal ratios for some of the most important 
classes of salts : — 



Salts. 


Normal Ratio. 


Examples. 


Carbonates, . 

Borates, 

Silicates, 

Nitrates, 

Chlorates, 

Sulphites, 

Sulphates, . 

Metaphosphates, 

P yrophosph ates, 

Orthophosphates, 

Arsenites, 

Arseniates, . 

Chromates, . 

Permanganates, . 




1 
3 
2 
1 
1 
1 
1 
1 
2 
3 
3 
3 
1 
1 


2 

3? 

2 

5 

5 

2 

3 

5 

5 

5 

3? 

5 

3 

7 


Na 2 O.C0 2 Carbonate of soda. 
3MgO.B 2 3 Borate of magnesia. 
2FeO.Si0 2 Forge cinder. 
K 2 O.N 2 5 Saltpetre. 
K 2 0.C1 2 5 Chlorate of potash. 
Na 2 0. S0 2 Sulphite of soda. 
CaO.S0 3 Sulphate of lime. 
Na 2 O.P 2 5 - Metaphosphate of soda. 
2Na 2 O.P 2 O g Pyrophosphate of soda. 
3CaO.P 2 5 Bone phosphate of lime. 
3Ag 2 O.A.s 2 3 Arsenite of silver. 
3CoO.As 2 5 Cobalt bloom. 
K 2 O.Cr0 3 Chromate of potash. 
K 2 O.Mn 2 7 Permanganate of potash. 



Binary theory of the constitution of salts. — The circumstance that it is 
only the hydrogen of the hydrated acid that is displaced by the metal, 
has given rise to the binary theory of salts, according to which all acids 
and salts are constituted after the type of hydrochloric acid and chloride 
of sodium ; the acid being composed of hydrogen combined with a com- 
pound salt-radical made up of the other elements present in the acid. 
Thus, sulphuric acid (H 2 O.S0 3 ) would become H 2 ,S0 4 nitric acid, 
H,N0 3 ; metaphosphoric acid, H,P0 3 ; pyrophosphoric, H 4 ,P 2 7 ; tri- 
basic phosphoric, H 3 ,P0 4 , and their normal salts are formed by the sub- 
stitution of an equivalent quantity of a metal for the hydrogen ; neu- 
tral sulphate of potassium would be K 2 , S0 4 ; pyrophosphate of sodium, 
Na 4 ,P 2 7 ; triphosphate of calcium, Ca 3 (P0 4 ) 2 . The acid salts would be 
those in which only part of the hydrogen is displaced by a metal ; bisul- 
phate of potassium would become K,H,S0 4 , -acid pyrophosphate of 
sodium, Na 2 ,H 2 ,P 2 7 . Double salts would be those in which the hydrogen 
is displaced by different metals; thus, alum (K 2 O.S0 3 ,Al 2 3 .3S0 3 ) would 
become K 2 ,A1 2 ,4S0 4 , or KA12S0 4 ; acid phosphate of potassium and 
sodium (K 2 0,Na 2 0,H 2 0,P 2 5 ) would be K,N"a,H,P0 4 . A serious objec- 
tion to this view is, that it overlooks radicals now existing (as S0 3 , 
P 2 5 , C0 2 ), and substitutes others which are not known to exist (as S0 4 , 
P0 4 , C0 3 ). 

Many chemists now represent the acids and salts by these formulae, 
without insisting upon their containing any definite compound radical, 
or being composed upon any particular type. Thus nitric acid is written 
HN0 3 , without expressing an opinion as to the existence of 3ST0 3 as an 
actual entity. 

The following definitions are relied upon by those who adopt this 
course : — 

An acid is a compound containing hydrogen, the whole or part of 
which is displaceable by a metal. 

A salt is a compound derived from an acid by the displacement of its 
hydrogen by a metal. 



254 



CONSTITUTION OF ACIDS AND SALTS. 



A monobasic acid contains but one atom of displaceable hydrogen, and 
therefore can only form one series of salts. 

A dibasic acid contains two atoms of displaceable hydrogen, and there- 
fore can form two series of salts (normal and acid salts). 

A tribasic acid contains three atoms of displaceable hydrogen, and 
therefore can form three series of salts (normal salts, and two series of 
acid salts). 

A normal salt is one in which the whole of the displaceable hydrogen 
has been displaced by a metal. 

An acid salt is one in which only part of the displaceable hydrogen 
has been displaced by a metal. 

A double salt is one in which the displaceable hydrogen has been dis- 
placed by different metals. 

A basic salt is a combination of a salt with a basic oxide. 

A few examples may be collected here to illustrate these definitions : — 



Monobasic Acids and Salts. 



Nitric Acid, . 




HN0 3 


Nitrate of potassium, . 


. 


KNO3 


Metaphosphoric acid, . 
Metaphosphate of sodium, 
Hypophosphorous acid, 
Hypophosphite of sodium, 




HP0 3 
NaP0 3 
HPH 2 2 
NaPH 2 0. 2 


Dibasic Acids and Salts. 




Sulphuric acid, 

Normal sulphate of potassium, 

Acid „. „ 


• 


H 2 S0 4 
K 2 S0 4 
KHS0 4 


Phosphorous acid, 

Normal phosphite of sodium, . 




H 2 PHO, 
Na 2 PH0 3 


Acid phosphite of barium, 




BaH 2 (PH0 3 ) 2 


Tribasic Acids and Salts. 




Orthophosphoric acid. 

Normal orthophosphate of sodium, 

Monacid orthophosphate (or common 

Diacid orthophosphate, 

Microcosmic salt, 

Arsenic acid, . 


phosphate) 


H 3 P0 4 

Na 3 P0 4 

Na 2 HP0 4 

NaH 2 P0 4 

Na(NH 4 )HP0 4 

H 3 As0 4 


Normal arseniate of sodium, 




Na 3 As0 4 


Monacid arseniate ,, 




Na 2 HAs0 4 


Diacid arseniate „ 




NaH 2 As0 4 



To this view of the constitution of acids and salts, it may be objected 
that it presupposes the existence of a hydrogen compound corresponding 
in composition to the normal salt. Thus the carbonates would be derived 
from an imaginary carbonic acid of the formula H 2 C0 3 ; the arsenites 
from an imaginary arsenious acid, H 3 As0 3 , &c. "indeed, out of the 
tiuenty-one mineral acids which are of practical importance, there are 
seven which must be thus treated in order to accommodate this theory, 
viz., carbonic (C0 2 ), nitrous (N 2 3 ), sulphurous (S0 2 ), arsenious (As 2 3 ), 
chromic (Cr0 3 ), hypochlorous (C1 2 0), and chlorous (C1 2 3 ). It must, 



WATER- TYPE THEORY OF ACIDS AND SALTS. 255 

however, be acknowledged that no theory of the constitution of acids 
and salts has yet been advanced which is thoroughly supported on all 
sides by experimental evidence. 

From what has been stated above, it will have been seen that an 
examination of the acid itself is by no means necessary in order to ascer- 
tain what its basicity is. If only one series of its salts can be discovered, 
it is a monobasic acid. If a normal and an acid salt (or a double salt) 
can be obtained, the acid is dibasic. When, beside the normal salt, there 
are two series of acid salts, the acid is tribasic. 

Water-type theory of the constitution of salts. — Another ingenious 
theory of the constitution of salts is that known as the water-type theory, 
according to which all oxygen acids are fashioned after the type of water, 
by the displacement of its hydrogen by a compound radical, such displace- 
ment being total in the anhydrous acids, and partial in the hydrated acids. 
Then, a monobasic acid is formed upon the type of one molecule of water, 
by the displacement of one atom of hydrogen to form the (hydrated) acid, 
and of both atoms to form the (anhydrous acid or) anhydride. Thus nitric 

TT ) 

acid (HN0 3 ) would be written -^-q VO, and nitric anhydride (N 2 5 ) 

would become ^r^ 2 > ; and nitrate of potassium (KN0 3 ) would 

be -^ \ ; a glance at these formulae shows why a monobasic acid 

like nitric acid does not form either acid salts or double salts, because it 
contains only one atom of hydrogen, and therefore can only form a single 
salt with each metal by displacement of that hydrogen. This view does 
not ignore the existence of the anhydrous nitric acid, and assumes, as the 
radical of the acid, the substance N0 2 , which has the composition of nitric 
peroxide. The formation of nitric acid by the action of water upon nitric 
anhydride would be thus expressed — 

H 1 n NOJ n H \ n N0 2 ) n 

In a similar manner, phosphoric anhydride (P 2 5 ) would be represented 

PO ) ~FT ) 

by -prf > 0, metaphosphoric acid (HP0 3 ) by p^ > 0, and the nieta- 

Na ) 
phosphate of sodium by p^ V 0. In this case, however, the radical P0. 2 

is, so far as we know, imaginary. 

A dibasic acid is one which is composed after the type of a double 
molecule of water, tt 2 V 2 , and therefore contains two atoms of hydro- 
gen which may be displaced either entirely by a metal, yielding a normal 
salt, or partly by a metal, yielding an acid salt, or by two metals, yielding 
a double salt. For example, sulphuric acid (H 2 O.S0 3 ) would be 

SO " \ ^ 2 ' or ^ wo m °l ecu l es of water, in which two atoms of hydrogen 

are displaced by the diatomic radical S0 2 ; normal sulphate of potassium 

80 " I ^ 2 ' ac ^ sulphate of potassium (bisulphate of potash) ^q „ > 2 

SO " ) 
and sulphuric anhydride, ^„ [■ 2 . 



256 CONSTITUTION OF POLYBASIC ACIDS. 

Here again the radical S0 2 has the same composition as sulphurous 
acid, which might well be accepted as the radical of sulphuric acid. 

CO" ) 
Again, carbonic anhydride would be p^,, > 2 , the imaginary carbonic 

acid, pX„ > 2 , carbonate of potassium, ^X„ > 2 , acid carbonate of potas- 
sium, p,y, > 2 , carbonate of potassium and sodium, p^,, V 2 . 

The radical of carbonic acid, therefore (CO), would have the same com- 
position as carbonic oxide, which is seen to have a diatomic character in 
its compound with chlorine, (COy'Cl^ where it occupies the place of two 
atoms of hydrogen. 

In applying this view to pyrophosphoric acid (2H 2 O.P 2 5 = H 4 P 2 7 ), 
some difficulty arises because its formula cannot be written on the type 
of two molecules of water (H 4 2 ) on account of the indivisibility of the 
7 into two whole numbers ; it is therefore necessary to take four mole- 
cules of water as the type, when we have — 

Type, -a- 4 }0 4 , pyrophosphoric acid, /p 4 Q y/// } 4 , pyrophosphate of 

Na ) 2 Na H ) 

sodium, ,p U y,„ !> 4 , acid pyrophosphate of sodium, ,p jk $„, > 4 . 

Here the increased complexity of the formula} appears objectionable. 

A few salts are known in which two acids are combined with the same base, such 
as the acetonitrate of baryta, composed of nitrate and acetate of baryta. It is obvious 
that the same reasoning which leads to the conclusion that an acid capable of form- 
ing a double salt with two different bases is dibasic, or contains a diatomic acid 
radical, would also support the inference that a base capable of forming a double salt 
with two different acids is di-acid, or contains a diatomic basic radical. Hence the 
existence of the above acetonitrate of baryta countenances the belief that barium is 
a diatomic metal. The formula of the salt would then be written, on the type of two 

Ba" ) 

molecules of water, thus — (C 2 H 3 0)' > 2 . 
(NO.)' J 

A tribasic acid is formed upon the type of a treble molecule of water, 
thus — 

Type, tt 3 > 3 , tribasic phosphoric acid, -pry// \ 3 , triphosphate of 

sodium, pQ 3 „ \ 3 , common phosphate of sodium, -p%// \ 8 , microcos- 

mic salt (phosphate of sodium and ammonium), pry// f 3 . 
But in this case also an unknowrE radical, PO, is assumed. 

TT ~i 

If pyrophosphoric acid be represented by /poy/'/po V I ^ 4 ^ s ^ er " 

TT -\ 

mediate position between metaphosphoric acid p^ , >• 0, and orthopia 

TT ") 

phoric acid pry// [ 3 is at once apparent. 



os- 



CHEMISTRY OF THE METALS. 



180. The general principles of chemistry having been explained and 
illustrated in the history of the non-metallic elements, the chemistry of 
the metals will be discussed with less attention to details, which, 
however interesting in a strictly chemical sense, are not, at present, 
of immediate practical importance. 

The definition of a metal has been already given at p. 27, as an 
element capable of forming a base by union with oxygen. 

POTASSIUM. 

K' = 39 parts by weight. 

The indispensable alkali, potash, appears to have been originally 
derived from the granitic rocks, where it exists in combination with 
silicic acid and alumina, in the well-known minerals, feldspar and mica. 
These rocks having, in course of time, disintegrated to form soils for 
the support of plants, tho potash has been converted into a soluble 
state, and has passed into the plants as a necessary portion of their 
food. 

In the plant, the potash is found to have entered into various forms 
of combination ; thus, most plants contain sulphate of potash and 
chloride of potassium ; but the greater portion of the potash exists in 
combination with certain vegetable acids formed in the plant, and 
when the latter is burnt, the salts of potash with the vegetable acids 
are decomposed by the heat, leaving the potash in combination with 
carbonic acid, forming carbonate of potash (K 2 O.C0 2 ). 

Carbonate of potash. — When the ashes of plants are treated with 
water, the salts of potash are dissolved, those of lime and magnesia 
being left. On separating the aqueous solution and evaporating it to a 
certain point, a great deal of the sulphate of potash, being much less 
soluble, is deposited, and the carbonate of potash remains in the solu- 
tion; this is evaporated to dryness, when the carbonate of potash is 
left, mixed with much chloride of potassium, and some sulphate of 
potash ; this mixture constitutes the substances imported from America 
and other countries where wood is abundant, under the name of potashes, 
which are much in demand for the manufacture of soap and glass. When 
further purified, these are sold under the name of pearlash, but this is still 
far from being pure carbonate of potash. 

During the fermentation of the grape-juice, in the preparation of wine, 
a hard crystalline substance is deposited, which is known in commerce 
by the name of argol, or when purified, as cream of tartar. The chemical 



258 CAUSTIC POTASH. 

name of this salt is bitartrate of potash, for it is derived from potash and 
tartaric acid, a vegetable acid having the composition H 2 O.C 4 H 4 5 . 
When this salt (K 2 O.H 2 0.2C 4 H 4 5 ) is heated, the tartaric acid is decom- 
posed into a variety of products, among which are found carbonic acid, 
which remains in combination with the potash, and carbon, which is left 
mixed with the carbonate of potash ; but if the heat be continued, and 
free access of air permitted, the carbon will be entirely burnt away, and 
carbonate of potash will be left {salt of tartar). 

In wine-producing countries, carbonate of potash is prepared from the 
refuse yeast which rises during the fermentation, and is dried in the sun 
in order to be subsequently incinerated. 

The fleeces of sheep contain a considerable proportion of potash com- 
bined with an animal acid ; when the fleece is washed with water, the 
salt of potash is dissolved out, and on evaporating the liquid and burning 
the residue, it is converted into carbonate of potash. 

Hydrate of potash (K 2 O.H 2 0, or KHO). — Carbonate of potash was 
formerly called potash, and was supposed to be an elementary substance. 
It was known that its alkaline qualities were rendered far more powerful 
by treating it with lime, which caused it to be termed mild alkali, in 
order to distinguish it from the caustic* alkali obtained by means of lime, 
and possessed of very powerful corrosive properties. Lime, it was said, 
is derived from limestone by the action of fire, and therefore owes its 
peculiar properties to the acquisition of a certain amount of the matter 
of fire, which, in turn, it imparts to the mild alkali, and thus confers upon 
it a caustic or burning power. 

Black's researches in the middle of the eighteenth century, which are 
often referred to as models of inductive reasoning, exposed the fallacy of 
this explanation, and proved that instead of acquiring anything from the 
fire, the limestone actually lost carbonic, acid, and instead of imparting 
anything to the mild alkali, the lime really gained as much carbonic acid 
as it had previously lost. 

The caustic potash, so largely employed by the soap-maker, is obtained 
by adding slaked lime to a boiling diluted solution of the carbonate 
of potash, when the water of the hydrate of lime is exchanged for 
the carbonic acid, and the carbonate of lime is deposited at the bottom of 
the vessel, whilst hydrate of potash remains in the clear solution — 



K 2 O.C0 2 + CaO.H 2 = 


= CaO.C0 2 + K 2 O.H 2 


Carbonate of Hydrate of 


Carbonate of Hydrate of 


potash. lime. 


lime. potash. 



If the solution of carbonate of potash be too strong, the lime will 
not remove the whole of the carbonic acid. 

When the solution is evaporated, the hydrate of potash remains as a 
clear oily liquid, which solidifies to a white mass as it cools, and forms 
the fused potash of commerce, which is often cast into cylindrical sticks 
for more convenient use.t The hydrate of potash is the most powerful 
alkaline substance in ordinary use, and is very frequently employed by 
the chemist on account of its energetic attraction for the different acids. 
It is generally used in the state of solution, the strength of which is 
inferred from its specific gravity, this being higher in proportion to the 
amount of potash contained in the solution. 

* From Kaiu), to burn. 

t These have sometimes a gi'eenish colour, due to the presence of some manganate of 
potash. 



POTASSIUM. 



259 



Potassium. — Of the composition of hydrate of potash nothing was known 
till the year 1807, when Davy succeeded in decomposing it by the gal- 
vanic battery; this experiment, which deserves particular notice, as being 
the first of a series resulting in the discovery of so many important metals, 
was made in the following manner : — a fragment of hydrate of potash, 
which, in its dry state, does not conduct electricity, was allowed to become 
slightly moist by exposure to the air, and placed upon a plate of platinum 
attached to the positive (copper) end of a very powerful galvanic battery; 
when the wire connected with the negative (zinc) end was made to touch 
the surface of the hydrate of potash, some small metallic globules resem- 
bling mercury made their appearance at the extremity of this (negative) 
wire, at which the hydrogen contained in the hydrate of potash was also 
eliminated, whilst bubbles of oxygen were separated on the surface of the 
platinum plate connected with the positive wire (see p. 5). By allow- 
ing the negative wire to dip into a little mercury contained in a cavity 
upon the surface of the potash, a combination of potassium with mercury 
was obtained, and the mercury was afterwards separated by distillation. 
This process, however, furnished the metal in very small quantities, and, 
though it was obtained with 
greater facility a year or two 
afterwards by decomposing 
hydrate of potash with 
white-hot iron, some years 
elapsed before any consider- 
able quantity of potassium 
was prepared by the present 
method of distilling in an 
iron retort an intimate 
mixture of carbonate of pot • 
ash and carbon, obtained 
by calcining cream of tar- 
tar ; in this process the 
oxygen of the potash is re- 
moved by the carbon in 
the form of carbonic oxide 
(K 2 O.C0 2 + C 2 = K 2 + 
3CO). 

The annexed figure repre- 
sents the iron retort connected 
with its copper receiver, sur- 
rounded with cold water, and containing petroleum to protect the distilled potassium 
from oxidation. The lateral tube of the receiver permits the tube of the retort to be 
cleared, if necessary, during the distillation, by the passage of an iron rod. 

Some of the most striking properties of this metal have already been 
referred to (p. 10) ; its softness, causing it to be easily cut like wax, the 
rapidity with which its silvery surface tarnishes when exposed to the air, 
its great lightness (sp. gr. 0-865), causing it to float upon water, and its 
taking fire when in contact with that liquid, sufficiently distinguish it 
from other metals. It fuses easily when heated, and is converted, at a 
higher temperature, into a green vapour ; if air be present, it burns with 
a violet-coloured flame, and is converted into anhydrous potash, the oxide 
of potassium (K 2 0). 

The property of burning with this peculiar violet-coloured flame is 




Fig. 234. — Preparation of potassium. 



260 



COMPOUNDS OF POTASSIUM. 



characteristic of potassium, and allows it to be recognised in its com- 
pounds. 

If a solution of nitrate of potash (saltpetre) in water be mixed with enough spirit 
of wine to allow of its being inflamed, the flame will have a peculiar lilac colour. 
This colour may also be developed by exposing a very minute particle of saltpetre, 
taken on the end of a heated platinum wire, to the reducing (inner) blowpipe flame 
(fig. 235), when the potassium, being reduced to the metallic state, and passing 
into the oxidising (outer) flame in the state of vapour, imparts to that flame a lilac 
tinge. 




Fig. 235. — Coloured flame test. 



The difficulty and expense attending the preparation of potassium have 
prevented its receiving any application except in purely chemical opera- 
tions, where its attraction for oxygen, chlorine, and other electronegative 
elements, is often turned to account. 

The chloride of potassium (KC1) is an important natural source of this 
metal, being extracted from sea-water, from kelp (the ash of sea-weed), and 
from the refuse of the manufacture of sugar from beet-root. It also occurs 
in combination with chloride of magnesium, forming the mineral known 
as carnallite (K 2 Cl.MgCl 2 .6H 2 0), an immense saline deposit overlying 
the rock-salt in the salt-mines of Stassfurth in Saxony. Carnallite re- 
sembles rock-salt in appearance, but is very deliquescent ; it promises to 
become the most important source of potassium hitherto discovered. 

Bicarbonate of potash (K 2 O.H 2 0.2C0 2 , or KHC0 3 ), which is much 
used in medicine, is obtained by passing carbonic acid through a strong 
solution of carbonate of potash, when it is deposited in crystals, being 
much less soluble in water than the normal carbonate. 

Nitrate of potash (Kft.Nfi 5 , or KN0 3 ), or saltpetre, will be specially 
considered in the section on gunpowder. 

The following less important compounds of potassium have not been noticed else- 
where, and are not of sufficient practical importance to require particular description 
in this work : — 



Peroxide of potassium, 


K 2 2 


Sesquisulphide of potassium, 


■K2S3 


Monosulphide , , 


K 2 S 


Tetrasulpliide , , • 


*A 


Disulphide , , 


K 8 S 2 


Pentasulphide ,, 


K 2 S, 



EXTRACTION OF COMMON SALT. 261 

SODIUM. 

Na' = 23 parts by weight. 

other mM™m is^often found, in place of potassium, in the feldspars and 
form of common saifT^MP far more abundantly supplied with it in the 
solid state, but dissolved in seV-wlium, NaCl), occurring not only in the 
waters derived from most lakes, rivers, and spnngi»aller quantity in the 

Rock-salt forms very considerable deposits in many region*, , 
country the most important is situated at Northwich in Cheshire, where very 
large quantities are extracted by mining. Wielitzka, in Poland, is cele- 
brated for an extensive salt mine, in which there are a chapel and dwell- 
ing-rooms, the furniture of which is made of this rock. Extensive beds 
of rock-salt also occur in France, Germany, Hungary, Spain, Abyssinia, 
and Mexico. Perfectly pure specimens form beautiful colourless cubes, 
and are styled sal gem ; but ordinary rock-salt is only partially trans- 
parent, and exhibits a rusty colour, due to the presence of iron. In some 
places the salt is extracted by boring a hole into the rock and filling 
it with water, which is pumped up when saturated with salt, and evapo- 
rated in boilers, the minute crystals of salt being removed as they are 
deposited. 

At Droitwich, in Worcestershire, the salt is obtained by evaporation from 
the waters of certain salt springs. In some parts of France and Germany 
the water from the salt springs contains so little salt that it would not 
pay for the fuel necessary to evaporate the water, and a very ingenious 
plan is adopted, by which the proportion of water is greatly reduced with- 
out the application of artificial heat. For this purpose a lofty scaffolding is 
erected and filled with bundles of brushwood, over which the salt water 
is allowed to flow, having been raised to the top of the scaffolding by 
pumps. In trickling over the brushwood this water exposes a large sur- 
face to the action of the wind, and a considerable evaporation takes place, 
so that a much stronger brine is collected in the reservoir beneath the 
scaffolding ; by several repetitions of the operation, the proportion of water 
is so far diminished that the rest may be economically evaporated by arti- 
ficial heat. The brine is run into boilers and rapidly boiled for about 
thirty hours, fresh brine being allowed to flow in continually, so as to 
maintain the liquid at the same level in the boiler. During this ebullition 
a considerable deposit, composed of the sulphates of lime and soda, is 
formed, and raked out by the workmen. When a film of crystals of salt 
begins to form upon the surface, the fire is lowered and the temperature of 
the brine allowed to fall to about 180° F., at which temperature it is 
maintained for several days whilst the salt is crystallising. The crystals 
are afterwards drained and dried by exposure to air. The grain of the 
salt is regulated by the temperature at which it crystallises, the size of the 
crystals increasing as the temperature falls. It is not possible to extract 
the whole of the salt in this way, since the last portions which crystallise 
will always be contaminated with other salts present in the brine, but the 
mother-liquor is not wasted, for after as much salt as possible has been 
obtained, it is made to yield sulphate of soda (Glauber's salt), sulphate of 
magnesia (Epsom salts), bromine and iodine. 

The process adopted for extracting the salt from sea-water depends 
upon the climate. In Eussia, shallow pits are dug upon the shore, in 



26 2 EXTRACTION OF COMMON SALT. 

which the sea-water is allowed to freeze, when a great portion of 'ft* 
water separates in the form of pure ice, leaving a solution of salt sutn- 

*1^^*£aS^ the sea-water i, allowed to run 
very slowly through a series of shallow pits upon the shore, whsre^Ved 
comes concentrated by spontaneous evaporation, and is g^deposited. The 
to remain for some time in reservoirs in jffihjtfmmerce as bay-salt Before 
coarse crystals thus obtained- »mey are allowed to drain for a long time, 
they are sent w^aHon, when the chloride of magnesium with which they 
j~<r contaminated deliquesces in the moisture of the air and drains off. 
The bittern, or liquor remaining after the salt has been extracted, is em- 
ployed to furnish magnesia and bromine. 

Great improvements have been made during the last few years in the economical 
extraction of the salts from sea-water. It will be remembered that 1000 parts of 
sea-water contain about 

29*0 parts of chloride of sodium, 
0'5 ,, chloride of potassium, 
3'0 ,, chloride Of magnesium, 
2'5 ,, sulphate of magnesia, 
1*5 ,, sulphate of lime, &c. 

In a warm climate, that of Marseilles, for example, the water is allowed to evapo- 
rate spontaneously until it has a specific gravity of 1*24. During this evaporation 
it deposits about four-fifths of its chloride of sodium. It is then mixed with one- 
tenth of its volume of water and artificially cooled to 0° F. (see p. 123), when it de- 
posits a quantity of sulphate of soda, resulting from the decomposition of part of the 
remaining chloride of sodium by the sulphate of magnesia. The mother-liquor is 
evaporated down till its specific gravity is 1"33, a fresh quantity of chloride of 
sodium being deposited during the evaporation. "When the liquid cools it deposits 
a double salt composed of chloride of potassium and chloride of magnesium, from 
which the latter may be extracted by washing with a very little water, leaving the 
chloride of potassium fit for the market. 

This process is instructive as illustrating the influence exerted upon the arrange- 
ment of the various acids and bases in a saline solution by the temperature to which 
the solution is exposed, the general rule being that a salt is formed which is in- 
soluble in the liquid at that particular temperature. 

The great tendency observed in ordinary table salt to become damp 
when exposed to the air, is due chiefly to the presence of small quantities 
of chloride of magnesium and chloride of calcium, for pure chloride of 
sodium has very much less disposition to attract atmospheric moisture, 
although it is very easily dissolved by water, 2f parts of this liquid being- 
able to dissolve one part (by weight) of salt. 

In the history of the useful applications of common salt, is to be found 
one of the best illustrations of the influence of chemical research upon 
the development of the resources of a country, and a capital example of a 
manufacturing process not based, as such processes usually are, upon mere 
experience, independent of any knowledge of chemical principles, but 
upon a direct and intentional application of these to the attainment of a 
particular object. 

Until the last quarter of the eighteenth century, the uses of common 
salt were limited to culinary and agricultural purposes, and to the glazing 
of the coarser kinds of earthenware, whilst a substance far more useful in 
the arts, carbonate of soda, was imported chiefly from Spain under the 
name of barilla, which was the ash obtained by burning a marine plant 
known as the salsola soda. But this ash only contained about one-fourth 



MANUFACTURE OF ALKALI. 



263 



of its weight of carbonate of soda, so that this latter substance was thus 
imported at a great expense, and the manufactures of soap and glass to 
which it is indispensable were proportionally fettered. 

During the wars of the French Revolution the price of barilla had risen 
so considerably, that it was deemed advisable by Napoleon to offer a 
premium for the discovery of a process by which the carbonate of soda 
could be manufactured at home, and to this circumstance we are indebted 
for the discovery, by Leblanc, of the process at present in use for the 
manufacture of carbonate of soda from common salt, a discovery which 
placed this substance at once among the most important raw materials 
with which a country could be furnished. 

182. Manufacture of carbonate of soda from common salt. — The salt is 
spread upon the hearth of a reverberatory furnace (fig. 236),* and mixed 




Fig. 236. — Furnace for converting common salt into sulphate of soda. 

with an equal weight of sulphuric acid, which converts it into the sul- 
phate of soda (p. 153), expelling the hydrochloric acid in the form of 
gas, which would prove highly injurious to the vegetation in the neigh- 
bourhood, and is therefore usually condensed by being brought into con- 
tact with water (see p. 154). The flame of the fire is allowed to play 
over the surface of the mixture of salt and sulphuric acid until it has 
become perfectly dry ■ in this state it is technically known as salt-cake, 
and is next mixed with about an equal weight of limestone and rather 
more than half its weight of small coal; this mixture is again heated 
upon the hearth of a reverberatory furnace, when it evolves an abun- 
dance of carbonic oxide, and yields a mixture of carbonate of soda with 
lime and sulphide of calcium; this mixture is technically known as 
black-ash. 

The change which has been effected in the sulphate of soda will be 
easily understood ; for when this salt is heated in contact with carbon 
(from the small coal) it loses its oxygen, and becomes sulphide of sodium, 
whilst carbonic acid is evolved ; thus — 



Na o 0.$0, 



Na.,S 



2CO... 



* The hearth of this furnace is usually divided, as seen in the figure, into two compart- 
ments, in one of which (lined with lead), more remote from the grate, the decomposition is 
effected, the acid being poured in through the funnel, while in that nearest to the grate, 
lined with fire-brick, the whole of the hydrochloric acid is expelled, and the sulphate of 
soda fused. 



264 RECOVERY OP SULPHUR FROM ALKALI WASTE. 

Again, when carbonate of lime is heated in contact with carbon, carbonic 
oxide is given off, and lime remains — 

CaO.C0 2 + C = 2CO + CaO . 

Finally, when sulphide of sodium and lime are heated together in the 
presence of carbonic acid, carbonate of soda and sulphide of calcium are 
produced — 

Na 2 S + CaO + C0 2 - Na 2 O.C0 2 + CaS. 

When the black ash is treated with water, the carbonate of soda is dis- 
solved, leaving the sulphide of calcium, arid by evaporating the solution, 
ordinary soda ash is obtained. But this is by no means pure carbonate 
of soda, for it contains, in addition to a considerable quantity of common 
salt and sulphate of soda, a certain amount of caustic soda or hydrate of 
soda, formed by the action of the excess of lime upon the carbonate of soda. 
Tn order to purify it, the crude soda ash is mixed with small coal or saw- 
dust and again heated, when the carbonic acid formed from the carbona- 
ceous matter converts the hydrate of soda into carbonate, and on dissolving 
the mass in water and evaporating the solution, it deposits oblique 
rhombic prisms of common washing soda, having the composition, 
Na 2 O.CO 2 .10Aq. (soda crystals). 

A little reliection will show the important influence which this process 
has exerted upon the progress of the useful arts in this country. The 
three raw materials, salt, coal, and limestone, we possess in abundance. 
The sulphuric acid, when the process was first introduced, bore a high 
price, but the resulting demand for this acid gave rise to so many im- 
provements in its manufacture that its price has been very greatly 
diminished, — a circumstance which has, of course, produced a most 
beneficial effect upon all branches of manufacture in which the acid is 
employed. 

The large quantity of hydrochloric acid obtained as a secondary pro- 
duct has been employed for the preparation of bleaching powder, and 
the important arts of bleaching and calico-printing have thence re- 
ceived a considerable impulse. These arts have also derived a more 
direct benefit from the increased supply of carbonate of soda, which 
is so largely used for cleansing all kinds of textile fabrics. The manufac- 
tures of soap and glass, which probably create the greatest demand for 
carbonate of soda, have been increased and improved beyond all prece- 
dent by the production of this salt from native sources. 

Recovery of sulphur from alkali-waste. — Since nearly the whole of the sulphur 
which is employed, in the form of sulphuric acid, for decomposing the common salt, 
is obtained at the alkali-works in the form of sulphide of calcium in the tank- 
icaste left after exhausting the black ash with water, several processes have been 
devised for recovering the sulphur in order to employ it again for the manufac- 
ture of oil of vitriol. The simplest of these consists in blowing air through the 
moist tank-waste, until it is converted into a mixture of bisulphide of calcium and 
hyposulphite of lime, the oxidation being stopped when one-third of the bisulphide 
of calcium has been converted into hyposulphite. 

(1.) 2CaS + = CaO + CaS 2 . (2.) CaS 2 + 3 = CaO.S 2 2 . 

When the yellow liquor thus obtained is decomposed by the muriatic acid from the 
alkali-works, the sulphur is precipitated ; 

Ca0.S 2 2 + 2CaS 2 + 6HC1 = S 6 + 3CaCl 2 + 3H 2 . 

An objection to this process appears to be the difficulty in procuring a sufficient 



SODA-CRYSTALS — SODA-LYE. 265 

quantity of muriatic acid, for which there is a great demand on the part of the 
producers of bleaching powder and bicarbonate of soda. 

Another process for recovering the soda employs the waste liquor from the chlorine 
stills (see p. 144), which contains chloride of manganese (MnCl 2 ) and perchloride of 
iron (Fe 2 Cl e ). On treating the sulphide of calcium in the soda- waste with this still 
liquor, chloride of calcium and sulphides of iron and manganese are produced ; 

MnCl 2 + CaS - MnS + CaCl 2 ; Fe 2 Cl 6 + 3CaS = Fe 2 S 3 + 3CaCl 2 . 

By exposing these sulphides to the air, in a moist state, the sulphur is separated, 
and the metals are converted into oxides. 

2MnS + 3 = Mn 2 3 + S 2 ; Fe 2 S 3 + 3 = Fe 2 3 + S 3 . 

By stirring these oxides with more soda-waste, the sulphides are reproduced ; 
and are afterwards again oxidised by exposure to air, so as to separate their sulphur. 
The sulphur thus separated combines with the sulphide of calcium in a fresh por- 
tion of the waste, to form a bisulphide, one-third of which is oxidised by the air, as 
in the process first described, and converted into hyposulphite of lime. In order to 
precipitate the sulphur from the liquor containing the bisulphide of calcium and 
hyposulphite of lime, the excess of hydrochloric acid always present in the chlorine 
still liquor is turned to account ; the sulphur liquor is run into this until the precipi- 
tated sulphur begins to be accompanied by a black precipitate of sulphide of iron, 
showing that all the free acid has been neutralised. The still liquor thus neutralised 
is then employed for decomposing a fresh portion of the soda-waste as at the 
commencement of the process. The precipitated sulphur is pressed to free it from 
the liquor, dried, and melted by super-heated steam. 

Although the chemistry of this process is rather elaborate, the practical working 
is said to be very simple and inexpensive. 

The crystals of carbonate of soda are easily distinguished by their pro- 
perty of efflorescing in dry air (p. 41), and by their alkaline taste, which 
is much milder than that of carbonate of potash, this being, moreover, a 
deliquescent salt. The crystals are very soluble in water, requiring only 
2 parts of cold and less than their own weight of boiling water ; the 
solution is strongly alkaline to test papers. 

The substance commonly used in medicine under the name of carbonate 
of soda, is really the bicarbonate (Na 2 O.C0 2 .H 2 O.C0 2 or NaHC0 3 ), and 
is prepared by saturating the carbonate of soda with carbonic acid gas. 
It is readily distinguished from the carbonate, as it is but slightly alkaline, 
and is very much less easily dissolved by water. 

Soda lye, employed in the manufacture of hard soap, is a solution of 
hydrate of soda (Na 2 O.H 2 or NaHO), obtained by decomposing the 
carbonate of soda with hydrate of lime (slaked lime, CaO.H 2 0), when 
the water of this latter compound is exchanged for the carbonic acid 
of the carbonate. 

The solid hydrate of soda of commerce is generally obtained in the 
process for manufacturing carbonate of soda, just described ; the solution 
obtained by treating the black ash with water is concentrated by evapo- 
ration, so that the carbonate and sulphate of soda and chloride of sodium 
may crystallise out, leaving the hydrate of soda, which is far more soluble, 
in the liquid. The latter, which still contains a compound of sulphide of 
sodium and sulphide of iron, which gives it a red colour, is mixed with 
some nitrate of soda to oxidise the sulphides, and evaporated down until a 
fused mass of hydrate of soda is left, which is poured out into iron moulds.* 

* Another plan of treating the black ash liquor consists in allowing it to trickle through 
a column of coke against a current of air, when the sulphide of sodium (Na 2 S) is oxidised 
and converted into soda (Na 2 0) and hyposulphite of soda (Na 2 S 2 3 ), whilst the sulphide of 
iron is deposited. The liquor is mixed with a little chloride of lime to oxidise any remain- 
ing sulphides, and concentrated by evaporation, when carbonate of soda and ferrocyanide 
of sodium are deposited in crystals. The liquor separated from these contains the hydrate 
of soda, and is evaporated till it solidifies on cooling. 



266 SODIUM — BORAX. 

Kryolite (SlSTaF.AlFg) is sometimes employed as a source of the sodium 
for hydrate of soda, which may be obtained by decomposing it with 
hydrate of lime. 

183. Sodium. — Potash and soda exhibit so much similarity in their 
properties, that we cannot be surprised at their having been confounded 
together by the earlier chemists, and it was not till 1736 that Du Hamel 
pointed out the difference between them. The discovery of potassium 
naturally led Davy to that of sodium, which can be obtained by processes 
exactly similar to those adopted for procuring potassium, to which it will 
be remembered sodium presents very great similarity in properties (p. 11). 
Sodium, however, is readily distinguished from potassium by its burning 
with a yellow flame, which serves even to characterise it when in 
combination. 

This yellow flame is well seen by dissolving salt in water in a plate, and adding 
enough spirit of wine to render it inflammable, the mixture being well stirred while 
burning. If a little piece of sodium be burnt in an iron spoon held in a flame, all 
the flames in the room, even at a remote distance, will be tinged yellow. The 
blowpipe flame may also be employed to detect sodium by this colour, as in the 
case of potassium (p. 260). In fireworks, nitrate of soda is employed for producing 
yellow flames. A very good yellow fire may be made by intimately mixing, in a 
mortar, 74 grs. of nitrate of soda, 20 grs. of sulphur, 6 grs. of sulphide of antimony, 
and 2 grs. of charcoal, all carefully dried, and very finely powdered. 

The preparation of sodium, by distilling a mixture of carbonate of soda 
and charcoal, is much easier than that of potassium, for which reason 
sodium is far less costly than that metal, and has received applications, on 
the large scale, during the last few years, for the extraction of the metals 
aluminum, and magnesium. An amalgam of sodium (p. 126) is also 
employed with advantage in extracting gold and silver from their ores. 
To obtain sodium in large quantity, a mixture of dried carbonate of soda, 
powdered coal, and chalk, is distilled in iron cylinders, when the oxygen 
of the soda is abstracted by the carbon, which it converts into carbonic 
oxide, and the sodium passes over in the form of vapour. 
Na 2 O.C0 2 + C 2 = !Na 2 + 3CO . 
The chalk is employed to prevent the fusion of the mixture. 

184. Borax, biborate of, soda (Na 2 0.2B 2 3 ). — A very important com- 
pound of soda is used in the arts under the name of borax, in which the 
soda is combined with boracic acid. It has already been stated that this 
substance is deposited during the evaporation of the waters of certain 
lakes in Thibet, whence it is imported into this country in impure crystals, 
which are covered with a peculiar greasy coating. The refiner of tincal 
powders the crystals and washes them, upon a strainer, with a weak 
solution of soda, which converts the greasy matter into a soap and dissolves 
it. The borax is then dissolved in water, a quantity of carbonate of soda 
is added to separate some lime which the borax usually contains, and, 
after filtering off the carbonate of lime, the solution is evaporated to the 
crystallising point and allowed to cool, in order that it may deposit the 
pure crystals of borax. 

It appears, however, that the greater part of the borax employed in the 
arts is manufactured in this country by heating carbonate of soda with 
boracic acid, when the latter expels the carbonic acid and combines with 
the soda.* The mass is then dissolved in water, and the borax crystal- 

* The ammonia which is evolved from the Tuscan boracic acid employed in this process 
is known in commerce as Volcanic ammonia, and is free from the empyreumatic odour 
which generally accompanies that from coal and bones. 



SILICATE OF SODA. 267 

lised an opera± i ^ n «pon which, much, care is bestowed, since the product 
flops 'not meet with a ready sale unless in large crystals. 

The solution of borax, having been evaporated to the requisite degree of 
concentration, is allowed to crystallise in covered wooden boxes, which 
are lined with lead and enclosed in an outer case of wood, the space 
between the sides of the case and the box being stuffed with some bad 
conductor of heat, so that the solution of borax may cool very slowly, and 
large crystals may be deposited. In about thirty hours the crystallisation 
is completed, when the liquid is drawn off as rapidly as possible, the last 
portion being carefully soaked up with sponges, so that no small crystals 
may be afterwards formed upon the surface of the large ones ; the case 
is then again covered up, so that the crystals may cool slowly without 
cracking. 

Borax is chemically known as hiborate of soda, and is represented, in 
the dry state, by the formula Na 2 0.2B 2 3 . The ordinary prismatic crys- 
tals, however, contain ten molecules of water of crystallisation, and are, 
therefore, represented by the formula 2STa 2 O.2B 2 O 3 .10Aq. They soon 
effloresce and become opaque when exposed to air, and may readily be 
distinguished by their alkaline taste and action upon test-papers, and 
especially by their behaviour when heated, for they fuse easily and intu- 
mesce most violently, swelling up to a white spongy mass of many times 
their original bulk ; this mass afterwards fuses down to a clear liquid 
which forms a transparent glassy mass on cooling (vitrified borax), and 
since this glass is capable of dissolving many metallic oxides with great 
readiness (borax being, by constitution, an acid salt, and therefore ready 
to combine with more base), it is much used in the metallurgic arts. 
Large quantities of borax are also employed in glazing stoneware. 

185. Silicate of soda. — A combination of soda with silicic acid has 
long been used, under the name of soluble glass, for imparting a fire-proof 
character to wood and other materials, and, more recently, for producing 
artificial stone for building purposes, and for a peculiar kind of permanent 
fresco-painting (stereochromy), the results of which are intended to with- 
stand exposure to the weather. 

Soluble glass is usually prepared by fusing 15 parts of sand with 8 parts 
of carbonate of soda and 1 part of charcoal. The silicic acid, combining 
with the soda, disengages the carbonic acid, the expulsion of which is 
facilitated by the presence of charcoal, which converts it into carbonic 
oxide. The mass thus formed is scarcely affected by cold water, but dis- 
solves when boiled with water, yielding a strongly alkaline liquid. 

In using this substance for rendering wood fire-proof, a rather weak 
solution is first applied to the wood, and over this a coating of lime-wash 
is laid, a second coating of soluble glass (in a more concentrated solu- 
tion) is then applied. The wood so prepared is, of course, charred, as 
usual, by the application of heat, but its inflammability is remarkably 
diminished. 

For the manufacture of Ransome's artificial stone, the soluble glass is 
prepared by heating flints, under pressure, with a strong solution of hydrate 
of soda, to a temperature between 300° and 400° F., when the silicic acid 
constituting the flint enters into combination with the soda. Finely 
divided sand is moistened with this solution, pressed into moulds, dried, 
and exposed to a high temperature, when the silicate of soda fuses and 
cements the grains of sand together into a mass of artificial sandstone, to 



268 SALTS OF AMMONIA. 

which any required colour may be imparted \>y m^i>, g metallic oxides 
with the sand before it is moulded. 

Silicate of soda is also sometimes used as a dung substitute (p. 246) in 
calico-printing. 

Sulphate of soda forms the very common saline efflorescence upon the 
surface of brick walls, and has been found covering the sandy soil of the 
Desert of Atacama, over a considerable area. The mineral known as 
Thenar dlle also consists of sulphate of soda, and Glauberite is a double 
sulphate of soda and lime (]Na 2 O.S0 3 , CaO.S0 3 ) which is nearly insoluble 
in water. 

Phosphate of soda (2Na 2 O.H 2 O.P 2 5 .24Aq.) is obtained by neutralising, 
with carbonate of soda, the impure phosphoric acid obtained by decom- 
posing bone-ash with sulphuric acid (p. 231). On evaporation, the phos- 
phate is deposited in oblique rhombic prisms which effloresce in air. 

Nitrate of soda (aSTa 2 0.!N~ 2 5 or NaN0 3 ) will be more particularly 
noticed in the section on gunpowder. It is imported from Peru, and used 
in considerable quantity as a manure, and for the manufacture of nitrate 
of potash. 

SALTS OF AMMONIA. 

186. The great chemical resemblance between some of the salts of am- 
monia and those of potash and soda has been already pointed out as afford- 
ing a reason for the hypothesis of the existence of a compound metal, 
ammonium (NH 4 ), equivalent in its functions to potassium and sodium. 
However convenient this assumption may be for the purpose of repre- 
senting by equations the chemical changes in which the salts of ammonia 
take part, it is evidently necessary to place these salts on a different 
footing from those of potash and soda, until either the metal itself or 
its oxide (NH 4 ) 2 0, which is at present equally hypothetical, shall be 
obtained. This has become the more necessary since modern chemistry 
has brought to light certain organic bases which exhibit a stronger resem- 
blance to potash and soda than that evinced by ammonia, rendering it 
necessary to extend to these also the hypothesis of the existence of com- 
pound metals, and thus to encumber chemical pages with the names of a 
large class of substances of the existence of which there is no direct 
evidence. 

Much encouragement has been afforded to the belief in the existence of 
oxide of ammonium (NH 4 ) 2 0, by the circumstance that the compounds 
which are formed when ammonia (NH 3 ) combines with the anhydrous acids', 
such as carbonic (C0 2 ) and sulphuric (S0 3 ), do not exhibit the resem- 
blance to the salts of potash and soda until water is added, the elements 
of which are required to convert (NH 3 ) 2 into (NH 4 ) 2 0. Thus, by the 
action of dry ammonia gas upon anhydrous sulphuric acid, a compound 
called sulphuric ammonide is formed, having the composition (NH 3 ) 2 .S0 3 . 
This substance dissolves in water and crystallises in octahedra, but its 
solution is not precipitated by chloride of barium, which always precipi- 
tates the true sulphates, nor by chloride of platinum, which precipitates 
the true salts of ammonia. By long boiling with water, however, it 
becomes converted into the sulphate of ammonia, 2NH 3 .H 2 O.S0 3 (or sul- 
phate of oxide of ammonium, (NH 4 ) 2 O.S0 3 , which yields precipitates with 
both the above tests. The anhydrous phosphoric, carbonic, and sulphurous 
acids also combine with dry ammonia to form ammonides, which do not 



SALTS OF AMMONIA. 269 

respond to the ordinary tests for the corresponding salts of ammonia nntil 
after water has been assimilated. The true salts of ammonia are pro- 
duced either by the combination of a hydrated acid with ammonia, or by 
double decomposition. 

187. Sulphate of ammonia (2NH 3 .H 2 O.S0 3 , or (NH 4 ) 2 S0 4 ) is largely 
employed in the preparation of ammonia-alum, and of artificial manures, 
for which purposes it is generally obtained from the ammoniacal liquor 
of the gas-works by neutralising with sulphuric acid and evaporating. 
The rough crystals are gently heated to expel tarry substances, and 
purified by recrystallisation. The crystals have the same shape as those 
of sulphate of potash, and are easily soluble in water. When heated to 
about 500° F. the sulphate of ammonia is decomposed, yielding vapour of 
sulphite of ammonia (2N"H 3 .H 2 O.SO.,), water, ammonia, nitrogen, and 
sulphurous acid. If muslin be dipped into a solution of sulphate of 
ammonia in ten parts of water, and dried, it will no longer burn with 
flame when ignited. The mineral mascagnine consists of sulphate of 
ammonia. This salt is occasionally found in needle-like crystals upon the 
windows of rooms in which coal-gas is burnt. The bisulphate of ammonia 
contains NH 3 .H 2 O.S0 3 , or NH 4 HS0 4 . 

188. Sesquicarbonate o/«mmo??ia(4NH 3 .2H 2 0.3C0 2 , or 2(NH 4 ) 2 0.3C0 2 ) 
is the common carbonate of ammonia of the shops, also called smelling 
salts or Preston salts, largely used in medicine, and by bakers and confec- 
tioners, for imparting lightness or porosity to cakes, &c. It is com- 
monly prepared by mixing sal-ammoniac (hydrochlorate of ammonia) 
with twice its weight of chalk, and distilling the mixture in an earthen 
or iron retort communicating, through an iron pipe, with a leaden chamber 
or receiver, in which the sesquicarbonate of ammonia collects as a trans- 
parent fibrous mass, which is extracted by taking the receiver to pieces, 
and purified by resubliming it at about 130° F., in iron vessels sur- 
mounted by leaden domes. The action of carbonate of lime upon hydro- 
chlorate of ammonia would be expected to furnish the neutral carbonate 
(2NH 3 .H 2 O.C0 2 ), or (NH 4 ) 2 C0 3 , but this salt (even if produced) is decom- 
posed by the heat employed in the process, with loss of ammonia and 
water, and formation of sesquicarbonate of ammonia — 

6(NH 3 .HC1) + 3(CaO.C0 2 ) = 
4]STH 3 .2H 2 0.3C0 2 + 2NH 3 + H 2 + 3CaCl 2 . 

When a mass of freshly prepared sesquicarbonate of ammonia is 
exposed to air, it evolves ammonia and carbonic acid, and becomes gradually 
converted into an opaque crumbly mass of bicarbonate of ammonia — 

4NH 3 .2H 2 0.3C0 2 = 2KH 3 + C0 2 + 2(NH 3 .H 2 O.C0 2 ). 

Water effects this decomposition more rapidly ; if the powdered sesqui- 
carbonate of ammonia be washed with a little water, bicarbonate of 
ammonia is left, and the solution contains the elements of neutral car- 
bonate of ammonia (2NH 3 .H 2 O.C0 2 ), but this salt has not been obtained 
in the solid form. The sesquicarbonate dissolves in about three times its 
weight of cold water. Boiling water decomposes it, and the solution, on 
cooling, deposits large prismatic crystals of bicarbonate of ammonia 
(NH 3 .H 2 O.C0 2 ) which is much less soluble in water. This salt has 
been found in considerable quantity, forming crystalline masses in a bed 
of guano on the western coast of Patagonia. Sal volatile is an alcoholic 
solution of carbonate of ammonia obtained by distilling sal-ammoniac 



270 SAL-AMMONIAC. 

with carbonate of potash and rectified spirit of wine, or by treating the 
sesquicarbonate of ammonia with hot spirit. 

By dissolving sesquicarbonate of ammonia in strong solution of am- 
monia, and adding alcohol, prismatic crystals of the sesquicarbonate, of 
the formula 4NH 3 .2H 2 0.3C0 2 .2Aq., may be obtained. 

189. Hydrochloride of ammonia (NH 3 .HC1), or chloride of ammonium 
(NH 4 C1), also called muriate of ammonia and sal-ammoniac. — When dry 
ammonia gas is brought in contact with an equal volume of dry hydro- 
chloric acid gas, it has been seen (p. 125) that they combine directly to 
produce the hydrochlorate of ammonia, the preparation of which on the 
large scale has been noticed at p. 1201 It is also sometimes made by 
subliming a mixture of sulphate. of ammonia with common salt — 

2NH3.lip.SO3 + 2NaCl - 2(NH 3 .HC1) + ]STa 2 O.S0 3 . 

Its commercial form is that of a very tough translucent fibrous mass, 
generally of the dome-like shape of the receivers, and often striped with 
brown, from the presence of a little iron. It has not the least smell of 
ammonia, and is very soluble in water, requiring about three parts of cold 
water, and little more than its own weight of boiling water. As the hot 
solution cools, it deposits beautiful fern-like crystallisations composed of 
minute cubes and octahedra. The liquefaction of sal-ammoniac in water 
lowers the temperature very considerably, which renders the salt very 
useful in freezing mixtures. A mixture of equal weights of sal-ammoniac 
and nitre, dissolved in its own weight of water, lowers the temperature 
of the latter from 50° F. to 10°. In this case partial decomposition takes 
place, resulting in the production of chloride of potassium and nitrate of 
ammonia, both of which absorb much heat whilst being dissolved by 
water. The solution of hydrochlorate of ammonia in water is slightly 
acid to blue litmus paper. When sal-ammoniac is heated, it passes off in 
vapour, at a temperature below redness, without previously fusing \ the 
vapour forms thick white clouds in the air, and may be recondensed as a 
white crust upon a cold surface ; but it cannot be sublimed without some 
loss, a portion being decomposed into hydrochloric acid, hydrogen, and 
nitrogen. 

The specific gravity (weight of 1 vol.) of the vapour of sal-ammoniac is 
13*3 times that of hydrogen, so that 53*5 parts, or one molecule, would 
appear to occupy 4 vols, instead of 2, but this may be explained by sup- 
posing a temporary dissociation of the hydrochloric acid and ammonia 
when the salt is converted into vapour, so that the observed specific 
gravity is really that of a mixture of equal volumes of these constituent 
gases. Some experimental evidence has been obtained in support of this 
view, for it has been found that free ammonia and hydrochloric acid may 
be separated by diffusion from the vapour obtained on heating hydro- 
chlorate of ammonia. Moreover, the heat which becomes latent or is 
absorbed in vaporising the sal-ammoniac is almost exactly that which is 
produced by the combination of the hydrochloric acid and ammonia. When 
this salt is heated with metallic oxides, its hydrochloric acid often con- 
verts the oxide into a chloride which is either fusible or volatile, so that 
sal-ammoniac is often employed for cleansing the surfaces of metals pre- 
viously to soldering them. Even those metallic oxides which are 
destitute of basic properties, such as antimonic and stannic acids, are 
convertible into chlorides by the action of sal-ammoniac at a high tem- 
perature. 



LITHIUM. 271 

Hydrochlorate of ammonia is found in volcanic districts, and is present 
in very small quantity in sea-water. 

190. Hydrosulphate of ammonia (2NEL.H 2 S), or sulphide of ammonium 
(NH 4 ) 2 S, has been obtained in colourless crystals by mixing hydrosulphuric 
acid gas with twice its volume of ammonia gas in a vessel cooled by a 
mixture of ice and salt. It is a very unstable compound, decomposing at 
the ordinary temperature of the air into free ammonia and bi-hydrosulphate 
of ammonia, NH,.H 2 S, which may be obtained in very volatile colour- 
less needles by passing equal volumes of its constituent gases into a vessel 
cooled in ice. When a solution of ammonia is saturated with hydrosul- 
phuric acid gas, the ammonia is found to have combined with two 
molecules, forming a solution of the bi-hydrosulphate or hydrosulphate of 
ammonium (NH 4 HS). The solution is colourless when freshly prepared, 
but it soon becomes yellow in contact with the air, from the formation 
of the bisulphide of ammonium (]STH 4 ) 2 S 2 ), hyposulphite of ammonia being 
formed at the same time — 

4(KE 4 HS) + 5 - (NH 4 ) 2 S 2 + (ISrH 4 ) 2 S 2 3 + 2H 2 . 

Eventually, the solution deposits sulphur and becomes colourless, hypo- 
sulphite, sulphite, and sulphate of ammonia being formed. When the 
freshly prepared colourless solution of the bi-hydrosulphate of ammonia is 
mixed with an acid, the solution remains clear, hydrosulphuric acid being 
evolved with effervescence; NH : ,H 2 S + HC1 - NH 3 .HC1 + H 2 S ; 
but if the solution be yellow, a milky precipitate of sulphur is produced, 
from the decomposition of the bisulphide of ammonium — 

(ira 4 ) 2 S 2 + 2HC1 = 2KH 4 C1 4- H 2 S + S. 

The fresh solution gives a black precipitate of sulphide of lead when 
solution of acetate of lead :.s added to it, but after it has been kept till it 
is of a dark yellow or red colour, it gives a red precipitate of the per- 
sulphide of lead. Solution of hydrosulphate of ammonia, prepared by 
mixing the bi-hydrosulphate with an equal volume of solution of ammonia, 
is largely employed in analytical chemistry. The solution has a very 
disagreeable odour. 

Bisulphide of ammonium is obtained in deliquescent yellow crystals, when a mixture 
of ammonia gas with vapour of sulphur is passed through a red-hot porcelain tube. 
It is the chief constituent of Boyle's fuming liquor, a fetid yellow liquid obtained by 
distilling sal-ammoniac with sulphur and lime. The bisulphide of ammonium is 
sometimes deposited in yellow crystals from this liquid. By dissolving sulphur in 
the bisulphide of ammonium, orange-yellow prismatic crystals of pentasulphide of 
ammonium (NH 4 ) 2 S 5 may be obtained. Even a heptasulphide of ammonium (NH 4 ) 2 S 7 
has been crystallised. 

Compounds may be obtained in which the sulphide of ammonium (NH 4 ) 2 S plays 
the part of a sulphur-base towards the sulphides of arsenic, antimony, and other 
sulphur-acids. 

It is scarcely possible to represent the constitution of the higher sulphides of 
ammonium except on the ammonium hypothesis. 

The hydrolromate of ammonia (NH 3 .HBr), or bromide of ammonium (NH 4 Br), and 
the hydriodate of ammonia (ISTHg.HI), or iodide of ammonium (NH 4 I), are useful in 
photography. They are both colourless crystalline salts, but the iodide is very liable 
to become yellow or brown, from the separation of iodine, unless kept dry and in 
the dark. Both salts are extremely soluble in water. 

191. Lithium (L = 7 parts by weight) is a comparatively rare metal, obtained chiefly 
from the minerals lepidolite {\zvrU, a scale) or lithia-mica, containing silicate of 
alumina with fluorides of potassium and lithium ; petalite (wireckov, a leaf), silicate of 
soda, lithia, and alumina, and triphane or spodumene {vvoVof, ashes), which has a 



272 



SPECTKUM ANALYSIS. 



similar composition. Its name (from \&os, a stone) was bestowed in the belief that it 
existed only in the mineral kingdom, but recent investigation has detected it in 
minute proportion in the ashes of tobacco and other plants. 

Metallic lithium is obtained by decomposing fused chloride of lithium by a gal- 
vanic current. It is remarkable as the lightest of the solid elements (sp. gr. 0*59). 
It bears a general resemblance to potassium and sodium, but is harder and less 
easily oxidised than those metals. It decomposes water rapidly at the ordinary 
temperature, but does not inflame upon it. 

The alkali lithia (L 2 0) powerfully corrodes platinum when heated upon it, and also 
differs from potash and soda by forming a sparingly soluble phosphate (3L 2 O.P 2 5 ) 
and carbonate (L 2 O.C0 2 ). The compounds of lithium impart a red colour to the 
flame of the blowpipe (p. 260). 

Carbonate of lithia is occasionally employed medicinally. 

Rubidium (Rb' = 85 parts by weight) and Cesium (Cs'=133 parts by weight) 
were discovered so lately as in 1860, by Bunsen and Kirchhoff, during the analysis 
of a certain spring water which contained these metals in so minute quantity (2 or 3 
grs. in a ton) that they would certainly have escaped observation if the analysis had 
been conducted in the ordinary way. The discovery of these metals, as well as of 
two others (thallium and indium) to be mentioned hereafter, was the result of the 
application of the method of spectrum analysis, of which a brief description is here 
given, although the discussion of the optical principles upon which it depends would 
be misplaced in a chemical work. 

192. Spectrum analysis. — It has been mentioned above that compounds 
of potassium, sodium, and lithium impart, respectively, lilac, yellow, and 
red colours to the blowpipe flame (or air-gas flame, see p. 103), or, in 
other words, that the highly heated vapours of the metals evolve luminous 
rays of these particular colours. When the quantity of the metal is 
extremely minute, and its peculiar luminous rays proportionally scanty, 
their colour may very easily escape notice, especially if two or three metals 
are present in the flame at the same time. But if the light emanating 
from the flame be collected by a lens (at A, fig. 237), and transmitted 
through a prism of flint glass, or through a hollow prism filled with 

bisulphide of carbon (B), all 
the rays of one colour will 
be refracted in a definite 
direction, so that the spec- 
trum, or image of the flame, 
when thrown upon a screen, 
instead of exhibiting colours 
uniformly distributed like 
the flame itself, will show 
stripes or bands of the vari- 
ous coloured rays existing in 
the flame. Thus, when va- 
pour of sodium is present in 
the flame, the whole of the 
yellow light emitted by it will be collected in the spectrum into a narrow 
yellow stripe of great intensity, and so extremely delicate is this test that 
it is scarcely possible to obtain a flame which does not exhibit this sodium 
line. The heated vapour of lithium emits a mixture of red with a few 
yellow rays, and accordingly, the spectrum of a flame containing lithium 
exhibits a very bright band of red light, and a comparatively dull band 
of yellow light, the red band being characteristic of lithium. The potas- 
sium flame emits a mixture of blue and red rays, so that its spectrum 
exhibits a distinct red band of a darker colour than the lithium band, and 
a feeble violet band. Instead of throwing the spectrum upon a screen, it 




Fig. 237.— Spectroscope. 



RUBIDIUM — CjESIUM. 



273 



is generally passed through a telescope (C) to the eye of the observer, 
and the spectroscope so constructed has now taken its place among the 
apparatus indispensable to the analytical chemist. The prism B may be 
slowly moved round by a handle attached to a stage on which it rests, 
in order that the different parts of the spectrum may be successively 
brought into sight. By comparing the spectra of the flames containing 
vapours of the metals with a picture or map of the solar spectrum (fig. 
238), the exact position of the various coloured bands may be noted, and 
thus, if several metals are present in the same flame, they may still be dis- 
tinguished by the colours and positions of their bands. Thus, if a mixture 
of the chlorides of potassium, sodium, and lithium be taken upon a loop 
of platinum wire and held in the flame, the dull red line of potassium 
(K, fig. 238) is seen close to one end of the spectrum, at some distance 
from it the bright red band (L) of lithium ; at about the same distance 



Violet. Indigo. JBlue 



Green. 



Yellow. Oranc/e. Red. 




Spectrum furnished by solar light decomposed by a pri 









B ""* 
V5 U 



g 6 



Six 



K. 



Coloured bands in the spectrum. 
Fig. 238. 
from this, the pale yellow lithium line ; and close to this, the bright yel- 
low band of sodium (N&) ; whilst near to the other end of the spectrum 
is the feeble violet band of potassium (k). The chlorides of the metals 
are most suitable for this experiment, on account of their easy conversion 
into vapour. 

When examining, with the spectroscope, the alkaline chlorides extracted from the 
spring water above alluded to, Bunsen and Kirchhoff observed two red and two blue 
bands in the spectrum, which they could not ascribe to any known substance, and 
which they ultimately traced to the two new metals, rubidium {rubidus, dark-red) 
and caesium (ccesius, sky-blue). 

Rubidium has since been found in small quantity in other mineral waters, in 
lepidolite and in the ashes of many plants. This metal is closely related in pro- 
perties to potassium, but is more easily fusible and convertible into vapour, and 
actually surpasses that metal in its attraction for oxygen, rubidium taking fire 
spontaneously in air. It burns on water with exactly the same flame as potassium. 
Its oxide, rubidia (Eb 2 0), is a powerful alkali, like potash, and its salts are isomor- 
phous with those of potash. The double chloride of platinum and potassium, how- 
ever, is eight times as soluble in boiling water as the corresponding salt of rubidium, 
which is taken advantage of in separating these two allied metals. 

Caesium appears to be even more highly electropositive than rubidium, forming a 

s 



274 BARIUM. 

strong alkali, ccesia (Cs 2 0), with oxygen, and salts which are isomorphous with those 
of potassium. Carbonate of csesia, however, is soluble in alcohol, which does not 
dissolve the carbonates of potash and rubidia. Moreover, the bitartrate of csesia is 
nine times as soluble in water as the bitartrate of rubidia. 

Csesium has been found in lepidolite ; and the rare mineral pollux found in Elba, 
and resembling feldspar in composition, is said to contain a very large quantity of 
this metal. 

193. General review of the group of alkali-metals. — Caesium, rubidium, 
potassium, sodium, and lithium, constitute a group of elements conspicuous 
for their highly electropositive character, trie powerfully alkaline nature of 
their oxides, and the general solubility of their salts. Their chemical 
characters and functions are directly opposite to those of the electronegative 
group containing fluorine, chlorine, bromine, and iodine, and, like those 
elements, they exhibit a gradation of properties. Thus, caesium appears to 
be the most highly electropositive member, rubidium the next, then 
potassium and sodium, whilst lithium is the least electropositive ; and just 
as iodine, the least electronegative of the halogens, possesses the highest 
atomic number, so caesium, the least electronegative (or most electro- 
positive) of the alkali-metals, has a higher atomic weight than any other 
member of this group, their atomic weights being represented by the 
numbers, caesium, 133; rubidium, 85*3; potassium, 39; sodium, 23; 
lithium, 7. As in the case of the halogens, also, there is no reason to 
believe that the atomic weights of this group differ from their equivalent 
weights, so that they are all univalent elements. Just as chlorine is 
accepted as the representative of chlorous radicals, so potassium is com- 
monly regarded as the type of basylous radicals, the term radical being 
applied to all substances, whether elementary or compound, which are 
capable of being transferred, like chlorine or potassium, from one com- 
pound to another without suffering decomposition. 

Some of the physical properties of these elements exhibit a gradation in 
the same order as their atomic weights; thus rubidium fuses at 101° F., 
potassium at 144 0, 5, sodium at 207°*7, and lithium at 356°, so that, at 
ordinary temperatures, rubidium is the softest, and lithium the hardest of 
these metals. 

In some of their salts a similar gradational relation is observed ; the 
carbonates, for example, of caesia, rubidia, and potassa, are highly deli- 
quescent, absorbing water greedily from the air, whilst carbonate of soda 
is not deliquescent, and carbonate of lithia is sparingly soluble in water. 
The difficult solubility of the carbonate and phosphate of lithia consti- 
tutes the connecting link between this and the succeeding group of metals, 
the carbonates and phosphates of which are insoluble in water. 

BAEIUM. 

Ba" = 1 37 parts by weight. 

194. Barium, so named from the great weight of its compounds (/Sapvs, 
heavy) is found in considerable abundance in the north of England, in two 
minerals known as Wither He (carbonate of baryta, BaO.C0 2 ) and heavy 
spar (sulphate of baryta, BaO.S0 3 ). Witherite is found in large masses 
in the lead mines at Alston Moor, and at Anglesarkin Lancashire. It is 
said to be used for poisoning rats, and was originally mistaken, on account 
of its great weight, for an ore of lead. 

The metal itself is obtained by decomposing fused chloride of barium 
by the galvanic current. It is a pale yellow, fusible, malleable metal of 



NITRATE AND HYDEATE OF BAEYTA. 275 

sp. gr. about 4, which, is easily oxidised by air, and rapidly decomposes 
water at common temperatures. 

Such compounds of baryta as are used in the arts are chiefly prepared 
from heavy spar or sulphate of baryta, which is remarkable for its insolu- 
bility in water and acids. In order to prepare other compounds of baryta 
from this refractory mineral, it is ground to powder and strongly heated 
in contact with charcoal or some other carbonaceous substance, which 
removes the oxygen from the mineral in the form of carbonic oxide, and 
converts it into sulphide of barium; BaO.S0 3 + C 4 = 4CO + BaS. 
This latter compound, being soluble in water, can be readily converted 
into other barytic compounds. 

The artificial sulphate of baryta which is used by painters, instead of 
white lead, under the name of permanent white, and is employed for 
glazing cards, is prepared by mixing the solution of sulphide of barium 
with dilute sulphuric acid, when the sulphate of baryta separates as a 
white precipitate, which is collected, washed, and dried — 

BaS + H 2 (XS0 3 = H 2 S + BaO.S0 3 . 

The artificial carbonate of baryta, which is used in the manufacture of 
some kinds of glass, is prepared by passing carbonic acid gas through a 
solution of sulphide of barium, when the carbonate of baryta is precipi- 
tated ; BaS + H 2 + C0 2 - H 2 S + BaO.C0 2 . 

In preparing compounds of barium from heavy spar on the small scale, it is better 
to convert the sulphate of baryta into carbonate of baryta. 50 grs. of the finely 
powdered sulphate are mixed with 100 grs. of dried carbonate of soda, 600 grs. of 
powdered nitre, and 100 grs. of very finely powdered charcoal. The mixture is 
placed in a heap upon a brick or iron plate, and kindled with a match, when the 
heat evolved by the combustion of the charcoal in the oxygen of the nitre, fuses the 
sulphate of baryta with the carbonate of soda, when they are decomposed into car- 
bonate of baryta and sulphate if soda — 

BaO.S0 3 + Na^O.CO, = Na 2 O.S0 3 + BaO.C0 2 . 

The fused mass is thrown into boiling water, which dissolves the sulphate of soda 
and leaves the carbonate of baryta. The latter may be allowed to settle, and washed 
several times, by decantation, with distilled water, until the washings no longer 
yield a precipitate with chloride of barium, showing that the whole of the sulphate of 
soda has been washed away, and pure carbonate of baryta remains. 

Nitrate of baryta, BaO.N 2 5 or Ba(N0 3 ) 2 , is obtained by dissolving car- 
bonate of baryta in diluted nitric acid, and evaporating the solution, when 
octahedral crystals of the nitrate are deposited. It is an ingredient in 
some kinds of blasting powder used by miners. If nitrate of baryta be 
heated in a porcelain crucible, it fuses and is decomposed, leaving a grey 
porous mass of baryta ; BaO.K" 2 5 = BaO + 2£T0 2 + O. 

Hydrate of baryta may be procured by adding 4 oz. of the powdered 
nitrate of baryta to 12 oz. of a boiling solution of hydrate of soda, of 
sp. gr. 1*13 (prepared by dissolving 3 oz. of commercial hydrate of soda in 
20 measured ounces of water) ; the solution becomes turbid from the sepa- 
ration of carbonate of baryta produced from the carbonate of soda in the 
hydrate ; it is boiling for some minutes and then filtered ; on partial 
cooling, some crystals of undecomposed nitrate of baryta are deposited, 
and if the clear liquid be poured off into another vessel and stirred, it 
deposits abundant crystals of hydrate of baryta, having the composition 
BaO.H 2 0.8Aq. ; these effloresce and become opaque when exposed to 
air, becoming BaO.H 2 O.Aq. :•• when heated to redness, they become pure 
hydrate of baryta, BaO.H 2 0, which fuses but is not decomposed when 



276 STRONTIUM. 

further heated. The hydrate of baryta is moderately soluble in water, the 
solution being strongly alkaline, and absorbing carbonic acid from the 
air, depositing carbonate of baryta. 

When baryta is heated in a tube through which oxygen or air is passed, 
it absorbs the oxygen and is converted into binoxide of barium (Ba0 9 ), 
which is employed for the preparation of peroxide of hydrogen (seep. 51). 

Chloride of barium, which is the barium compound most commonly 
employed in the laboratory, may be obtained by dissolving the carbonate 
of baryta in diluted hydrochloric acid, and evaporating the solution ; on 
cooling, the chloride is deposited in tabular crystals, BaCl 2 .2Aq. 

On the large scale it is generally manufactured by fusing heavy spar 
(sulphate of baryta) with chloride of calcium (the residue from the pre- 
paration of ammonia, see p. 120), in a reverberatory furnace — 

BaO.SO + CaCl 2 = CaO.S0 3 + BaCl 2 . 

The mass is rapidly extracted with hot water, which leaves the sulphate 
of lime undissolved, and the clear solution of chloride of barium is de- 
canted and evaporated. If the sulphate of lime and chloride of barium 
were allowed to remain long together in contact with the water, sulphate 
of baryta and chloride of calcium would be reproduced. 

Chlorate of baryta. (BaO.Cl 2 5 , or Ba (C10 3 ) 2 ) is employed in the 
manufacture of fireworks, being prepared for that purpose by dissolving 
the artificial carbonate of baryta in solution of chloric acid; it forms 
beautiful shining tabular crystals. When mixed with combustible sub- 
stances, such as charcoal and sulphur, it imparts a brilliant green colour 
to the flame of the burning mixture (see p. 164). 

All the soluble salts of barium are very poisonous. 

STRONTIUM. 

Sr" = 87 '5 parts by weight. 

195. Strontium is less abundant than barium, and occurs in nature in 
similar forms of combination. Strontianite, the carbonate of strontia 
(SrO.COj, was first discovered in the lead mines of Strontian in Argyle- 
shire, and has since been found in small quantity in some mineral waters. 

Celestine (so called from the blue tint of many specimens) is the sul- 
phate of strontia (SrO.S0 3 ), and is found in beautiful crystals associated 
with the native sulphur in Sicily. It is also met with in this country, 
and is the source from which the nitrate of strontia employed in firework 
compositions is derived. The sulphate of strontia resembles that of 
baryta with respect to its insolubility, and is converted into the soluble 
sulphide of strontium (SrS) by calcination with carbonaceous matter. 
The solution of sulphide of strontium so obtained is decomposed by nitric 
acid, and the nitrate of strontia crystallised from the solution. This salt 
forms prismatic crystals which have the formula SrO.N 2 5 .5Aq. It has 
the property of imparting a magnificent crimson colour to flames, and is 
hence largely used for the preparation of red theatrical fire. (See p. 164.) 
The other compounds of strontium possess too little practical importance, 
and too nearly resemble those of barium, to require particular description 
here. No peroxide of strontium, however, has been obtained. 

The metal itself is prepared in a similar manner to metallic barium, 
which it much resembles, though it is lighter (sp. gr. 2-54) and less 
fusible. It burns, when heated in air, with a crimson flame. 



CARBONATE OF LIME. — LIME. 277 



CALCIUM. 

Ca" = 40 parts by weight. 

196. No other metal is so largely employed in a state of combination 
as calcium, for its oxide, lime (CaO), occupies among bases much the 
same position as that which sulphuric acid holds among the acids, and is 
used, directly or indirectly, in most of the arts and manufactures. 

Like barium and strontium, it is found, though far more abundantly 
than these, in the mineral kingdom, in the forms of carbonate and sul- 
phate, but it also occurs in large quantity as fluoride of calcium (p. 181), 
and less frequently in the form of phosphate of lime (p. 223). Calcium, 
moreover, is found in all animals and vegetables, and its presence in their 
food, in one form or other, is an essential condition of their existence. 

Metallic calcium may be obtained by decomposing fused iodide of cal- 
cium with metallic sodium. It has a light golden-yellow colour, is harder 
than lead, and very malleable ; it oxidises slowly in air at the ordinary 
temperature, but when heated to redness, it fuses and burns with a very 
brilliant white light, being converted into lime (calx). It decomposes 
water at the ordinary temperature. It is lighter than barium and stron- 
tium, its specific gravity being L58. 

Carbonate op Lime (CaO.C0 2 or CaC0 3 ), from which all the manu- 
factured compounds of lime are derived, constitutes the different varieties 
of limestone which are met with in such abundance. 

Limestones and chalk are simply carbonate of lime in an amorphous or 
uncrystallised state. The oolite limestone, of which the Bath and Port- 
land building-stones are composed, is so called from its resemblance to the 
roe of a fish (<ooi/, an egg. Marble, in its different varieties, is an assem- 
blage of minute crystalline grains of carbonate of lime, sometimes varie- 
gated by the presence of oxides of iron and manganese, or of bituminous 
matter. This last constituent gives the colour to black marble. Car- 
bonate of lime is also found in large transparent rhombohedral crystals, 
which are known to mineralogists as calcareous spar, cede spar, or Iceland 
spar. When the crystals have the form of a six-sided prism, the mineral 
is termed Arragonite. The attention of the crystallographer has long 
been directed to these two crystalline forms of carbonate of lime, on 
account of the circumstance, that if a prism of arragonite be heated, it 
breaks up into a number of minute rhombohedra of calc spar. 

Carbonate of lime is a chief constituent of the shells of fishes and of 
egg shells, so that, except phosphate of lime, no mineral compound has 
so large a share in the composition of animal frames. Corals also con- 
sist chiefly of carbonate of lime derived from the skeletons of innumer- 
able minute insects. The mineral gaylussite is a double carbonate of 
lime and soda (CaO.C0 2 , Na. 2 O.C0 2 .5Aq.), and is scarcely affected by 
water unless previously heated, when water dissolves out the carbonate of 
soda. Baryto-calcite is a double carbonate of baryta and lime (BaO.CO,, 
CaO.C0 2 ). 

Lime (CaO). — The process by which lime is obtained from the car- 
bonate has been already alluded to under the name of lime-burning. In 
order that the carbonic acid may be completely expelled from the car- 
bonate of lime, it is necessary that the products of combustion of the fuel 
should be allowed to pass over the limestone, since although a very 
intense heat is insufficient to decompose carbonate of lime when shut up 
in a crucible, the decomposition is easily effected if the carbonate be 



278 



SULPHATE OF LIME. 



heated in a current of atmospheric air or of any other gas, especially if 
aqueous vapour be present, as is the case in the products oC combustion 
of the fuel. 

Accordingly, a kiln is commonly employed of the form of an inverted 
cone of brickwork (fig. 239), and into this the limestone and fuel are 
thrown in alternate layers. The former losing its carbonic acid before 
it reaches the bottom of the furnace, is raked out in the form of burnt 
or quick lime (CaO), whilst its place is supplied by a fresh layer of lime- 
stone thrown in at the top of the kiln. Fig. 240 represents another form 




€2^ 




Fis. 239.— Lime. 



Fig. 240.— Lime-kiln. 



of kiln, in which the limestone is supported upon an arch built with 
large lumps of the stone above the fire, which is kept burning for about 
three days and nights, until the whole of the limestone is decomposed. 

The usual test of the quality of the lime thus obtained consists in 
sprinkling it with water, with which it should eagerly combine, evolving 
much heat, swelling greatly, and crumbling to a light white powder of 
hydrate of lime {slaked lime). Lime which behaves in this manner is 
termed fat lime ; whereas, if it be found to slake feebly, it is pronounced 
a poor lime, and is known to contain considerable quantities of foreign 
substances, such as silica, alumina, magnesia, &c. Lime is said to be 
overburnt when it contains hard cinder-like masses of silicate of lime, 
formed by the combination of the silica, which is generally found in lime- 
stone, with a portion of the lime, under the influence of excessive heat in 
the kiln. 

The hydrate of lime is about twice as soluble in cold as it is in hot 
water, so that lime-water should always be made by shaking slaked linie 
with cold distilled water, which dissolves about l-700th of its weight ; 
the solution is allowed to settle in a closed bottle, for it absorbs carbonic 
acid rapidly from the air. Crystals of hydrate of lime have been obtained 
by evaporating lime-water in vacuo. 

Sulphate of Lime in combination with water (CaO.S0 3 .H 2 O.Aq.) is 
met with in nature, both in the form of transparent prisms of selenite, 
and in opaque and semi-opaque masses known as alabaster and gypsum. 
It is this latter form which yields plaster of Paris, for when heated to 
between 300° and 400° F., it loses its water, and if the mass be then 
powdered, and again mixed with water, the powder reeombines with it 



MAGNES1AN MINERALS. 279 

to form a mass of hydrated sulphate of lime, the hardness of which nearly 
equals that of the original gypsum. 

In the preparation of plaster of Paris, a number of large lumps of 
gypsum are built up into a series of arches, upon which the rest of the 
gypsum is supported ; under these arches the fuel is burnt, and its flame 
is allowed to traverse the gypsum, care being taken that the temperature 
does not rise too high, or the gypsum is overburnt and does not exhibit 
the property of recombining with water. When the operation is supposed 
to be completed, the lumps are carefully sorted, and those which appear 
to have been properly calcined are ground to a very fine powder. When 
this powder is mixed with water to a cream, and poured into a mould, the 
minute particles of anhydrous sulphate of lime (CaO.S0 3 ) combine with 
2 molecules of water to reproduce the original gypsum (CaO.S0 3 .H 2 O.Aq.), 
and this act of combination is attended with a slight expansion which 
forces the plaster into the finest lines of the mould. 

Stucco consists of plaster of Paris (occasionally coloured) mixed with a 
solution of size ; certain cements used for building purposes (Keene's and 
Keating's cements) are prepared from burnt gypsum, which has been 
soaked in a solution of alum and again burnt ; and although the plaster 
thus obtained takes much longer to set than the ordinary kind, it is much 
harder, and therefore takes a good polish. 

Plaster of Paris is much damaged by long exposure to moist air, from 
which it regains a portion of its water, and its property of setting is so far 
diminished. 

Precipitated sulphate of lime is used by paper-makers under the name 
of pearl hardener. 

Chloride of calcium (CaCl 2 ) has been mentioned as the residue left in 
the preparation of ammonia. The pure salt may be obtained by dissolving 
pure carbonate of lime (white marble) in hydrochloric acid, and evaporat- 
ing the solution, when prismatic crystals of the composition CaCl 2 .6Aq. 
are obtained. When these are heated they melt, and at about 390° F. 
are converted into a white porous mass of CaCl 2 .2Aq., which is much 
used for drying gases. At a higher temperature, fused chloride of calcium, 
free from water, is left ; this is very useful for removing water from some 
liquids. A saturated solution of chloride of calcium boils at 355° P., and 
is sometimes used as a convenient bath for obtaining a temperature above 
the boiling point of water. 

When hydrate of lime is boiled with a strong solution of chloride of 
calcium, it is dissolved, and the filtered solution deposits prismatic crystals 
of oxy chloride of calcium, CaCl 2 .3Ca0.15Aq., which are decomposed by 
pure water. 



MAGNESIUM. 

Mg"=24 - 3 parts by weight. 

197. Magnesium is found, like calcium, though less abundantly, in 
each of the three natural kingdoms. Among minerals containing this 
metal, those with which we are most familiar are certain combinations of 
silica and magnesia (silicates of magnesia) known by the names of talc, 
steatite or French chalk, asbestos, and meerschaum, which always contains 
water. Magnesite is a carbonate of magnesia. Most of the minerals 
containing magnesium have a remarkably soapy feel. The compounds of 



280 SULPHATE OF MAGNESIA. 

magnesium, which are employed in medicine, are derived either from the 
mineral dolomite or magnesian limestone, which contains the carbonate 
of magnesia and carbonate of lime, or from the sulphate of magnesia, 
which is obtained from sea-water and from the waters of many mineral 
springs. 

Metallic magnesium has acquired some importance during the last few 
years as a source of light. When the extremity of a wire of this metal 
is heated in a flame, it takes fire, and burns with a dazzling white light, 
becoming converted into magnesia (MgO). If the burning wire be plunged 
into a bottle of oxygen, the combustion is still more brilliant. The light 
emitted by burning magnesium is capable of inducing chemical changes 
similar to those caused by sun-light, a circumstance turned to advantage 
for the production of photographic pictures by night. Attempts have 
been made to introduce magnesium as an illuminating agent for general 
purposes, but the large quantity of solid magnesia produced in its com- 
bustion forms a very serious obstacle to its use. The metal is extracted 
from the chloride of magnesium (see p. 1 15) by fusing it with sodium, using 
chloride of sodium and fluoride of calcium to promote the fusibility of the 
mass. 

On a small scale, magnesium may be prepared by mixing 900 grs. of chloride of 
magnesium with 150 grs. of fluoride of calcium, 150 of fused chloride of sodium, 
and 150 of sodium cut into slices (see p. 115). The mixture is thrown into a 
red-hot earthen crucible, which is then covered and again heated. When the 
action appears to have terminated, the fused mass is stirred with an iron rod to 
promote the union of the globules of magnesium. It is then poured upon 
an iron tray, allowed to solidify, broken up, and the globules of magnesium 
separated from the slag ; they may be collected into one globule by throwing 
them into a melted mixture of chlorides of magnesium and sodium and fluoride of 
calcium. 

In most of its physical and chemical characters magnesium resembles 
zinc, though its colour more nearly approaches that of silver ; in ductility 
and malleability it also surpasses zinc. It is nearly as light, however, 
as calcium, its specific gravity being 1'74. It fuses below a red heat, 
and may be distilled like zinc. Cold water has scarcely any action 
upon magnesium ; even when boiled it oxidises the metal very slowly. 
In the presence of acids, however, it is rapidly oxidised by water. 
Solution of hydrochlorate of ammonia also dissolves it, owing to the 
tendency of the magnesium salts to form double salts with those of 
ammonia — 

4(NH 3 .HC1) + Mg -- 2(NH 3 .HCl).MgCl a + H 2 + 2NH 3 . 

Magnesium is one of the few elements which unite directly with nitrogen 
at a high temperature. The nitride of magnesium, N 2 Mg 3 , has been 
obtained in transparent crystals, and is evidently composed after the type 
2NH,, so that it is not surprising that the action of water upon it gives 
rise to magnesia and ammonia, N 2 Mg 3 + 6HO = 2NH 3 + 3MgO. 

The sulphate of magnesia, so well known as Epsom salts, is sometimes 
prepared by calcining dolomite to expel the carbonic acid, washing the 
residual mixture of lime and magnesia with water to remove part of the 
lime, and. treating it with sulphuric acid which converts the lime and 
magnesia into sulphates; and since the sulphate of lime is almost in- 
soluble in water, it is readily separated from the sulphate of magnesia 
which passes into the solution, and is obtained by evaporation in pris- 
matic crystals having the composition MgO.S0 3 .H 2 0.6Aq. The prepara- 






. COMPOUNDS OF MAGNESIA. 281 

tion of Epsom salts from sea-water has already been alluded to (p. 262). 
In some parts of Spain, sulphate of magnesia is found in large quantities 
(like nitre in hot climates) as an efflorescence upon the surface of the 
soil. This sulphate of magnesia, as well as that contained in w T ell-waters, 
appears to have been produced by the action of sulphate of lime, originally 
present in the water, upon magnesian limestone rocks; MgO.C0 2 + 
CaO.S0 3 = MgO.SO ? + CaO.C0 2 . 

The water of constitution in the sulphate of magnesia may be displaced 
by the sulphate of an alkali without alteration in its crystalline form ; 
a double sulphate of magnesia and potash (MgO.S0 3 , K 2 O.S0 3 .6Aq.), 
and a similar salt of ammonia (MgO.S0 3 , 2NH 3 .H 2 O.S0 3 .6Aq.) maybe thus 
obtained. The mineral poly halite (iroAvs, many, aks, salt) is a remarkable 
salt, containing MgO.S0 3 , K 2 O.S0 3 , 2(CaO.S0 3 ), 2H 2 0.* Water decom- 
poses it into its constituent salts. 

The preparation commonly used in medicine under the name of mag- 
nesia, is really a basic carbonate of magnesia, or a compound of carbonate 
of magnesia with hydrate of magnesia and water in the proportions 
expressed by the formula, 3(MgO.C0 2 ).MgO.H 2 0.3Aq. It is obtained 
by mixing boiling solutions of sulphate of magnesia and carbonate of soda, 
when one-fourth of the carbonic acid is expelled in the state of gas ; the 
white precipitate is thrown upon a cloth strainer, well washed, and dried 
in rectangular moulds. 

Another process for preparing carbonate of magnesia consists in heating 
magnesian limestone to low redness, so as to decompose the carbonate of 
magnesia which it contains, and exposing it, under pressure, to the action 
of water and carbonic acid, which dissolves the magnesia and leaves the 
carbonate of lime. On boiling the solution, to expel the excess of car- 
bonic acid, the carbonate of magnesia is precipitated. 

By moderately heating the carbonate of magnesia, its water and carbonic 
acid are expelled, and pure or calcined magnesia (MgO) is left, which is 
very slightly soluble in water and feebly alkaline. 

The mineral periclase consists of magnesia in a crystallised form. Mag- 
nesia combines with water to form a hydrate (MgO.H 2 0), but not with 
evolution of heat, as in the cases of baryta, strontia, and lime. Crys- 
tallised hydrate of magnesia constitutes the mineral brucite. Magnesia, 
like lime, is remarkable for its infusibility. 

It has recently been noticed that calcined magnesia, when mixed with 
water, solidifies after a time into a very hard compact mass of hydrate of 
magnesia (MgO.H 3 0), and may serve, like plaster of Paris, for taking 
casts. Dolomite calcined below redness also sets to a very hard mass with 
water. 

The phosphate of magnesia (3MgO.P 2 5 ) enters into the composition of 
bones, and the, phosphate of magnesia and ammonia (2MgO. 2]STH 3 . H 2 O.P 2 5 ), 
or triple 'phosphate, is found in calculi and in the minerals guanite and 
struvite. 

Borate of magnesia composes the mineral boracite; hydroboracite is a 
hydrated borate of lime and magnesia. 

Serpentine and olivine are silicates of magnesia and protoxide of iron. 
Some of the varieties of serpentine are employed for preparing the com- 
pounds of magnesia, for they are easily decomposed by acids with separa- 
tion of silica. 

Pearl-spar is a crystallised carbonate of lime and magnesia. 
* Polyhalite and kieserite MgO.S0 3 , H 2 are found in the salt-beds of Stassfurth . 



282 REVIEW OF THE ALKALINE EARTH METALS. 

Chloride of magnesium is important as the source of metallic mag- 
nesium. It is easily obtained in solution by neutralising hydrochloric 
acid with magnesia or its carbonate, but if this solution be evaporated in 
order to obtain the dry chloride, a considerable quantity of the salt is 
decomposed by the water at the close of the evaporation, leaving much 
magnesia mixed with the chloride (MgCl 2 + H 2 = 2HC1 + MgO). This 
decomposition may be prevented by mixing the solution with three parts 
of hydrochlorate of ammonia for every part of magnesia, when a double 
salt MgCl 2 .NH 3 .HCl is formed, which may be evaporated to dryness 
without decomposition, and leaves fused chloride of magnesium when 
further heated, the hydrochlorate of ammonia being volatilised. The 
chloride of magnesium absorbs moisture very rapidly from the air, and is 
very soluble in water. Like all the soluble salts of magnesium, it has a 
decidedly bitter taste. When magnesia is moistened with a strong solu- 
tion of chloride of magnesium, it sets into a hard mass like plaster of Paris, 
apparently from the formation of an oxy chloride MgO.MgCl 2 . It may 
be mixed with several times its weight of sand, and will bind it firmly 
tjgether. 

198. General review of the metals of the alkaline earths. — Barium, 
strontium, calcium, and magnesium form a highly interesting natural 
group of metals related to each other in a most remarkable manner. 
They exhibit a marked gradation in their attraction for- oxygen; barium 
is more readily tarnished or oxidised, even in dry air, than strontium, and 
strontium more readily than calcium; whilst magnesium is not at all 
affected by dry air, and is comparatively slowly tarnished even in moist 
air. Again, the three first metals decompose water at the ordinary tempera- 
ture, combining with its oxygen and liberating the hydrogen, but mag- 
nesium requires the aid of heat to effect this decomposition. The oxides 
of the metals exhibit a similar gradation ' in properties ; baryta, strontia, 
and lime combine with water very energetically with great evolution of 
heat, whilst in the case of magnesia no rise of temperature is observed ; 
the hydrate of baryta does not lose its water, however strongly it may be 
heated, whereas the hydrates of strontia and lime are decomposed at a red 
heat, and hydrate of magnesia even at a lower temperature. Then hydrate 
of baryta and hydrate of strontia are far more soluble in water than hydrate 
of lime (which requires about 700 parts of water to dissolve it), and all 
these three exhibit a very decided alkaline reaction which entitles them 
to the name of alkaline earths; but hydrate of magnesia requires about 
3000 parts of water to dissolve it, and is so feebly alkaline, that it ' 
might even be fairly classed among the earths proper. 

Among the other compounds of these metals, the sulphates may be 
named as presenting a gradation of a similar description; for sulphate 
of baryta may be said to be insoluble in water, sulphate of strontia dis- 
solves to a very slight extent, sulphate of lime is rather more soluble, and 
the sulphate of magnesia is very readily dissolved by water. It will be 
seen hereafter that the sulphates of the earths proper are remarkable for 
their solubility in water, so that, in this respect also, magnesia appears 
to stand on the border line between the two classes. 

The manner in which these metals are associated in nature is also not 
without its significance; for if two of them are found in the same 
mineral, they will usually be those which stand next to each other in 
the group ; thus carbonate of strontia is found together with carbonate 



ATOMIC HEATS. 283 

of baryta in witherite, whilst carbonate of lime is associated with the 
sulphate of strontia in celestine. Again, carbonate of strontiais often 
found with carbonate of lime in arragonite, and the carbonate of mag- 
nesia occurs with carbonate of lime in dolomite. 

199. Equivalent and atomic weights of barium, strontium, calcium, 
and magnesium. — The analysis of chloride of barium has proved it to 
contain 68*5 parts by weight of barium, combined with 1 eq. (35*5 
parts) of chlorine; whence the equivalent of barium is accepted as 
68 "5. In a similar manner, that of strontium has been fixed at 43' 8, 
that of calcium at 20, and that of magnesium at 12; so that here, as 
in the group of alkali-metals, the equivalent numbers decrease with the 
diminution of the electropositive character in the metals. 

Relation between sjjecific heats and equivalent weights. Atomic heats. — 
Since the specific volumes of the vapours of these metals have not been 
ascertained, recourse is had to their specific heats in order to ascertain 
their atomic weights. It will be remembered that the specific heat of 
a substance is the quantity of heat required to raise it 1° in tempera- 
ture, as compared with the quantity of heat required to raise an equal 
weight of water 1°; or, more concisely, the quantity of heat required 
to raise one part by weight of the substance 1° (referred to water as the 
unit). 

Thus, the specific heats of potassium, sodium, and lithium are, respec- 
tively, 0*1696, 0*2934, and 0*9408; these numbers representing the 
relative quantities of heat required to raise one part by weight of each 
of these metals 1° in temperature, supposing that an equal weight of 
water would be raised 1° by a quantity of heat expressed by one. ^Nb 
simple relation can be traced between these numbers, but if the quan- 
tities of heat be calculated which are required to raise equivalent weights 
of these elements 1°, the case will be different. 

If 0*1696 be the quantity of heat required to raise one part by weight 
of potassium 1°; 0*1696 x 39, or 6*61, will represent the quantity of heat 
required to raise 39 parts (1 eq.) of potassium 1°. In the same way, 
0*2934 x 23, or 6*75, is the quantity of heat required to raise 23 parts 
(1 eq.) of sodium 1°; and 0*9408 x 7, or 6*59, is the quantity required 
to raise 7 parts (1 eq.) of lithium 1°. Allowing for experimental error in 
the determination of the specific heats, these numbers, 6*61, 6*75, and 
6*59, may be regarded as representing the same quantities of heat. Since 
the atomic weights of potassium, sodium, and lithium are expressed by 
the same numbers as their equivalent weights (see p. 274), the numbers, 
6*61, 6*75, and 6*59, would represent the atomic heats of these metals, 
that is, the relative quantities of heat required to raise an atom of each 1° 
in temperature. 

The atomic heat, therefore, which is common to these three metals, may 
be represented by the mean of the three numbers, or 6*65. 

The experiments which have been made to determine the specific heats 
of those elements which can be obtained in a similar physical condition, 
lend strong support to the belief that the atomic heats of all elements 
belonging to the same group are identical, and even hold out a prospect 
of the identity of the atomic heats of a great majority of the elementary 
bodies. 

A similar relation has been observed between the atomic heats of com- 
pound bodies belonging to the same group ; thus, if the specific heats of 



284 ALUMINUM. 

the chlorides of potassium, sodium, and lithium be multiplied by the 
atomic weights of those chlorides, the product in each case will approach 
very nearly to the number 12*69. If these chlorides be allowed to con- 
tain one atom of each of their constituents, and it be supposed that the 
atomic heats of these constituents are identical, the half of this number 
(or 6*34) should represent the atomic heat of the alkali-metals, and, in 
fact, it does nearly coincide with that number (6*65). 

The specific heats of barium, strontium, and calcium have not been 
determined, and therefore their atomic heats cannot be directly ascertained. 
The specific heat of magnesium, however, is 0*2499, and if the atomic 
weight of this metal were identical with its equivalent (12), its atomic 
heat would be represented by the number 3 ; but if the atomic weight be 
regarded as double the equivalent, or 24, the atomic heat will be 
(0*2499 x 24) 6, a number more nearly approaching to the atomic heats 
of the alkali-metals. This is one reason for supposing that the atomic 
weight of magnesium is realty represented by 24. 

The specific heats of the chlorides of barium, strontium, calcium, and 
magnesium have been ascertained to be represented by the numbers 
0-0900, 0-1180, 0*1686, and 0-1970, respectively. Now, if the atomic 
weights of these metals be regarded as identical with their equivalent 
weights, the atomic heats of the chlorides, obtained by multiplying their 
atomic weights into their specific heats, would be expressed by the mean 
number 9 -36, and if this be divided by 2 (the presumed number of atoms 
in each chloride), it would give 4*68 for the atomic heat of each of the 
elements of the compound, a number which exhibits no simple relation 
to the atomic heat of magnesium, or to those of the alkali-metals. If it 
be supposed, however, that the atom of barium, strontium, calcium, or 
magnesium really represents two equivalents, so that each chloride con- 
tains three elementary atoms (two of chlorine and one of metal), the 
atomic weight of each of the chlorides would be doubled, and, conse- 
quently, the atomic heat would be twice that given above, or 18*72. 
Dividing this by 3, the presumed number of atoms in the chloride, we 
obtain the number 6 -24 for the atomic heat of each of the elements, 
which agrees very well with that directly obtained for magnesium and 
the alkali-metals. 

The metals barium, strontium, calcium, and magnesium, therefore, are 
generally regarded as bi-equivalent or diatomic elements, one atom of 
each occupying the place of two atoms of hydrogen. 



ALUMINUM. 

Al"' =27*5 parts by weight. 

200. Aluminum is the representative of the class of metals usually 
styled metals of the earths proper, and including also glucinum, thorinum, 
yttrium, zirconium, erbium, terbium, cerium, lanthanium, and didymium, 
but of these, aluminum is the only metal having any claim to our attention 
on the ground of its practical importance. 

Aluminum is distinguished among metals, as silicon is among non- 
metallic bodies, for its immense abundance in the solid mineral portion 
of the earth, to which, indeed, it is almost entirely confined, for it is 
present in vegetables and animals in so small quantity that it can scarcely 
be regarded as forming one of their necessary components. 



COMPOSITION OF CLAY. 



285 



One of the oldest rocks, which appear to have originally formed the 
basis of the solid structure of the globe, is that known as granite. This 
mineral, which derives its name from its conspicuous granular structure, 
is a mixture, in variable proportions, of quartz, feldspar, and mica, tinged 
of various colours by the presence of small quantities of the oxides of 
iron and manganese. 

Quartz, which forms the translucent or transparent grains in the granite, 
consists simply of silicic acid ; feldspar, the dull cream-coloured opaque 
part, is a combination of that acid with alumina and potash, and is 
generally spoken of as a double silicate of alumina and potash, its com- 
position being represented by the formula K 2 0.3Si0 2 ,Al 2 3 .3Si0 2 . 

Mica, so named from the glittering scales which it forms in the granite, 
is also a double silicate of alumina and potash, but the alumina is very 
frequently displaced by sesquioxide of iron, and the potash by magnesia. 

By the long- continued action of air and water, the granite rock is 
gradually crumbled down or disintegrated, an effect which must be 
ascribed to a concurrence of mechanical and chemical causes. Mechani- 
cally, the rock is continually worn down by variations of temperature, 
by the congelation of water within its minute pores, the rock being 
gradually split by the expansion attendant upon such congelation. 
Chemically, the action of water containing carbonic acid would tend to 
remove the potash from the feldspar and mica in the form of carbonate of 
potash, whilst the silicate of alumina and the quartz would subsequently 
be separated by the action of water ; the former, being so much lighter, 
would be soon washed away from the heavy quartz, and, when again 
deposited, would constitute clay. 

Although clay, therefore, always consists mainly of silicate of alumina, 
it generally contains some uncombined silicic acid, together with variable 
quantities of lime, of oxide of iron, &c. , which give rise to the numerous 
varieties of clay. 



Composition of Clay. 





Chinese Kaolin. 


Fire-clay. 
(Stourbridge). 


Pipe-clay. 


Silica 

Alumina 

"Water 

Oxide of iron .... 

Lime 

Magnesia 

Potash ) 

Soda j 


50-5 
33-7 

ii -a 

1-8 

0-8 
1-9 


64-1 

23-1 

10-0 

1*8 

0-9 


537 

32-0 

12-1 

1-4 

0-4 




99-9 


99-9 


99-6 



The silicate of alumina also constitutes the chief portion of several 
other very important mineral substances, among which may be mentioned 
slate, fuller's earth, and pumice-stone. Marl is clay containing a consider- 
able quantity of carbonate of lime. Loam is also an impure variety of 
clay. The different varieties of ochre, as well as umber and sienna, are 
simply clays coloured by the oxides of iron and manganese. 



286 MANUFACTURE OF ALUM. 

Alum, which is the chief compound of aluminum employed in the arts, 
is always obtained either from clay or slate, but there are several processes 
by which it may be manufactured. 

The simplest process is that in which pipe-clay, or some other clay con- 
taining very little iron, is calcined, ground to powder, and heated on the 
hearth of a reverberatory furnace with half its weight of sulphuric acid, 
until it becomes a stiff paste, which is then exposed to air for several 
weeks. During this time the alumina of the clay enters into combination 
with the sulphuric acid to form sulphate of alumina, which may be ob- 
tained by washing the mass with water, when the sulphate of alumina 
dissolves, and the undissolved silicic acid (still retaining a portion of the 
alumina) is left. When the solution containing the sulphate of alumina 
is evaporated to a syrupy consistence and allowed to cool, it solidifies into 
a white crystalline mass, which is used by dyers under the erroneous 
name of concentrated alum, on cake-alum, and contains about 47*5 per cent, 
of the dry salt. The sulphate of alumina can be obtained in crys- 
tals containing Al 2 3 .3S0 3 .18Aq., but there is considerable difficulty in 
obtaining these crystals on account of the extreme solubility of the salt. 
It is on account of this circumstance that the sulphate of alumina is 
usually converted into alum, which admits of very easy crystallisation 
and purification. In order to transform the sulphate of alumina into 
alum, its solution is mixed with sulphate of potash, when, by suitable 
evaporation, beautiful octahedral crystals are obtained, having the compo- 
sition Al 2 3 .3S0 3 ,K 2 O.S0 3 .24Aq. 

Alum is more commonly prepared from the mineral termed alum-shale, 
which contains silicate of alumina, together with a considerable quantity 
of finely divided iron pyrites and some bituminous matter. This shale 
is coarsely broken up, and built into long pyramidal heaps, together with 
alternate layers of coal, unless the shale, should happen to contain a suffi- 
cient amount of bitumen. These heaps are set fire to in several places, 
and are partly smothered with spent ore in order to prevent too great a 
rise of temperature. During this slow roasting of the heap, the iron 
pyrites (FeS 2 ) loses half its sulphur, which is converted by burning into 
sulphurous acid (S0 2 ), and this, in contact with the porous shale and the 
atmospheric oxygen, becomes converted into sulphuric acid (p. 202). 
This latter acid combines with the alumina to produce sulphate of alumina. 
The roasted heap is then allowed to remain for some months exposed to 
the air, and moistened from time to time, in order to promote the absorp- 
tion of oxygen by the sulphide of iron (FeS), and its conversion into sul- 
phate of iron (FeO.S0 3 ). The heap is afterwards lixiviated with water, 
which dissolves out the sulphates of alumina and iron, together with some 
sulphate of magnesia, which has also been formed in the process. When 
this crude alum liquor is evaporated to a certain extent, a large quantity 
of sulphate of iron (green vitriol) crystallises out, and the liquid from 
which these crystals have separated is then mixed with so much solu- 
tion of chloride of potassium as a preliminary experiment has shown to 
be necessary to yield the largest amount of alum. Tli£ chloride of potas- 
sium is obtained as soap-boiler's waste, and as the refuse from saltpetre 
refineries and glass-houses. The sulphate of iron still left in the solu- 
tion is decomposed by the chloride of potassium, yielding chloride of 
iron and sulphate of potash, which combines with the sulphate of alumina 
to form alum. If there be much sulphate of magnesia in the liquor, it is 
subsequently obtained in crystals and sent into the market. 



ALUMINA. 287 

Where sulphate of ammonia can be obtained at a cheap rate (as in the 
neighbourhood of the gas-works), it is very commonly substituted for the 
chloride of potassium, when ammonia-alum is obtained instead of potash- 
alum. The former is similar in all respects to the latter salt, except that 
it contains the hypothetical metal ammonium (NH 4 ) in place of potassium, 
and its formula is, therefore, A1 2 3 .3S0 3 , (NH 4 ) 2 O.S0 3 .24Aq. 

For all the uses of alum, in dyeing and calico-printing, in paper-making 
and in the manufacture of colours, ammonia-alum answers quite as well 
as potash-alum, and hence both these salts are sold under the common 
name of alum. 

These alums are the representatives of an important class of double 
sulphates, composed of a sulphate of one of the alkalies combined with 
the normal sulphate of a sesquioxide. They all contain 24 molecules of 
water of crystallisation, and their crystalline form is that of the cube or 
octahedron. 

When a solution of alum is mixed with a little solution of carbonate of 
soda, a precipitate of alumina is formed, which redissolves when the solu- 
tion is stirred. If the addition of carbonate of soda be continued as long 
as the precipitate redissolves when stirred, the salt A1 2 3 .S0 3 will remain 
in the solution — 

Al.O3.3SO3, K 2 O.S0 3 + 2(Na 2 O.C0 2 ) - A1 2 3 .S0 3 + 
2(Na 2 O.S0 3 ) + K 2 O.S0 3 + 2C0 2 . 

This solution of basic alum, as it is called, is decomposed by boiling, 
alumina being deposited and ordinary alum remaining in solution — 

3(Al 2 O s .S0 3 ) + K 2 O.S0 3 = 2A1 2 3 + A1 2 3 .3S0 3 , K 2 O.S0 3 . 

When stuffs are immersed in the solution of basic alum they also with- 
draw a portion of alumina, which becomes fixed in their fibre, and serves 
as a mordant to attract and fix the colouring matter when the stuff is 
transferred to a dye-bath. 

Alumina. — When ammonia-alum is strongly heated, it loses the whole 
of its water, ammonia,* and sulphuric acid, leaving merely a white in- 
soluble earthy substance which is alumina itself (A1 2 3 ), and differs 
widely from the metallic oxides which have been hitherto considered, by 
the feebly basic character which it exhibits. .Not only is alumina des- 
titute of alkaline properties, but it is not even capable of entirely neu- 
tralising the acids, and hence both sulphate of alumina and alum are 
exceedingly acid salts. 

Pure crystallised alumina is found in nature as the mineral corundum, 
distinguished by its extreme hardness, in which it ranks next to the 
diamond. An opaque and impure variety of corundum constitutes the 
very useful substance emery. The ruby and sapphire^ consist of nearly 
pure alumina; spinelle is a compound of magnesia with alumina, 
MgO.Al 2 3 ; whilst in the topaz the alumina is associated with silica 
and fluoride of aluminum. The mineral diaspore is a hydrate of alumina 

* The great absorption and disappearance of heat during the evaporation of the water 
and ammonia from this alum, has led to its employment for filling the space between the 
double walls of fire-proof safes, which may become red-hot outside, whilst the inside is 
kept below the scorching-point of paper. 

t Small crystals of alumina resembling natural sapphire have been obtained by the 
action of vapour of fluoride of aluminum upon boracic acid at a high temperature. By 
adding a little fluoride of chromium, crystals similar to rubies and emeralds have been 
produced. 



288 EXTRACTION OF ALUMTNUM FROM BAUXITE. 

(A1 2 8 .2H 2 0), so named from its falling to powder when heated (hiacnropa, 
dispersion). 

The artificially prepared hydrate of alumina is characterised by its gelatinous ap- 
pearance. If a little alum be dissolved in warm water, and some ammonia added 
to the solution, the ammonia will combine with the sulphuric acid, whilst the 
alumina will unite with water to form a semi-transparent gelatinous mass of hydrate 
of alumina (A1 2 3 .3H 2 0). When washed and dried, it shrinks very much and 
forms a mass resembling gum. The hydrate of alumina has a great attraction for 
most colouring matters, with which it forms insoluble compounds called lakes. 
Thus, if a solution of alum be mixed with infusion of logwood, and a little ammonia 
added, the hydrate of alumina will form, with the colouring matter, a purplish-red 
lake, which may be filtered off, leaving the solution colourless. This property is 
turned to advantage in calico-printing, where the compounds of alumina are largely 
used as mordants. 

Chloride of aluminum. — If the alumina obtained by calcining ammonia- 
alum be intimately mixed with charcoal, and strongly heated in an earthen 
tube or retort through which a stream of w 7 ell-dried chlorine is passed, 
the oxygen of the alumina is abstracted by the charcoal, to form carbonic 
oxide, whilst the chlorine combines with the aluminum yielding chloride 
of aluminum (A1 2 C1 6 ) which passes off in vapour and may be condensed, 
in an appropriate receiver, as a white crystalline solid — 

A1 2 3 + Cy + Cl 6 - A1 2 C1 6 + 3CO . 

This formation of the chloride of aluminum is possessed of some in- 
terest, as an example of the decomposition of a compound body by the 
co-operation of two elements, neither of which alone would be able to 
decompose the compound ; neither carbon nor chlorine would, alone, 
decompose alumina, however high the temperature, but when the attraction 
of the carbon for the oxygen is added to that of the chlorine for the alumi- 
num, the decomposition is easily effected. 

An impure solution of chloride of aluminum is sold as a disinfectant 
under the name of chloralum. 

But this chloride of aluminum also deserves attention as being the source 
from which the metal aluminum may be prepared in large quantities. 

201. Aluminum. — In order to obtain this interesting metal, it is only 
necessary to pass the chloride of aluminum in the state of vapour over 
heated sodium, which removes the chlorine in the form of chloride of 
sodium, leaving the aluminum as a white malleable metal about as hard 
as zinc, and fusing at a somewhat lower temperature than silver. For 
the extraction of aluminum upon the large scale, the alumina is not pre- 
pared from alum, but from the mineral known as Bauxite, which con- 
tains alumina, together with peroxide of iron and silica.* This mineral 
is heated with soda-ash (see p. 264), wdien carbonic acid escapes, and the 
silica and alumina combine with soda to form silicate of soda, and a 
soluble compound of alumina with soda, which is generally called alumi- 
nate of soda, and has the composition 3Na 2 0. A1 2 3 . On treating the mass 
with water, an insoluble silicate of alumina and soda is left, whilst the 
aluminate of soda is dissolved, and is obtained as an infusible mass when 
the solution is evaporated. This aluminate of soda is largely used by 
calico-printers as a mordant. To obtain alumina from it, the solution is 
neutralised with hydrochloric acid, which converts the sodium into 
chloride, and precipitates the alumina as hydrate of alumina (A1 2 3 . 3H 2 0). 

* This mineral is found at Baux, near Aries, in the south of France, and contains silica 
13 to 17 per cent., alumina 60 to 65, peroxide of iron 4 to 8, water 15 to 17. ■ 



MINERALS CONTAINING ALUMINA AND SILICA. 289 

As the next step towards the preparation of aluminum, the hydrate of 
alumina is mixed with charcoal and common salt, made up into balls, 
dried, and strongly heated in earthen cylinders through which dry chlorine 
is passed. The carbon abstracts the oxygen from the alumina, forming 
carbonic oxide, whilst the aluminum combines with the chlorine, and the 
chloride of aluminum so formed combines with the chloride of sodium, 
and distils over as the double chloride of aluminum and sodium 
(Al 2 Cl 6 .2NaCl). This salt is then mixed with a proper proportion of 
metallic sodium, and heated in a reverberatory furnace, when the sodium 
combines with the chlorine of the chloride of aluminum, leaving the latter 
metal to separate in a fused state beneath the melted chloride of sodium, 
which protects it from oxidation. The aluminum may be rolled into 
sheets or drawn into wire. Commercial aluminum has been found to 
contain from 3 to 7 '5 per cent, of iron. Silicon is also present in it, as 
much as 14 per cent, having been found in one sample. 

Aluminum is much more sonorous than most other metals. A bar of 
it suspended from a string, and struck with a hammer, emits a clear 
musical sound. It is remarkable as being the lightest metal capable of 
resisting the action of air even in the presence of moisture. Its specific 
gravity is 2 -5. This lightness renders it valuable for the manufacture of 
small weights, such as the grain and its fractions, since these, when made 
of aluminum, are more than three times as large as when made of brass, 
and nearly nine times as large as platinum weights of the same denomina- 
tion. It is also employed for ornamental purposes, for though not so 
brilliant as silver, it is not blackened by sulphuretted hydrogen, which so 
easily affects that metal (p. 196). 

Another characteristic feature of aluminum is its comparative resistance 
to the action of nitric acid even at a boiling heat. No other metal com- 
monly met with, except platinum and gold, is capable of resisting the 
action of nitric acid to the same extent. Hydrochloric acid, however, 
which will not attack gold and platinum, dissolves aluminum with faci- 
lity, converting it into chloride of aluminum, with disengagement of 
hydrogen; Al 2 + 6HC1 = A1 2 C1 6 + H rt . Solutions of potash and soda 
also easily dissolve it, forming the so-called aluminates of those alkalies ; 
thus 3(Na 2 O.H 2 0) + Al 2 = 3IS T a 2 O.Al 2 3 + H 6 .- Even when very strongly 
heated in air, aluminum is oxidised to a very slight extent, probably 
because the coating of alumina which is formed remains infusible and 
protects the metal beneath it. For a similar reason, apparently, aluminum 
decomposes steam slowly, even at a high temperature. 

When aluminum is fused with nine times its weight of copper, it forms 
an alloy very similar to gold in appearance, but almost as strong as iron. 
This alloy was strongly recommended to replace gold for ornamental pur- 
poses, but it does not retain its brilliancy so completely as that metal. 
Aluminum does not unite with mercury or with melted, lead, both of which 
are capable of dissolving nearly all other metals. 

202. Mineral silicates of alumina. — Many of the chemical formulae of 
minerals, which contain silicates of alumina associated with the silicates 
of other metallic oxides, are complicated, from the circumstance that a part 
of the aluminum is often replaced by iron, which, in the form of sesqui- 
. oxide (Fe 2 3 ), is isomorphous with it, and therefore capable of replacing 
it without altering the crystalline . form and general character of the 
mineral. In a similar manner, the other metals present in the mineral 

T 



290 NATURAL AND ARTIFICIAL ULTRAMARINE. 

may be exchanged for isomorphous representatives ; thus there are two 
well-known feldspars, potash -feldspar (orthoclase) and soda -feldspar 
(albite), having the formulae K 2 O.Al 2 3 .6Si0 2 , and :Na 2 O.Al 2 3 .6Si0 2 . 
These minerals are sometimes miugled in one and the same crystal 
(potash-albite or pericline) without bearing any definite equivalent pro- 
portion to each other ; the formula of such a mineral would be written 
(KNa) 2 O.Al 2 3 6Si0 2 . 

Porphyry has the same chemical composition as feldspar. 

Mica, again, is composed essentially of magnesia, alumina, and silica 
(4MgO.Al 2 ;r 4Si0 2 ), but part of the magnesium is so constantly re- 
placed by potassium and iron (as protoxide), and part of the aluminum 
by iron (as sesquioxide), that the general formula for mica must be written 
4(K 2 MgFe)0.(AlFe) 2 3 .4Si0 2 . 

Garnet is essentially a double silicate of alumina and lime, but often 
contains magnesium, iron, or manganese, replacing part of the calcium, 
and iron replacing part of the aluminum, being written — 

3(CaMgFeMn)0.(ALFe) 2 3 .3Si0 2 . 

This mineral is sometimes formed artificially in the slag of the iron blast- 
furnaces. 

Chlorite, a very important variety of rock, is a double silicate of alumina 
and magnesia, with variations as expressed by the formula — 

4(MgFe)0.(AlFe) 2 3 .2Si0 2 .3H 2 . 

Basalt is a feldspathic rock containing crystals of augite— 

4(CaMgFe)0.5Si0 2 . 

Gneiss is chemically composed like granite, but the mica is arranged in 
regular layers. Trap rock contains feldspar, together with hornblende 
which consists of silicates of alumina, lime, magnesia, and oxide of iron. 
Hornblende is sometimes found replacing the mica in granite, forming the 
rock called syenite. 

Lapis lazuli, the valuable mineral which furnishes the natural ultra- 
marine used in painting, consists chiefly of silica and alumina, which con- 
stitute respectively 45 and 32 per cent, of it, but there are also present 
9 per cent, of soda, 6 per cent, of sulphuric acid, about 1 per cent, of sul- 
phur, and a somewhat smaller quantity of iron, together with a variable 
proportion of lime. The cause of its blue colour is not understood, since 
neither of its predominant constituents is concerned in the production of 
such a colour in other cases. In consequence of the rarity of the mineral, 
the natural ultramarine bears a very high price, but the artificial ultramarine 
is manufactured in very large quantities at a low cost, and forms a very 
good imitation. One of the processes for preparing it consists in heating 
to bright redness in a covered crucible, for three or four hours, an inti- 
mate mixture of 100 parts of pure white clay (kaolin), 100 of dried car- 
bonate of soda, 60 of sulphur, and 12 of charcoal. This would be expected 
to yield a mixture of silicate of soda, aluminate of soda, and sulphide of 
sodium, the two first being white, and the latter yellow or brown, but the 
mass is found to have a green colour (green ultramarine). It is finely 
powdered, washed with water, dried, mixed with a fifth of its weight of 
sulphur, and gently roasted in a thin layer till the sulphur has burnt off, 
this operation being repeated, with fresh additions of sulphur, until the 



GLUCINUM. 291 

residue lias a fine blue colour. In the opinion of some chemists, the pre- 
sence of a small proportion of iron is essential to the blue colour, while 
others believe the colour to be due to sulphide of sodium or hyposulphite 
of soda, or both. Ultramarine is a very permanent colour under ordinary 
conditions of exposure to air and light, but acids bleach it at once, with 
separation of gelatinous silica and evolution of sulphuretted hydrogen. 
Blue writing paper is often coloured with ultramarine, so that its colour 
is discharged by acids falling upon it in the laboratory. Chlorine 
also bleaches ultramarine. Starch is often coloured blue with this sub- 
stance. 

Phosphate of alumina is found naturally in several forms. It occurs 
in large quantities in the West India Islands. Turquoise is a hydrated 
phosphate of alumina (A1 2 3 .P 2 5 ), owing its colour to the presence of 
oxide of copper.* Wavellite has the composition 3A1 2 3 .2P 2 5 . None 
of the earlier analysts detected the phosphoric acid in this mineral, on ac- 
count of the difficulty in separating it from the alumina, so that even 
in comparatively modern chemical works, it is described as a hydrate of 
alumina. 

Glucinum. 
Gl" = 9-5 parts by weight. 

203. This comparatively rare metal (which derives its name from the sweet taste of 
its salts, yxvKv;, svxet) is found associated with silica and alumina in the emerald, 
which is a double silicate of alumina and glucina, A1 2 3 . 3Si0 2 , 3(G10.Si0 2 ), and 
appears to owe its colour to the presence of a minute quantity of oxide of chromium. 
The more common mineral beryl has a similar composition, but is of a paler green 
colour, apparently caused by protoxide of iron. Chry sober yl consists of glucina and 
alumina, also coloured by iron . The earlier analysts of these minerals mistook the 
glucina for alumina, which it resembles in forming a gelatinous precipitate on add- 
ing ammonia to its solutions, but it is a stronger base than alumina, and is there- 
fore capable of displacing ammonia from its salts, and of being dissolved by them. 
Carbonate of ammonia is employed to separate the glucina from alumina, since it dis- 
solves the glucina in the cold, forming a double carbonate of glucina and ammonia, 
from which the carbonate of glucina is precipitated on boiling. Glucina (GIO) is 
intermediate in properties between alumina and magnesia, resembling the latter in 
its tendency to absorb carbonic acid from the air, and to form soluble double salts 
with the salts of ammonia, and so much resembling alumina in the gelatinous form 
of its hydrate, its solubility in alkalies, and the sweet astringent taste of its salts, 
that it was formerly regarded as a sesquioxide like alumina. 

The metal itself is very similar to aluminum. 

204. Thorinum is present in a rare Norwegian mineral, thorite, where it is asso- 
ciated with silica, lime, magnesia, and other metallic oxides. The metal itself is 
similar to aluminum, but its oxide thorina appears to be a protoxide (ThO), and 
differs from alumina and glucina in being insoluble in the alkalies (potash, for 
example), though it dissolves in carbonate of potash. Moreover, the sulphate of 
thorina is sparingly soluble in hot water, so that it is precipitated on boiling its 
solution. 

205. Yttrium and erbium are very rare metals found in gadolinite, a mineral 
silicate occurring at Ytterby in Sweden, and containing beside these, glucinum, 
cerium, and iron. Their oxides yttria (YO) and erbia, resemble thorina in being 
insoluble in the alkalies, but soluble in their carbonates ; yttria is white, but erbia 
has a yellow colour. The salts of yttria and erbia are colourless. 

206. Cerium is also found in gadolinite, but more abundantly in cerite, which is 
essentially a silicate of cerium. Phosphate of cerium (cryptolite) has also been found 
in brown apatite. This metal has been employed medicinally, in the form of oxalate 

* False or bone turquoise is fossil ivory, owing its colour to the presence of the natural 
blue phosphate of iron. 



.292 zinc. 

of cerium (CeO.C 2 3 .3H. 2 0. It forms two basic oxides, CeO, which is white, and 
forms colourless salts, and Ce 2 3 , which is yellow, and gives yellow or red salts. In 
this respect, cerium more nearly resembles iron than aluminum. These oxides of 
cerium are insoluble in the alkalies ; the protoxide is easily precipitated from its salts 
by oxalic acid in the form of the oxalate mentioned above. Sesquioxide of cerium 
does not appear to form a corresponding chloride, but yields protochloride of cerium 
and free chlorine when heated with hydrochloric acid. 

Lanthanium (from Xtx.i6a.vu, to escape notice) is also found in cerite, but it differs 
from cerium in forming only one oxide, which is white in the hydrated, but buff in 
the anhydrous state. When a mixture of nitrates of cerium and lanthanium is cal- 
cined, sesquioxide of cerium and oxide of lanthanium are left, and may be separated 
by treatment with nitric acid, diluted with 100 parts of water, which dissolves only 
the latter. 

Didymium {SfivfAos, tvdn) is very similar to lanthanium, which is associatedVith it 
in cerite. It also forms but one oxide, which is violet when hydrated, and brown 
when anhydrous. It is insoluble in potash. The salts of didymium are either pink 
or violet. 

207. Zirconium exists in the rare minerals zircon and hyacinth, in which its oxide 
zirconia (Zr0 2 ) is combined with silicic acid. Zirconia is somewhat similar to 
alumina, but is insoluble in potash, and dissolves in carbonate of potash. Its sul- 
phate, moreover, is decomposed by boiling with sulphate of potash, which removes 
part of the sulphuric acid, forming bisulphate of potash, and precipitates basic 
sulphate of zirconia. Metallic zirconium somewhat resembles amorphous silicon, 
but it decomposes water slowly at the boiling point, and has not been fused. 

ZINC. 

Zn" = 65 parts by weight. 

208. Zinc occupies a high position among useful metals, being peculiarly 
fitted, on account of its lightness, for the construction of gutters, water- 
pipes, and roofs of buildings, and possessing for these purposes a great 
advantage over lead, since the specific gravity of the latter metal is about 
1 1 *5, whilst that of zinc is only 6 -9. For such applications as these, where 
great strength is not required, zinc is preferable to iron, on account of its 
superior malleability ; for although a bar of zinc breaks under the ham- 
mer at the ordinary temperature, it becomes so malleable at 250° F as to 
admit of being rolled into thin sheets. This malleability of zinc when 
heated was discovered only in the commencement of this century, until 
which time the only use of the metal was in the manufacture of brass. 
When zinc is heated to 400° F., it again becomes brittle. The easy 
fusibility of zinc also gives it a great advantage over iron, as rendering it 
easy to be cast into any desired form; indeed, zinc is surpassed in 
fusibility (among the metals in ordinary use) only by tin and lead, its 
melting point being below a red heat, and usually estimated at 770° F. 
Zinc is also less liable than iron to corrosion under the influence of moist 
air, for although a bright surface of zinc soon tarnishes when exposed to 
the air, it merely becomes covered with a thin film of oxide of zinc (pass- 
ing gradually into basic carbonate, by absorption of carbonic acid from the 
air) which protects the metal from further action. 

The great strength of iron has been ingeniously combined with the 
durability of zinc, in the so-called galvanised iron, which is made by coat- 
ing clean iron with melted zinc, thus affording a protection much needed 
in and around large towns, where the sulphurous and sulphuric acids 
arising from the combustion of coal, and the acid emanations from various 
factories, greatly accelerate the corrosion of unprotected iron. The iron 
plates to be coated are first thoroughly cleansed by a process which will be 
more particularly noticed in the manufacture of tin-plate, and are then 



EXTRACTION OF ZINC. 293 

dipped into a vessel of melted zinc, the surface of which is coated with 
sal-arnmoniac (hydrochlorate of ammonia) in order to dissolve the oxide 
of zinc which forms upon the surface of the melted metal, and might 
adhere to the iron plate so as to prevent its becoming uniformly coated 
with the zinc* A more firmly adherent coating of zinc is obtained by 
first depositing a thin film of tin upon the surface of the iron plate by 
galvanic action, and hence the name of galvanised iron. 

The ores of zinc are found pretty abundantly in England, chiefly in the 
Mendip Hills in Somersetshire, at Alston Moor in Cumberland, in Corn- 
wall and Derbyshire, but the greater part of the zinc used in this country 
is imported from Belgium and Germany, being derived from the ores of 
Transylvania, Hungary, and Silesia. 

Metallic zinc is never met with in nature. Its chief ores are calamine 
or carbonate of zinc (ZnO.C0 2 ), blende or sulphide of zinc (ZnS), and 
red zinc ore, in which oxide of zinc (ZnO ) is associated with the oxides 
of iron and manganese. 

Calamine is so called from its tendency to form masses resembling a 
bundle of reeds (calamus, a reed). It is found in considerable quantities 
in Somersetshire, Cumberland, and Derbyshire. A compound of car- 
bonate with hydrate of zinc, ZnO.CO.,, 2(ZnO.H 2 0) is found abundantly 
in Spain. The mineral known as electric calamine is a silicate of zinc 
(2ZnO.Si0 2 .H.,0). Blende derives its name from the German blenden, 
to dazzle, in allusion to the brilliancy of its crystals, which are gene- 
rally almost black from the presence of sulphide of iron, the true colour 
of pure sulphide of zinc being white. Blende is found in Cornwall, Cum- 
berland, Derbyshire, Wales, and the Isle of Man, and is generally associated 
with galena or sulphide of lead, which is always carefully picked out of the 
ore before smelting it, since it would become converted into oxide of lead, 
which corrodes the earthen crucibles employed in the process. 

In England, the extraction of zinc from its ores is carried on chiefly at 
Swansea, Birmingham, and Sheffield. Before extracting the metal from 
these ores, they are subjected to a preliminary treatment which brings 
them both to the condition of oxide of zinc. For this purpose the cala- 
mine is simply calcined in a reverberatory furnace, in order to expel the 
carbonic acid ; but the blende is roasted for ten - or twelve hours, with con- 
stant stirring, so as to expose fresh surfaces to the air, when the sulphur 
passes off in the form of sulphurous acid, and its place is taken by the 
oxygen, the ZnS becoming ZnO. The extraction of the metal from this 
oxide of zinc depends upon the circumstance that zinc is capable of being- 
distilled at a bright red heat, its boiling point being 1904° E. 

The facility with which this metal passes off in the form of vapour is 
seen when it is melted in a ladle over a brisk fire, for at a bright red heat 
abundance of vapour rises from it, which, taking fire in the air, burns with 
a brilliant greenish white light, throwing off into the air numerous white 
flakes of light oxide of zinc (the philosopher's wool, or nil album of the 
old chemists). 

The distillation of zinc may be effected on the small scale in a black-lead crucible 
(A, fig. 241) about 5 inches high and 3 in diameter. A hole is drilled through the 
bottom with a round file, and into this is fitted a piece of wrought-iron gas-pipe (B) 
about 9 inches long and 1 inch wide, so as to reach nearly to the top of the inside of 

* The sal-ammoniac acts upon the heated zinc according to the equation, Zn + 
2(NH 3 .HC1) = ZnCl 2 + 2NH 3 + H 2 , and the chloride of zinc which is formed dissolves the 
oxide from the surface of the metal, producing an oxychloride of zinc. 



294 



EXTRACTION OF ZINC FROM ITS ORES. 



the crucible. Any crevices between the pipe and the sides of the hole are carefully 
stopped up with fire-clay moistened with solution of borax. A few ounces of zinc 
are introduced into the crucible, the cover of which is then carefully cemented on 
with fire-clay (a little borax being added to bind it together at a high temperature), 
and the hole in the cover is stopped up with fire-clay. The crucible having been 
kept for several hours in a warm place, so that the clay may dry, it is placed in a 
cylindrical furnace with a hole at the bottom, through which the iron pipe may pass, 
and a lateral opening into which is inserted an iron tube (C) connected with a torge 
bellows. Some lighted charcoal is thrown into the furnace, and when this has been 
blown into a blaze, the furnace is filled up with coke broken into small pieces. The 
fire is then blown till the zinc distils freely into a vessel of water placed for its recep- 
tion. Four ounces of zinc may be easily distilled in half-an-hour. 





Fig. 241.— Distillation of zinc. 



Fig. 242. — English zinc furnace. 



English method of extracting zinc. — The oxide of zinc, obtained as above 
from calamine or blende, is mixed with, about half its weight of coke or 
anthracite coal. This mixture is introduced into large crucibles (fig. 242) 
with a hole in the bottom, through which passes a short wide iron pipe 
destined for the passage of the vapour of zinc. These crucibles are about 
4 feet high by 2J feet wide. Some large pieces of coke are first intro- 
duced into them to prevent the charge from passing into the iron pipes, 
and when they have been charged with the above mixture, their covers 
are cemented on, and they are heated in furnaces somewhat resembling 
those of a glass-house, each furnace receiving six crucibles, which gene- 
rally contain, in all, one ton of roasted ore. When the mixture in the 
crucibles is heated to redness, it begins to evolve carbonic oxide, pro- 
duced by the combination of the carbon with the oxygen from the oxide 
of zinc. This gas burns with a blue flame at the mouth of the iron pipe ; 
but at a bright red heat the metallic zinc which has been thus liberated 
is converted into vapour, and the greenish-white flame of burning zinc 
is perceived at the orifice. When this is the case, about 8 feet of iron 
pipe are joined on to the short piece, in order to condense the vapour of 
zinc, which falls into a vessel placed for its reception. The distillation 
occupies about sixty hours, and the average yield is about 35 parts of 
zinc from 100 of ore, a considerable quantity of zinc being left behind 
in the form of silicate of zinc (electric calamine), which is not reduced 
by distillation with carbon. 



EXTRACTION OF ZINC FROM ITS ORES. 



295 




Fig. 243.— Belgian 
zinc furnace. 



The zinc thus obtained, however, is mixed with a considerable quantity 
of oxide of zinc, and with other foreign matters carried over from the 
crucibles. It is, therefore, again melted in a large iron pan, and allowed 
to rest, in order that the dross may rise to the surface ; this is skimmed 
off, to be worked over again in a fresh operation, and the metal is cast 
into ingots, which are sent into commerce under the name of spelter. 

Belgian process for the extraction of zinc. — At the Vieille-Montagne 
works, near Liege, calamine is exposed to the rain for several months in 
order to wash out the clay ; it is then calcined to 
expel the water and carbonic acid, the oxide of zinc so 
obtained being mixed with half its weight of coal dust, 
and distilled in fire-clay cylinders (C, fig. 243), hold- 
ing about 40 lbs. each, and set in seven tiers of six 
each in the same furnace, the vapour of zinc being con- 
veyed by a short conical iron pipe (B) into "a conical 
iron receiver (D), which is emptied every two hours 
into a large ladle, from which the zinc is poured into 
ingot-moulds. Each distillation occupies about twelve 
hours. The advantage of this particular mode of 
arranging the cylinders is, that it economises fuel by 
allowing the poorer ores, which require less heat to 
distil all the zinc from them, to be introduced into the 
upper rows of cylinders farthest from the fire (A). There 
are two varieties of Belgian ore, one containing 33 and 
the other 46 per cent, of zinc, but a large proportion of 
this is in the form of silicate, which is not extracted by the distillation. 

Silesian process for extracting zinc. — In Silesia, the oxide of zinc 
obtained by the calcination of calamine is mixed with fine cinders, and 
distilled in arched earthen retorts (A, fig. 244), into which the charge is 
introduced through a small 
door (B), which is then 
cemented up. These re- 
torts are arranged in a 
double row in the same 
furnace (fig. 245), and the 
vapour of zinc is condensed 
in a bent earthenware pipe a ttached to each retort, and having an open- 
ing (C) near the bend, 
which is kept closed, un- 
less it is necessary to clear 
out the pipe. In regard 
to the consumption of 
fuel, this process is far 
more economical than that 
followed in this country. 
The Silesian zinc is re- 
melted, before casting into 
ingots, in clay instead of 
iron pots, since melted 
zinc always dissolves iron, 
and a very small quantity of that metal is found to injure zinc when 
required for rolling into sheets. 

A small quantity of lead always distils over together with the zinc, 




Fig. 244. 




Silesian zinc furnace. 



296 PROPERTIES OF ZINC. 

and since this metal also interferes with the rolling of zinc into sheets, 
a portion of it is separated from zinc intended for this purpose, by melt- 
ing the spelter, in large quantity, upon the hearth of a reverberatory 
furnace, the bed of which is inclined so as to form a deep cavity at the 
end nearest the chimney. The specific gravity of lead being 11*4, 
whilst that of zinc is 6*9, the former accumulates chiefly at the bottom 
of the cavity, and the ingots cast from the upper part of the melted zinc 
will contain but little lead, since zinc is not able to dissolve more than 
1 '2 per cent, of that metal. 

Ingots of zinc, when broken across, exhibit a beautiful crystalline frac- 
ture, which, taken in conjunction with the bluish colour of the metal, 
enables it to be easily identified. 

The spelter of commerce is liable to contain lead, iron, tin, antimony, 
arsenic, copper, and cadmium. Belgian zinc is usually purer than the 
English metal. 

Zinc being easily dissolved by diluted acids, it is necessary to be care- 
ful in employing this metal for culinary purposes, since its soluble salts 
are poisonous. 

It will be remembered that the action of diluted sulphuric acid upon 
zinc is employed for the preparation of hydrogen. Pure zinc, however, 
evolves hydrogen very slowly, since it becomes covered with a number of 
hydrogen bubbles which protect it from further action ; but if a piece of 
copper or platinum be made to touch the zinc beneath the acid, these 
metals, being electronegative towards the zinc, will attract the electroposp 
tive hydrogen, leaving the zinc free from bubbles and exposed on all 
points to the action of the acid, so that a continuous disengagement of 
hydrogen is maintained. As a curious illustration of this, a thin sheet of 
platinum or silver foil may be shown to sink in diluted sulphuric acid, 
until it comes in contact with a piece of zinc, when the bubbles of hydro- 
gen bring it up to the surface. The lead, iron, &c, met with in commer- 
cial zinc, are electronegative to the zinc, and thus serve to maintain a con- 
stant evolution of hydrogen. 

A coating of metallic zinc may be deposited upon copper by slow gal- 
vanic action, if the copper be immersed in a concentrated solution of 
potash, at the boiling point of water, in contact with metallic zinc, when 
a portion of the latter is dissolved in the form of oxide, with evolution of 
hydrogen, and is afterwards precipitated on the surface of the electro- 
negative copper. 

Oxide of zinc (ZnO). — Zinc forms but one oxide, which is known in 
commerce as zinc-iffhite, and is prepared by allowing the vapour of the 
metal to burn in earthen chambers through which a current of air is 
maintained. This zinc-white is sometimes used for painting in place of 
white lead (carbonate of lead), over which it has the advantages of not 
injuring the health of the persons using it, and of being unaffected by 
sulphuretted hydrogen, an important consideration in manufacturing towns 
where that substance is so abundantly supplied to the atmosphere. Un- 
fortunately, however, the oxide of zinc does not combine with the oil of 
the paint, as oxide of lead does, and the paint is consequently more liable 
to peel off. The oxide of zinc has the characteristic property of becoming 
yellow when heated, and white again as it cools. It is sometimes used 
in the manufacture of glass for optical purposes. 

Oxide of zinc forms a soluble compound with potash, in this respect 
resembling alumina, and therefore metallic zinc, like aluminum, is dis- 



CADMIUM. 297 

solved by "boiling with solution of potash, hydrogen being disengaged 
from the water, the oxygen of which combines with the zinc. 

The sulphate of zinc or white vitriol, which is employed in medicine, 
and more extensively in calico-printing, is prepared by roasting blende 
(sulphide of zinc, ZnS) at a low temperature, when both its elements com- 
bine with oxygen, the oxide of zinc and sulphuric acid thus produced 
remaining in combination as sulphate of oxide of zinc (ZnO.S0 3 ). After 
roasting, the mass is treated with water, which dissolves the sulphate, and 
yields it again, on evaporation, in prismatic crystals having the formula 
ZnO.SO3.H5jO.6Aq. 

Chloride of zinc (ZnClJ, prepared by dissolving zinc in hydrochloric 
acid, is known in commerce as Burnett? s disinfecting fluid, since it is 
capable of absorbing hydrosulphuric acid, ammonia, and other offensive 
products of putrefaction, and arrests the decomposition of wood and 
animal substances. By evaporating its solution, the chloride of zinc is 
obtained in a fused state, and solidifies on cooling into white deliquescent 
masses. It has a very powerful attraction for water. 

CADMIUM. 

Cd" = 112 parts by weight.* 

209. This metal is found in small quantities in the ores of zinc, its 
presence being indicated during the extraction of that metal (p. 294) by 
the appearance of a brown flame {brown blaze) at the commencement of 
the distillation, before the characteristic zinc-flame is seen at the orifice 
of tie iron tube. Cadmium is more easily vaporised than zinc, boiling 
at 1580° F., so that the bulk of it is found in the first portions of the 
distilled metal. If the mixture of cadmium and zinc be dissolved 
in diluted sulphuric acid, and the solution treated with hydrosulphuric 
acid gas, a bright yellow precipitate of sulphide of cadmium (CdS) is 
obtained, which is employed in painting under the name of cadmia. By 
dissolving this in strong hydrochloric acid and adding carbonate of 
ammonia, the carbonate of cadmium (CdO.C0 2 ) is precipitated, from 
which metallic cadmium may be extracted by distillation with charcoal. 

Although resembling zinc in its volatility and its chemical relations, in 
appearance it is much more similar to tin, and' emits a crackling sound 
like that metal when bent. Like tin, also, it is malleable and ductile at 
the ordinary temperature, and becomes brittle at about 180° F. It is 
as fusible as tin, becoming liquid at 442° F., so that it is useful for 
making fusible alloys. An alloy of 3 parts of cadmium with 15 of bis- 
muth, 8 of lead, and 4 of tin, fuses at 140° F. In its behaviour with 
acids and alkalies cadmium is similar to zinc, but the metal is easily dis- 
tinguished from all others by its yielding a characteristic chestnut-brown 
oxide when heated in air. This oxide (CdO) is the only oxide of cadmium. 

The iodide of cadmium (Cdl 2 ), obtained by the action of iodine upon 
the metal in the presence of water, is employed in photography. 

Indium is the name of a metal which has recently been discovered, with the help 
of the spectroscope, in a specimen of blende from Freiberg. Its name refers to an 
indigo blue line in the spectrum. The examination of the metal is as yet imperfect, 
but it is white, malleable, and dissolves, like zinc and cadmium, in hydrochloric acid. 
Its specific gravity is 7 '36. To extract indium from the Freiberg zinc, the metal is 

* 112 parts by weight of cadmium, when converted into vapour, occupy twice the 
volume or' one part by weight of hydrogen, making it appear that its atomic weight should 
be 56, but the specific heat of cadmium, as well as its general chemical relations, favour 
the view that it is a di-atomic metal like zinc, its atomic weight being 112. 



298 



IRON. 



boiled with dilute sulphuric acid, employed in such quantity as to leave part of the 
zinc undissolved, together with indium and lead. The residue is dissolved in nitric 
acid, the lead and cadmium precipitated by hydrosulphuric acid, the latter expelled 
by boiling, and the oxide of indium precipitated from the solution by carbonate of 
baryta. When this precipitate is dissolved in hydrochloric acid, and excess of 
ammonia added, the white hydrated oxide of indium is precipitated, and may be 
reduced by heating in hydrogen. 

At a bright red heat it burns with a violet blue flame, yielding a yellow oxide of 
indium, InO. 

The atomic weight of indium appears to be about 72. 

210. Uranium. — This is a rare metal, never employed in the metallic state, but 
in the form of sesquioxide (U~ 2 3 ) and black oxide (2UO.U 2 3 ), for imparting 
yellow and black colours respectively to glass ' and porcelain. The chief source of 
these compounds is the mineral pitch-blende, which contains a large proportion of 
black oxide of uranium, together with silica, iron, copper, lead, and arsenic. In its 
chemical relations uranium presents some similarity to iron and manganese. It 
forms two distinct oxides, UO and U 2 3 , of which the former is decidedly basic, 
whilst the latter is capable of acting both as an acid and a base. The bright 
greenish-yellow colour of the salts of the sesquioxide of uranium is characteristic of 
the metal, and glass coloured with this oxide exhibits the remarkable optical effect 
of fluorescence in a very high degree. 

IEOK 

Fe" = 56 parts by weight. 

211. This most useful of all metals is one of those most widely and 
abundantly diffused in nature. It is to be found in nearly all forms of 
rock, clay, sand, and earth, its presence in these being commonly indi- 
cated by their colours, for iron is the commonest of natural mineral 
colouring ingredients. It is also found, though in small proportion, in 
plants, and in larger quantity in the bodies of animals, especially in the 
blood, which contains about 0*5 per cent, of iron in very intimate associ- 
ation with its colouring matter. 

But iron is very rarely found in the metallic state in nature, being 
almost invariably combined either with oxygen or sulphur. 

Metallic iron is met with, however, in the meteorites or metallic masses, 
sometimes of enormous size, and of unknown origin, which occasionally 
fall upon the earth. Of these iron is the chief component, but there are 
also generally present, cobalt, nickel, chromium, manganese, copper, tin, 
magnesium, carbon, phosphorus, and sulphur. 

The chief forms of combination in which iron is found in sufficient 
abundance to render them available as sources of the metal, are shown in 
the following table : — 

Ores of Iron. 



Common Name. 


Chemical Name. 


Composition. 


Magnetic iron ore 


Protosesquioxide of iron 


Fe 3 4 


Red haematite 


Sesquioxide of iron 


Fe 2 3 


Specular iron 


»> >> 


>> 


Brown haematite 


Hydrated sesquioxide 


2Fe a 8 .3H 2 


Spathic iron ore 


Carbonate of iron 


FeO.C0 2 


Clay iron-stone 


Carbonate of iron with clay 




Blackband 


{ Carbonate of iron with clay and 
\ bituminous matter 




Iron pyrites 


Bisulphide of iron 


FeS., 



OEES OF IRON. 



299 



These ores are frequently associated with extraneous minerals, some of 
the constituents of which are productive of injury to the quality of the 
iron. It is worthy of notice that scarcely one of the ores of iron is 
entirely free from sulphur and phosphorus, substances which will be seen 
to have a very serious influence on the quality of the iron extracted from 
them, and the presence of which increases the difficulty of obtaining the 
metal in a marketable condition. 

The following table illustrates the general composition of the most 
important English ores of iron, with reference to the proportions of iron, 
and of those substances which materially influence the character of the 
iron extracted from the ore, viz., manganese (present as oxide or car- 
bonate), phosphorus (present as phosphoric acid), and sulphur (present as 
bisulphide of iron). The maximum and minimum quantites found in 
each ore are specified. 



British Iron Ores. 



In 100 parts. 



Clay iron-stone from coal measures, 
Clay iron-stone from the lias, 
Brown hsematite, .... 
Red hsematite, 
Spathic ore, . 

Magnetic ore, 



Iron. 



43-30 
49-17 
6304 
6910 
4978 



20-95 
17-34 
11-98 
47-47 
13-98 



5701 



Oxide of 
Manganese. 



3 30 
1-30 
1-60 
1-13 
1264 



0-46 


trace 
trace 

1-93 



014 



Phosphoric 
Acid. 



Max. Min 



1-42 
5-05 
3-17 
trace 
0-22 



0-07 


trace 




Bisulphide 
of Iron. 
(Pyrites.) 



Max. Min 



1-21 
1-60 
0-30 
0-06 
0-11 



07 



No. of 
Samples 
Analysed. 



From this table it will be gathered that, among the most abundant of 
the iron ores of this country, red hsematite is the richest and purest, 
whilst the brown haematite often contains considerable proportions of 
sulphur and phosphorus, and the spathic ore, though containing little 
sulphur and phosphorus, often contains much manganese. 

The argillaceous ores, or clay iron-stones, found in the lias, contain more 
phosphoric acid than those from the coal-measures ; and these latter, as a 
general rule, contain more sulphur (pyrites) than the former, although the 
maximum in the table does not show this. 

Clay iron-stone is the ore from which the largest quantity of iron is 
extracted in England, since it is found abundantly in the coal-measures 
of Staffordshire, Shropshire, and South Wales, and it is a circumstance 
of great importance in the economy of English iron-smelting, that the 
coal and lime-stone required in the smelting process, and even the fire-clay 
employed in the construction of the furnace, are found in the immediate 
vicinity of the ore. 

Blackband is the clay iron-stone found in the coal-fields of Scotland, 
and often contains between 20 and 30 per cent, of bituminous matter, 
which contributes to the economy of fuel in smelting it. 

Red luematite (Fe. 2 3 ) is the most characteristic of the ores of iron, 
occurring in hard shining rounded masses, with a peculiar fibrous structure 
and a dark red-brown colour, whence the ore derives its name (at/xa, blood). 
It is found in considerable quantities in Lancashire and Cornwall, but 

* This table has been compiled from the analyses given in " Percy on Iron and Steel. " 



300 ORES OF IRON. 

unfortunately its very compact structure is an obstacle to its being smelted 
alone, so that it is generally mixed with some clay iron-stone, and hence 
the iron obtained is not so free from sulphur and phosphorus as if it were 
extracted from haematite alone. 

Red ochre is a soft variety of this ore, containing a little clay. 

Brown hcematite (2Fe 2 3 .3H 2 0) is found at Alston Moor (Cumber- 
land) and in Durham, but it is more abundant on the Continent, and is 
the source of most of the Belgian and French irons. Pea iron ore and 
yellow ochre are varieties of brown haematite. The Scotch ore which is 
called kidney-form clay iron-stone is really a hydrated sesquioxide of iron. 

Specular iron ore (Fe 2 3 ) (oligist ore or iron-glance), although of the 
same composition as red haematite, is very different from it in appearance, 
having a steel-grey colour and a brilliant metallic lustre. The island of 
Elba is the chief locality where this ore is found, but it also occurs in 
Germany, France, and Eussia. The excellent quality of the iron smelted 
from this ore is due partly to the purity of the ore, and partly to the cir- 
cumstance that charcoal, and not coal, is employed in smelting it. 

Magnetic iron ore (Fe 3 4 ), of which the loadstone is a variety, has a 
more granular structure, and a dark iron-grey colour. It forms moun- 
tainous masses in Sweden, and is also found in Eussia and North 
America. It is generally smelted with charcoal, and yields an excellent 
iron. Iron sand, a peculiar heavy black sand, of metallic lustre, con- 
sists in great measure of the magnetic ore, but contains a very large pro- 
portion of titanic acid. It is found abundantly in India, Nova Scotia, 
and New Zealand ; but its fine state of division prevents it from being 
largely available as a source of iron. 

Spathic iron ore (FeO.CO.J is found in abundance in Saxony, and 
often contains a considerable quantity of carbonate of manganese, which 
influences the character of the metal extracted from it. 

The oolitic iron ore, occurring in the Northampton oolite, contains both 
hydrated sesquioxide and carbonate of iron, together with clay. 

Iron pyrites (FeS 2 ) is remarkable for its yellow colour, its brilliant 
metallic lustre, and crystalline structure, being generally found either in 
distinct cubical or dodecahedral crystals, or in rounded nodules of 
radiated structure. It wa.s formerly disregarded as a source of iron, on 
account of the difficulty of separating the sulphur ; but since the demand 
for iron has so largely increased, an inferior quality of the metal has been 
extracted from the residue left after burning the pyrites in the manufac- 
ture of oil of vitriol (p. 205), the residue being first well roasted in a 
lime-kiln to remove as much as possible of the sulphur. 

212. Metallurgy of iron. — Iron owes the high position which it occupies 
among useful metals to a combination of valuable qualities not met with 
in any other. Although possessing nearly twice as great tenacity or strength 
as the strongest of the other metals commonly used in the metallic state, 
it is yet one of the lightest, its specific gravity being only 7*7, and is 
therefore particularly well adapted for the construction of bridges and 
large edifices, as well as for ships and carriages. It is the least yield- 
ing or malleable of the metals in common use, and can therefore be relied 
upon for affording a rigid support ; and yet its ductility, when heated, is 
such that it admits of being rolled into the thinnest sheets and drawn 
into the finest wire, the strength of which is so great that a wire of y^th 
inch in diameter is able to sustain 705 pounds, while a similar wire of 



EXTRACTION OF IRON FROM CLAY IRON-STONE. 301 

copper, which stands next in order of tenacity, will not support more 
than 385 pounds. 

Being, with the exception of platinum, the least fusible of useful metals, 
iron is applicable to the construction of fire-grates and furnaces. Nor are 
its qualifications all dependent upon its physical properties, for it not only 
enters into a great number of compounds which are of the utmost use in 
the arts, but its chemical relations to one of the non-metallic elements, 
carbon, are such, that the addition of a small quantity of this element 
converts it into steel, far surpassing iron in the valuable properties of hard- 
ness and elasticity; whilst a larger quantity of carbon gives rise to cast- 
iron, the greater fusibility of which permits it to be moulded into vessels 
and shapes which could not be produced by forging. 

213. English process of smelting clay iron-stone. — The first step 
towards the extraction of the metal consists in calcining (or roasting) the 
ore, in order to expel the water and carbonic acid which it contains. To 
effect this the ore is built up, together with a certain amount of small 
coal, into long pyramidal heaps, resting upon a foundation of large lumps 
of coal ; blackband often contains so much coal that any further addition 
is unnecessary. These heaps are kindled in several places, and allowed to 
burn slowly until all the fuel is consumed. This calcination has the effect 
of rendering the ore more porous, and better fitted for the smelting pro- 
cess. If the ore contained much sulphur, a part of it would be expelled 
by the roasting, in the form of sulphurous acid. 

Sometimes the calcination is effected in kilns resembling lime-kilns, 
and it is often altogether omitted as a separate process, the expulsion of 
the water and carbonic acid being then effected in the smelt ing-furnace 
itself as the ore descends. 

The calcined ore is smelted in a huge blast-furnace (fig.. 246) about fifty or 
sixty feet high, built of massive masonry, and lined internally with fire- 
brick. Since it would be impossible to obtain a sufficiently high tem- 
perature with the natural draught of this furnace, air is forced into it 
at the bottom, under a pressure of three or four pounds upon the inch, 
through three tuyere pipes, the nozzles of which pass through apertures in 
three sides of the furnace. 

It would be very easy to reduce to the metallic state the oxide of iron 
contained in the calcined ore, by simply throwing it into this furnace, 
together with a proper quantity of coal, coke, or charcoal; but the metallic 
iron fuses with so great difficulty, that it is impossible to separate it from 
the clay unless this latter is brought into a liquid state; and even then, the 
fusion of the iron, which is necessary for complete separation, is only 
effected after it has formed a more easily fusible compound with a small 
proportion of carbon derived from the fuel. 

ISTow, clay is even more difficult to fuse than iron, so that it is neces- 
sary to add, in the smelting of the ore, some substance capable of forming 
with the clay a combination which is fusible at the temperature of the 
furnace. If clay (silicate of alumina) be mixed with limestone (carbonate 
of lime), and exposed to a high temperature, the carbonic acid is expelled 
from the limestone, and the lime unites with the clay, forming a double 
silicate of alumina and lime, which becomes perfectly liquid, and when 
cool, solidifies to a glass or slag. The limestoue is here said to act as a 
flux, because it induces the clay to flow in the liquid state. In order, 
therefore, that the clay may be readily separated from the metallic iron, 



302 



BLAST-FURNACE FOR SMELTING IRON ORES. 



the calcined ore is mixed with a certain proportion of limestone before 
being introduced into the furnace. 

Great care is necessary in first lighting the blast-furnace lest the new 
masonry should be cracked by too sudden a rise of temperature, and when 
once lighted, the furnace is kept in constant work for years until in want of 
repair. When the fire has been lighted, the furnace is filled up with coke, 




Fig. 246.— Blast-furnace for smelting iron ores. 

and as soon as this has burnt down to some distance below the chimney, a 
layer of the mixture of calcined ore with the requisite proportion of lime- 
stone is thrown upon it ; over this there is placed another layer of coke, 
then a second layer of the mixture of ore and flux, and so on, in alternate 
layers, until the furnace has been filled up ; when the layers sink down, 
fresh quantities of fuel, ore, and flux are added, so that the furnace is kept 
constantly full. As the air passes from the tuyere pipes into the bottom 
of the furnace, it parts with its oxygen to the carbon of the fuel, which 
it converts into carbonic acid (C0 2 ) ; the latter, passing over the red-hot 
fuel as it ascends in the furnace, is converted into carbonic oxide (CO) by 
combining with an additional quantity of carbon. It is this carbonic 
oxide which reduces the calcined ore to the metallic state, when it comes 
in contact with it, at a red heat, in the upper part of the furnace, for 
carbonic oxide removes the oxygen, at a high temperature, from the oxides 
of iron, and becomes carbonic acid, the iron being left in the metallic 
state. But the iron so reduced remains disseminated through the mass 



CHEMICAL CHANGES IN THE BLAST-FURNACE. 303 

of ore until it has passed down to a part of the furnace which is more 
strongly heated, where the iron enters into combination with a small pro- 
portion of carbon to form cast-iron, which fuses and runs down into the 
crucible or cavity for its reception at the bottom of the furnace. At the 
"same time, the clay contained in the ore is acted upon by the lime of the 
flux, producing a double silicate of alumina and lime, which also falls 
in the liquid state into the crucible, where it forms a layer of " slag " 
above the heavier metal. This slag, which has five or six times the bulk 
of the iron, is allowed to accumulate in the crucible, and to run over 
its edge down the incline upon which the blast-furnace is built; but 
when a sufficient quantity of cast-iron has collected at the bottom of 
the crucible, it is run out through a hole provided for the purpose, either 
into channels made in a bed of sand, or into iron moulds, where it is cast 
into rough semi-cylindrical masses called pigs, whence cast-iron is also 
spoken of as pig-iron. The temperature of the furnace is, of course, 
highest in the immediate neighbourhood of the tuyeres ; the reduction of 
the iron to the metallic state appears to commence at about two-thirds of 
the way down the furnace, the volatile matters of the ore, fuel, and flux 
being driven off before this point is reached. 

Some idea may be formed of the immense scale upon which the smelt- 
ing of iron ores is carried out, when it is stated that each furnace con- 
sumes, in the course of twenty-four hours, about 50 tons of coal, 30 tons 
of ore, 6 tons of limestone, and 100 tons of air. The cast-iron is run off 
from the crucible once or twice in twelve hours, in quantities of five 
or six tons at a time. The average yield of calcined clay iron-stone is 35 
per cent, of iron. 

The gases escaping from the chimney of the blast-furuace are highly 
inflammable, for they contain, beside the nitrogen of the air blown into the 
furnace, a considerable quantity of carbonic oxide and some hydrogen, 
together with the carbonic acid formed by the action of the carbonic oxide 
upon the ore. Since the carbonic oxide and hydrogen confer considerable 
heating power upon these gases, they are employed in some iron-works 
for heating steam-boilers, or for calcining the ore, or for raising the tem- 
perature of the blast. 

The composition of the gas issuing from a hot-blast furnace (fed with uncoked 
coal) may be judged of from the following table : — 

Gas from Blast- Furnace. 

Nitrogen, . 
Carbonic oxide, 
Hydrogen, . 
Carbonic acid, 
Marsh -gas, . 
Oleiiant-gas, 









55-35 vols 








25-97 ,, 








6-73 ,, 








7-77 „ 








3-75 ,, 








0-43 ,, 



100-00 



The carbonic oxide, of course, renders these gases highly poisonous, and fatal acci- 
dents occasionally happen from this cause. 

Although the bulk of the nitrogen present in the air escapes unchanged from the 
furnace, it is not improbable that a portion of it contributes to the formation of the 
cyanide of potassium (KCN), which is produced in the lower part of the furnace, the 
potassium being furnished by the ashes of the fuel. 

The hot-blast. — On considering the enormous quantity of air which 
passes through the blast furnace, it will be seen that it occasions the loss 
of a considerable amount of heat. In order to economise the fuel, hot- 



304 HOT-BLAST IRON. 

blast furnaces are fed with air of which the temperature is raised to about 
600° F., by passing it through heated iron pipes before allowing it to 
enter the blast furnace. The higher temperature which is thus attained 
permits the use of uncoked coal, which would not have given enough heat 
in a cold-blast furnace, and the same quantity of ore may be smelted with 
less than half the coal formerly employed. It appears, however, that the 
hot-Mast iron is inferior in quality to that obtained from the same ore in a 
cold-blast furnace, and this is generally explained by referring to the 
larger quantity of sulphur contained in the raw coal ; to the circumstance, 
that the cast-iron being exposed to a much higher temperature in the hot- 
blast furnace is more liable to receive and retain a larger amount of foreign 
substances ; and (most important of all) to the custom of extracting iron 
in a hot-blast furnace from slags obtained in the subsequent processes of 
the iron-manufacture, which could not be smelted in a cold-blast furnace. 
These slags always contain sulphur and phosphorus, and therefore yield an 
inferior quality of iron. Hence the distinction commonly drawn between 
mine-iron extracted from the ore without admixture of slags, and cinder- 
iron in the preparation of which slag or cinder has been employed. 

The slag from the blast-furnace is essentially a glass composed of a 
double silicate of alumina and lime, the composition of which varies much 
according to the nature of the earthy matters in the ore, and the com- 
position of the flux. Its colour is generally opaque white, streaked with 
blue, green, or brown. 

The nature of the flux employed must, of course, be modified according 
to the composition of the earthy substances (or gangue) present in the ore. 
Where this consists of clay (silicate of alumina) the addition of lime 
(which is sometimes added in the form of limestone and sometimes as 
quick-lime) will provide for the formation of the double silicate of alumina 
and lime. But if the iron-ore happened already to contain limestone, an 
addition of clay would be necessary, or if quartz were present, consisting 
of silica only, both lime and alumina (in the form of clay) will be neces- 
sary as a flux. It is sometimes found economical to employ a mixture of 
ores containing different kinds of gangue, so that one may serve as a flux 
to the other. If a proper proportion of lime were not added, a portion of 
the oxide of iron would combine with the silica and be carried off in the 
slag, but if too large a quantity of lime be employed, it will diminish the 
fusibility of the slag, and prevent the complete separation of the iron from 
the earthy matter. The most easily fusible slag which can be formed by 
the action of lime upon clay has the composition 6CaO.Al 2 3 .9Si0 2 ; but, 
in English furnaces, where coal and coke are employed, it is found neces- 
sary to employ a larger proportion of lime to convert the sulphur of the 
fuel into sulphide of calcium, so that the slag commonly has a composi- 
tion more nearly represented by the formula, 12Ca0.2Al 2 3 .9Si0 2 , which 
would express a compound of 6 molecules of normal silicate of lime with 
1 molecule of normal silicate of alumina, 6(2CaO.Si0 2 ), 2Al 2 3 .3Si0 2 , 
silicic acid being considered a bibasic acid. 

Since iron, manganese, and magnesium are commonly found occupying 
the place of a portion of the calcium, a more general formula for the slag 
from English blast furnaces would be — 

6(2[CaFeMnMg]O.Si0 2 ), 2Al 2 3 .3Si0 2 . 

A fair impression of the ordinary composition of the slag from blast 
furnaces is conveyed by the following table : — 



CAST-IRON. 




Slag from Blast Furnace. 




Silica, . . . 


43-07 


Alumina, 






14-85 


Lime, .... 






28-92 


Magnesia, 






5-87 


Oxide of iron (FeO), 






2-35 


Oxide of manganese (MnO), 






1-37 


Potash, 






1-84 


Sulphide of calcium, 






1-90 


Phosphoric acid, 






trace 



305 



100-35 

These slags are sometimes run from the blast furnace into iron moulds, 
in which they are cast into blocks for rough building purposes. The 
presence of a considerable proportion of potash has led to experiments 
upon their employment as a manure, for which purpose they have been 
blown out, when liquid, into a finely divided frothy condition fit for 
grinding and applying to the soil. 

214. Cast-Iron is, essentially, composed of iron with from 2 to 5 per 
cent, of carbon, but always contains other substances derived either from 
the ore or from the fuel employed in smelting it. On taking into con- 
sideration the energetic deoxidising action in the blast furnace, it is not 
surprising that portions o* the various oxygen compounds exposed to it 
should part with their oxygen, and that the elements thus liberated 
should find their way into the cast-iron. In this way the silicic acid is 
reduced, and its silicon is found in cast-iron in quantity sometimes amount- 
ing to 3 or 4 per cent. Sulphur and phosphorus are also generally pre- 
sent in cast-iron, but in very much smaller quantity; their presence 
diminishes its tenacity, and the smelter endeavours to exclude them as far 
as possible, though a small quantity of phosphorus appears to be rather 
advantageous for some castings, since it augments the fusibility and 
fluidity of the cast-iron. The sulphur is chiefly derived from the coal or 
coke employed in smelting, and for this reason charcoal would be pre- 
ferable to any other fuel if it could be obtained at a sufficiently cheap 
rate. The iron-works of America and those of the European continent 
enjoy a great advantage in this respect over 'those of England. The 
phosphorus is obtained chiefly from the phosphoric acid existing in the 
ore or in the flux. Manganese, amounting to 1 or 2 per cent., is often met 
with in cast-iron, having been reduced from the oxide of manganese, which 
is generally found in iron ores. Other metals, such as chromium, cobalt, 
&c, are also occasionally present, though in so small quantities as to be 
of no importance in practice. 

The following table exhibits the largest and smallest proportions of the 
various elements determined in the analysis of upwards of a hundred 
specimens of cast-iron : — 





Composition of Cast-iron. 


* 




Maximum. 


Minimum. 


Carbon, . 


4-81 


1 -04 per cent 


Silicon, 


4-77 


0-08 „ 


Sulphur, . 


1-06 


o-oo 


Phosphorus, 


1-87 


trace ,, 


Manganese, 


6-08 


trace , , 


Iron, 







Compiled from " Percy on Iron and Steel. 



306 



GREY, MOTTLED, AND WHITE IRON. 



In order to understand the difference observed in the several varieties 
of cast-iron, it is necessary to consider the peculiar relations between iron 
and carbon. Iron fused in contact with carbon is capable of combining 
with nearly 6 per cent, of that element, to form a white, brilliant, and 
brittle compound, which may be represented pretty nearly as composed 
of Fe 4 C. Under certain circumstances, as this compound of iron and 
carbon cools, a portion of the carbon separates from the iron, and remains 
disseminated throughout the mass in the form of minute crystalline par- 
ticles very much resembling natural graphite. If a broken piece of iron 
containing these scales be examined, the fracture will be found to exhibit 
a more or less dark grey colour, due to the presence of the uncombined 
carbon, and for this reason a cast-iron in which a portion of the carbon 
has thus separated is commonly spoken of as grey iron, whilst that in 
which the whole of the carbon has remained in combination with the 
metal, exhibits a white fracture, and is termed white iron or bright iron. 
Intermediate between these is the variety known as mottled iron, which 
has the appearance of a mixture of the grey and white varieties. 

The different condition of the carbon in the two varieties of cast-iron is 
rendered apparent when the metal is dissolved in diluted sulphuric or 
hydrochloric acid, for any carbon which exists in the uncombined state 
will then be left, whilst that which had been in combination with the 
iron passes off in the form of peculiar compounds of carbon and hydrogen, 
which impart the disagreeable odour perceived in the gas evolved when 
the metal is dissolved in an acid. 

The properties of these two varieties of cast iron are widely different, 
grey iron being so soft that it may be turned in a lathe, whilst the white 
iron is extremely hard, and of higher specific gravity. Again, although 
white iron fuses at a lower temperature than grey iron, the latter is far 
more liquid when fused, and is therefore much better fitted for casting. 

Although the presence of uncombined carbon is the chief point which 
distinguishes grey from white iron, other differences are commonly observed 
in the composition of the two varieties. The white iron usually contains 
less silicon than grey iron, but a larger proportion of sulphur. White 
iron also usually contains a much larger quantity of manganese. 

The difference in the composition of these three varieties of cast-iron is 
shown in the following table : — 





Grey. 


Mottled. 


White. 


Iron, .... 


90-24 


89-31 


89-86 


Combined carbon, 


1-02 


I 1-79 


2-46 


Graphite, 


2-64 


1-11 


0-87 


Silicon, 


3-06 


2-17 


1-12 


Sulphur, 


1-14 


1-48 


2-52 


Phosphorus, . 


0-93 


1-17 


0-91 


Manganese, . 


0-83 


1-60 


2-72 


99-86 


98-63 


100-46 



As might be expected, it is not easy to tell where a cast-iron ceases to 
be grey and begins to be mottled, or where the mottled iron ends and 



REFINING CAST-IRON. 307 

white iron begins. There are, in fact, eight varieties of cast-iron in com- 
merce, distinguished by the numbers one to eight, of which No. 1 is dark 
grey, and contains the largest proportion of graphite, which diminishes in 
the succeeding numbers up to No. 8, which is the whitest iron, the inter- 
mediate numbers being more or less mottled. 

The particular variety of cast-iron produced is to some extent under 
the control of the smelter, a furnace in good order appearing usually to 
yield grey iron, whilst a defective furnace, or one supplied with too small 
a proportion of fuel, will commonly give a white iron. But the metal 
sometimes varies considerably at different levels in the cmcible of the 
furnace, so that pigs of different degrees of greyness are obtained at the 
same tapping. 

Mottled cast-iron surpasses both the other varieties in tenacity, and 
is therefore preferred for such purposes as casting ordnance, where this 
quality is particularly desirable. 

The dark grey iron used for casting, known as foundry-iron, is produced 
at a higher temperature, by supplying the blast furnace with a larger pro- 
portion of fuel than is employed in making the lighter forge-iron destined 
for conversion into wrought-iron. The extra consumption of fuel, of 
course, renders the foundry-iron more expensive. When a furnace is 
worked with a low charge of fuel to produce a white iron, a larger quan- 
tity of iron is lost in the slag, sometimes amounting to 5 per cent, of 
the metal, whilst the average loss in producing grey iron does not exceed 
2 per cent. Ores containing a large proportion of manganese are generally 
found to yield a white iron. 

When grey iron is melted, the particles of graphite to which its grey 
colour is due are dissolved by the liquid iron, and if it be poured into 
a cold iron mould so as to solidify it as rapidly as possible, the external 
portion of the casting will present much of the hardness and appear- 
ance of white iron, the sudden cooling having prevented the separation 
of the graphite. This affords the explanation of the process of chill- 
casting, by which shot, &c, made of the soft fusible grey iron, are made 
to acquire externally a hardness approaching that of steel. 

The specific gravity of cast-iron varies between 6 '92 (grey) and 7*53 
(white), and its fusing point is somewhat below "3000° F. 



Conversion of Cast-Iron into Bar or Wrought Iron. 

215. In order to convert cast-iron into bar-iron, it is necessary to reduce 
it as far as possible to the condition of pure iron, by removing the carbon, 
silicon, and other substances associated with it. This purification is 
effected upon the principle, that when cast-iron is strongly heated in con- 
tact with oxide of iron, its carbon is evolved in the form of carbonic oxide, 
whilst the silicon, also combining with the oxygen from a part of the 
oxide of iron, is converted into silicic acid, which unites with an- 
other portion of oxide to form a fusible slag easily separated from the 
metal. 

The most important of the processes employed for the conver- 
sion of pig-iron into bar-iron, is that known as the puddling process, 
but this is sometimes preceded by the process of refining, which will 
therefore be first described. 

Refining cast-iron. — This process consists essentially in exposing the 



308 



REFINING CAST-IRON. 




Fig. 247. — Hearth for refining pig-iron. 



metal, in a fused state, to the action of a blast of air. The refinery 
(figs. 247, 248) is a rectangular trough with double walls of cast-iron, 
between which cold water is kept circulating to prevent their fusion. 
This trough is about 3J feet long by 2J wide, and usually lined 

with fire-clay; on each 
side of it are arranged 
three tuyere pipes for the 
supply of air, inclined at 
an angle of 25° to 30° to 
the bottom of the fur- 
nace, which is fed with 
coke, unless the very best 
iron is required, as for 
the manufacture of tin- 
plate, when charcoal is 
generally used in the 
refinery. 

This furnace having 
been filled to a certain 



height with fuel, five or 
six pigs of iron (from 
20 to 30 cwt.) are ar- 
ranged symmetrically 
upon it, and covered with coke, a blast of air being forced in through the 
tuyeres, under a pressure of about 3 lbs. upon the inch. In about a 
quarter of an hour the metal begins to fuse gradually, and to trickle down 

through the fuel to the 
bottom of the refinery, 
a portion of the iron 
being converted into 
oxide in its descent, by 
the air issuing from the 
tuyere pipes. When the 
whole of the metal has 
been f used, the air is still 
allowed to play for some 
time upon its surface, 
when the fused metal 
appears to boil in con- 
sequence of the escape 
of bubbles of carbonic 
oxide. 

After about two hours 
the tap hole is opened, and the molten metal run out into a flat cast-iron 
mould kept cold by water, in order to chill the metal and render it brittle. 
The plate of refined iron thus obtained is usually about 2 inches thick. The 
slag (or finery cinder) is generally received in a separate mould ; its com- 
position may be generally expressed by the formula 2FeO.Si0 2 , the silicic 
acid having been derived from the silicon contained in the cast-iron. 

The change effected in the composition of the iron by the process of 
refining will be apparent from the following table : — 




Hearth for refining 



THE PUDDLING PROCESS. 



309 



Refined Iron. 



Iron, 

Carbon, 

Silicon, 

Sulphur, 

Phosphorus, 

Manganese, 

Slag, . 



95-14 
3-07 
0-63 
0-16 
0-73 

trace 
0-44 

10017 



The carbon, therefore, is not nearly so much diminished as the silicon, 
which is in some cases reduced to x^-th of its former proportion by the 
refining process. Half of the sulphur is also sometimes removed, being 
found in the slag as sulphide of iron. The phosphorus is not removed to 
the same extent in the refining process, though some of it is converted 
into phosphoric acid, which may be found in the finery cinder. 

The further purification of the metal could not be effected in the 
refinery, since the fusibility of the iron is so greatly diminished as it 
approaches to a pure state, that it could not be retained in a fluid condi- 
tion at the temperature attainable in this furnace, and a more spacious 
hearth is required upon which the pasty metal may be kneaded into close 
contact with the oxide of iron which is to complete the oxidation and 
separation of the carbon. For this reason the metal is transferred to the 
puddling furnace. 

The puddling process is carried out in a reverberatory furnace (figs. 249, 
250) connected with a tall chimney provided with a damper, so as to admit 
of a very perfect regulation of the draught. A bridge of fire-brick between 




Fig. 249. — Puddling furnace. 

the grate and the hearth prevents the contact of the coal with the iron to 
be puddled. The hearth is composed either of fire-brick or of cast-iron 
plates, covered with a layer of very infusible slag, and cooled by a free 
circulation of air beneath them. This hearth is about 6 feet in length, by 
4 feet in the widest part near the grate, and 2 feet at the opposite end ; 
it is slightly inclined towards the end farthest from the grate, and finishes 
in a very considerable slope, at the lowest point of which is the floss-hole 
for the removal of the slag. Since the metal is to attain a very high 
temperature in this furnace (estimated at 3000° F.), it is usually covered 



310 



THE PUDDLING PKOCESS. 



with, an iron casing, so as to prevent any entrance of cold air through 
chinks in the brick work. 

About 5 cwt. of the fine metal is broken up and heaped upon the 
hearth of this furnace, together with about 1 cwt. of iron scales (black 




Fig. 250. — Puddling furnace. 

oxide of iron, Fe 3 4 ), and of hammer-slag (basic silicate of iron, obtained 
in subsequent operations), which are added in order to assist in oxidising 
the impurities. When the metal has fused, the mass is well stirred or 
puddled, so that the oxide of iron may be brought into contact with 
every part of the metal, to effect the oxidation of the impurities. The 
metal now appears to boil, in consequence of the escape of carbonic oxide, 
and in about an hour from the commencement of the puddling, so much 
of the carbon has been removed that the fusibility of the metal is con- 
siderably diminished, and instead of retaining a fused condition at the 
temperature prevailing in the furnace, it assumes a granular, sandy, or dry 
state, spongy masses of pure iron separating or coming to nature in the 
fused mass. The puddling of the iron is continued until the whole has 
assumed this granular appearance, when the evolution of carbonic oxide 
ceases almost entirely, showing that the removal of the carbon is nearly 
completed. The damper is now gradually raised, so as to increase the 
temperature and soften the particles of iron, in order that they may be 
collected into a mass ; and the more easily to effect this, a part of the 
slag is run off through the floss-hole. The workman, then collects some 
of the iron upon the end of the paddle, and rolls it about on the hearth 
until he has collected a sort of rough ball of iron, weighing about half-a- 
hundred weight. When all the iron has been collected into balls in this 
way, they are placed in the hottest part of the furnace, and pressed occa- 
sionally with the paddle, so as to squeeze out a portion of the slag with 
which their interstices are filled. The doors are then closed to raise the 
interior of the furnace to a very high temperature, and after a short time, 
when the balls are sufficiently heated, they are removed from the furnace, 
and placed under a steam hammer, which squeezes out the liquid slag, 
and forces the softened particles of iron to cohere into a continuous oblong 
mass or bloom, which is then passed between rollers by which it is ex- 
tended into bars. These bars, however (Rough or Puddled, or No. 1 Bar), 
are always hard and brittle, and are only fit for such constructions as rail- 
way bars, where hardness is required rather than great tenacity. In order 
to improve this latter quality, the rough bars are cut up into short lengths, 



TAP-CINDER FROM PUDDLING FURNACE. 



311 



which are made into bundles, and after being raised to a high tempera- 
ture in the mill-furnace, are passed through rollers, which weld the 
several bars into one compound bar, to be subsequently passed through 
other rollers until it has acquired the desired dimensions. By thus fagot- 
ting or piling the bars, their texture is rendered far more uniform, and 
they are made to assume a fibrous structure, which greatly increases 
their strength {Merchant Bar, or No. 2 Bar). To obtain the best, or No. 
3 Bar, or wire-iron, these bars are doubled upon themselves, raised to a 
welding heat, and again passed between rollers. These repeated rollings 
have the effect of thoroughly squeezing out the slag which is mechanically 
entangled among the particles of iron in the rough bars, and would pro- 
duce flaws if allowed to remain in the metal. A slight improvement 
appears also to be effected in the chemical composition of the iron during 
the rolling, some of the carbon, silicon, phosphorus, and sulphur, still 
retained by the puddled iron, becoming oxidised, and passing away as 
carbonic oxide and slag. 

The following table exhibits the change in chemical composition which 
takes place in pig-iron when puddled (without previous refining) and 
rolled into wire-iron : — 



Effect of Puddling and Forging on Cast-iron. 



In 100 parts. 


Carbon. 


Silicon. 


Sulphur. 


Phosphorus. 


Grey pig-iron, 
Puddled bar, 
Wire-iron, . 


2-275 
0-296 
0-111 


2-720 
0-120 . 
0-088 


0-301 
0-134 
0-094 


0-645 
0-139 
0-117 



About 90 parts of bar-iron are obtained from 100 of refined iron by the 
puddling process, the difference representing the carbon which has passed 
off as carbonic oxide, and the silicon, sulphur, phosphorus, and iron, 
which have been removed in the slag, or tap-cinder, this being essentially 
a silicate of protoxide and sesquioxide of iron, varying much in composi- 
tion according to the character of the iron employed for puddling, and the 
proportions of iron-scale and hammer-slag introduced into the furnace. 
Of course, also, the material of which the hearth is composed will in- 



fluence the composition of the slag, 
tration of its composition : — 



The following table affords an illus- 



Taj> Cinder from Puddlirig Fui 

Protoxide of iron (FeO), 
Peroxide of iron (Fe 2 3 ), ; 
Silicic acid, . 
Phosphoric acid, 
Sulphide of iron, . 
Lime, .... 
Oxide of manganese, 
Magnesia, 



nace. 



57-67 
13-53 
8-32 
7-29 
7-07 
4-70 
0-78 
0-26 

99-62 



The lime in the above cinder was probably derived from the hearth of 
the furnace, which is sometimes lined with that material to assist in re- 
moving the sulphur. 



312 



THE BESSEMER PROCESS. 



When pig-iron is puddled without undergoing the refining process, it 
becomes much more liquid than refined iron, and the process is some- 
times described as the boiling process, -whilst refined iron undergoes dry 
puddling. 

It will be observed that this process of puddling is attended with some 
important disadvantages ; it involves a great expenditure of manual labour, 
and of a most exhausting kind ; the very high temperature to which the 
puddler is exposed renders him liable to lung disease, and cataract is not 
uncommonly caused by the intense light from the glowing iron ; the wear 
and tear of the puddling furnace is very considerable, and since it receives 
only ten or eleven charges of about five cwts. each in the course of twenty- 
four hours, it is necessary to work five or six puddling furnaces at once, 
in. order to convert into bar-iron the whole of the cast-iron turned out 
from a single blast furnace. These considerations have led to several 
attempts to improve the puddling process by employing revolving furnaces 
and other mechanical arrangements to supersede the heavy manual labour, 
and even to dispense with it altogether by forcing the air into the molten 
iron. The most generally known of the processes devised for this purpose 
is that of Bessemer, which consists in running the melted cast-iron into a 
huge crucible, and forcing air up through it under considerable pressure, 
thus combining the purifying influence of the blast of air in the refinery 
with the mechanical agitation effected in the puddling furnace. Besse- 

mer's converting vessel (fig 251) is a 
large, nearly cylindrical crucible of 
wrought iron, lined with fire-clay, 
having apertures (A) at the bottom, 
through which air is blown at a 
pressure of fifteen or twenty pounds 
upon the inch. This vessel is some- 
times large enough to receive ten 
tons of cast-iron for a charge. The 
metal having been melted in a sepa- 
rate furnace, is run into the convert- 
ing vessel, the blast being already 
turned on so that the liquid iron may not run into the air tubes. The iron 
burns vividly, and the oxide of iron produced is diffused in a melted state 
through the mass of metal by the rapid current of air. This oxide of 
iron acts upon the silicon and carbon in the cast-iron, converting the 
latter into carbonic oxide, which burns with flame at the mouth of the 
converter, and the former into silicic acid, which enters into the slag, and 
is carried up as a froth to the surface of the liquid iron. The blast of air 
or blow is continued for about twenty minutes, when the disappearance of 
the flame of carbonic oxide indicates the completion of the process ; but the 
remaining purified iron is not pasty, as in the puddling furnace, being 
retained in a perfectly liquid condition by the high temperature resulting 
from the combustion of part of the iron, so that the metal may be run out 
into moulds by tilting the converting vessel, which is usually hung upon 
trunnions. In this way about 85 parts of bar- iron are obtained from 100 
of pig-iron. 

Although so great an economy of time and labour would result from the 
application of Bessemer's process, it has not superseded the puddling pro- 
cess, because it does not remove the sulphur and phosphorus from the 
pig-iron, so that only the best varieties of that material, extracted from 




Fig. 251. — Bessemer's converting vessel. 



COMPOSITION OF BAR-IRON. 



313 



haematite or magnetic ore, yield a bar-iron of good quality when purified 
in this way. Moreover, the process is applicable only to grey iron rich in 
carbon and silicon, which is more expensive than the light forge irons 
treated in the puddling furnace. Its application to the manufacture of 
steel will be noticed hereafter. The effect of the Bessemer process upon a 
particular specimen of pig-iron is shown in the table — 



Tn 100 parts of Pig-iron. 


Before. 


After. 


Carbon, ..... 
Silicon, ..... 
Sulphur, .... 
Phosphorus, . . . . 


3-309 
0-595 
0-485 
1-012 


0-218 
none 
0-402 
1-102 



Composition of bar-iron. — Even the best bar-iron contains from 0T to 
0*3 per cent, of carbon, together with minute proportions of silicon, sul- 
phur, and phosphorus. Perfectly pure iron is inferior in hardness and 
tenacity to that which contains a small proportion of carbon. 

Bar-iron is liable to two important defects, which are technically known 
as cold-shortness and red-shortness. Cold-short iron is brittle at ordinary 
temperatures, and appears to owe this to the presence of phosphorus, of 
which element "5 per cent, is sufficient materially to diminish the tenacity 
of the iron. When the iron is liable to brittleness at a red heat, it is 
termed red-short iron, and a very little sulphur is sufficient to affect the 
quality of the iron in this respect. 

There is much difference of opinion as to the true causes of the varia- 
tion in the strength of wrcught-iron, and this is not surprising when we 
reflect upon the number of circumstances which may be reasonally ex- 
pected to exert some influence upon it. Not only the proportions of 
carbon, silicon, sulphur, phosphorus, and manganese may be supposed to 
affect the quality of the iron, but the state of combination in which these 
elements exist in the mass is not unlikely to cause a difference. It also 
appears certain that the mechanical structure, "dependent upon the ar- 
rangement of the particles composing the mass of metal, has at least as 
much influence upon the tenacity of the iron as its chemical composition. 

The best bar-iron, if broken slowly, always exhibits a fibrous structure, 
the particles of iron being arranged in parallel lines. This appears to con- 
tribute greatly to the strength of the iron, for when it is wanting, and the 
bar is composed of a confused mass of crystals, it is weaker in proportion 
to the size of the crystals. The presence of phosphorus is said to favour 
the formation of large crystals, and hence to produce cold-shortness. There 
is some reason to believe that the fibrous is sometimes exchanged for the 
crystalline texture under the influence of frequent vibrations, as in the 
case of railway axles, girders of suspension-bridges, &c. 

Considering the difficult fusibility of bar-iron, it is fortunate that it 
possesses the property of being welded, that is, of being united by ham- 
mering when softened by heat. It is customary first to sprinkle the 
heated bars with sand or clay in order to convert the superficial oxide of 
iron into a liquid silicate, which will be forced out from between them by 
hammering or rolling, leaving the clean metallic surfaces to adhere. Burnt 
iron does not weld, and is largely crystalline in structure. 



314 



PRODUCTION OF STEEL BY CEMENTATION. 



Manufacture of Steel. 

216. Steel differs from bar-iron in possessing the property of becoming 
very hard and brittle when heated to redness and then suddenly cooled 
by being plunged into water. Perfectly pure iron, obtained by the elec- 
trotype process, is not hardened by sudden cooling; but all bar-iron 
which contains carbon does exhibit this property in a greater or less 
degree according to the proportion of carbon present. It does not become 
decidedly steely, however, until the carbon amounts to 0*3 per cent. The 
hardest steel contains about 1 *2 per cent, of carbon, and when the propor- 
tion reaches 1*4 per cent, it begins to assume the properties of white cast- 
iron. Bar-iron may, therefore, be converted into steel by the addition of 
about one per cent, of carbon, and, conversely, cast-iron is converted into 
steel when the quantity of carbon contained in it is reduced to that amount. 
There are thus two processes by which steel may be produced ; but that 
which is employed almost exclusively in this country consists in combin- 
ing bar-iron with the requisite amount of carbon by what is technically 
known as cementation, the bars being imbedded in charcoal and exposed 
for several days to a high temperature. 

The operation is effected in large chests of fire-brick or stone, about 10 
or 12 feet long by 3 feet wide and 3 feet deep. 




Fig. 252.— Furnace for converting bar-iron into steel. 

Two of these chests are built into a dome-shaped furnace {converting 
furnace, fig. 252), so that the flame may circulate round them, and the 
furnace is surrounded with a conical jacket of brick-work in order to allow 
a steady temperature to be maintained in it for some days. The charcoal 
is ground so as to pass through a sieve of \ inch mesh, and spread in an 
even layer upon the bottom of the chests. Upon this the bars of iron, 
which must be of the best quality, are laid in regular order, a small in- 
terval being left between them, which is afterwards filled in with the 
charcoal powder, with a layer of which the bars are now covered ; over 
this more bars are laid, then another layer of charcoal, and so on until the 
chest is filled. Each chest holds 5 or 6 tons of bars. One of the bars is 
allowed to project through an opening in the end of the chest, so that 
the workmen may withdraw it from time to time and judge of the progress 
of the operation. The whole is covered in with a layer of about 6 inches 
of damp clay or sand. 



BLISTEKED STEEL. 315 

The lire is carefully and gradually lighted, lest the chests should be 
split by too sudden application of heat, and the temperature is eventually 
raised to about the fusing point of copper (2000° F.), at which it is main- 
tained for a period varying with the quality of steel which it is desired to 
obtain. Six or eight days suffice to produce steel of moderate hardness ; 
but the process is continued for three or four days longer if very hard 
steel be required. The fire is gradually extinguished, so that the chests 
are about ten days in cooling down. 

On opening the chests, the bars are found to have suffered a remarkable 
change both in their external appearance and internal structure. They 
are covered with large blisters, obviously produced by some gaseous sub- 
stance raising the softened surface of the metal in its attempt to escape. 
It is conjectured either that the small quantity of sulphur present in the 
bar-iron is converted into bisulphide of carbon during the cementation 
process, and that the vapour of this substance swells the softened metal 
into bubbles as it passes of ; or that the blisters are caused by carbonic 
oxide produced by the action of the carbon upon particles of slag acci- 
dentally present in the bar. On breaking the bars across, the fracture is 
found to have a finely granular structure, instead of the fibrous appearance 
exhibited by bar-iron. Chemical analysis shows that the iron has com- 
bined with about one per cent, of carbon, and the most remarkable part 
of the result is that this carbon is not only found in the external layer of 
iron, which has been in direct contact with the heated charcoal, but is 
also present in the very centre of the bar. It is this transmission of the 
solid carbon through the solid mass of iron which is implied by the term 
cementation. The chemistry of the process probably consists in the forma- 
tion of carbonic oxide from the small quantity of atmospheric oxygen in 
the chest, and the removal of one-half of the carbon from this carbonic 
oxide, by the iron, which it converts into steel, leaving carbonic acid 
(2CO — C — C0 2 ) to be reconverted into carbonic oxide by taking up 
more carbon from the charcoal (C0 2 + C = CO), which it transfers again 
to the iron. Experiment has recently shown that soft iron is capable of 
absorbing, mechanically, 4*15 volumes of carbonic oxide at a low red heat, 
so that the action of the gas upon the metal may occur throughout the 
substance of the bar. The carbonic oxide is retained unaltered by the 
iron, after cooling, unless the bar is raised to the temperature required for 
the production of steel. 

The blistered steel obtained by this process is, as would be expected, 
far from uniform either in composition or in texture ; some portions of 
the bar contain more carbon than others, and the interior contains nume- 
rous cavities. In order to improve its quality, it is subjected to a process 
of fagotting similar to that mentioned in the case of bar-iron ; the bars 
of blistered steel, being cut into short lengths, are made up into bundles, 
which are raised to a welding heat, and placed under a tilt-hammer 
weighing about 2 cwt., which strikes two or three hundred blows in a 
minute ; in this way, the several bars are consolidated into one compound 
bar, which is then extended under the hammer till of the required 
dimensions. The bars, before being hammered, are sprinkled w T ith sand, 
which combines with the oxide of iron upon the surface, and forms 
a vitreous layer which protects the bar from further oxidation. The 
steel which has been thus hammered is much denser and more uniform 
in composition ; its tenacity, malleability, and ductility are greatly in- 
creased, and it is fitted for the manufacture of shears, files, and other 



316 TEMPERING OF STEEL. 

tools. It is commonly known as shear steel. Double shear steel is 
obtained by breaking the tilted bars in two, and welding these into a 
compound bar. 

The best variety of steel, however, which is perfectly homogeneous in com- 
position, is that known as cast steel, to obtain which, about 30 lbs. of blistered 
steel are broken into fragments, and fused in a fire-clay or plumbago cruci- 
ble, heated in a wind-furnace, the surface of the metal being protected from 
oxidation by a little glass melted upon it. The fused steel is cast into 
ingots, several crucibles being emptied simultaneously into the same 
mould. Cast steel is far superior in density and hardness to shear steel, 
but since it is exceedingly brittle at a red heat, great care is necessary in 
forging it. It has been found that the addition, to 100 parts of the cast 
steel, of one part of a mixture of charcoal and oxide of manganese, pro- 
duces a very fine grained steel which admits of being cast on to a bar of 
wrought-iron in the ingot-mould, so that the tenacity of the latter may 
compensate for the brittleness of the steel when the compound bar is 
forged, the wrought-iron forming the back of the implement, and the 
steel its cutting edge. 

This addition of manganese to the cast steel (Heath's patent) has effected 
a great reduction in its cost, allowing the use of blister steel made from 
British bar-iron, whereas, before its introduction, only the expensive iron 
of Swedish or Eussian make could be employed. Only traces of man- 
ganese pass into the steel, the bulk of it going into the slag, and apparently, 
carrying the sulphur and phosphorus with it. 

After the steel has been forged into the shape of any implement, it is 
hardened by being heated to redness, and suddenly chilled in cold water, 
or oil, or mercury. It can thus be rendered nearly as hard as diamond, at 
the same time increasing slightly in volume (sp. gr. of cast steel 7*93 ; after 
hardening, 7*66). The chemical difference between hard and soft steel 
appears to be of the same kind as that between grey and white cast-iron 
(p. 306), the great proportion of the carbon in hard steel being in combina- 
tion with the metal, while in soft steel the greater part seems to be in 
intimate mechanical admixture with the iron, for it is left undissolved on 
treating the steel with an acid. If the hardened steel be heated to red- 
ness, and allowed to cool slowly, it is again converted into soft steel, but 
by heating it to a temperature short of a red heat, its hardness may be 
proportionally reduced. This is taken advantage of in annealing the 
steel or " letting it down " to the proper temper. The very hardest steel 
is almost as brittle as glass, and totally unfit for any ordinary use, but 
by heating it to a given temperature and allowing it to cool, its elasti- 
city may be increased to the desired extent, without reducing its hard- 
ness below that required for the implement in hand. On heating a steel 
blade gradually over a flame, it will acquire a light yellow colour when 
its temperature reaches 430° F., from the formation of a thin film of 
oxide ; as the temperature rises, the thickness of the film increases, and 
at 470° a decided yellow colour is seen, which assumes a brown shade 
at 490°, becomes purple at 520°, and blue at 550°. At a still higher 
temperature the film of oxide becomes so thick as to be black and 
opaque. Steel which has been heated to 430°, and allowed to cool 
slowly, is said to be tempered to the yellow, and is hard enough to take a 
very fine cutting edge, whilst, if tempered to the blue, at 550°, it is too soft 
to take a very keen edge, but has a very high degree of elasticity. The 
following table indicates the tempering heats for various implements : — 



BESSEMER STEEL — SPIEGEL-EISEN. 



317 



Temperiny of Steel. 



Temperature, F. 


Colour. 


Implements thus tempered. 


430° to 450°. 

470°, 

4bU° 

510° 

520° 

530° to 570°. 


Straw-yellow. 

Yellow. 

Brown-yellow. 

Brown-purple. 

Purple. 

Blue. 


Razors, lancets. 

Pen -knives. 

Large shears for cutting metal. 

Clasp -knives. 

Table-knives. 

"Watch-springs, sword-blades. 



If a knife blade be heated to redness, its temper is spoilt, for it is con- 
verted into soft steel. 

In general, the steel implements are ground after being tempered, so 
that they are not seen of the colours mentioned above, except in the case 
of watch-springs. 

A steel blade may be easily distinguished from iron by placing a drop 
of diluted nitric acid upon it, when a dark stain is produced upon the 
steel, from the separation of the carbon. 

Some small instruments, such as keys, gun-locks, &c, which are 
exposed to considerable wear and tear by friction, and require the external 
hardness of steel without its brittleness, are forged from bar-iron, and 
converted externally into steel by the process of case-hardening, which 
consists in heating them in contact with some substance containing 
carbon (such as bone-dust, yellow prussiate of potash, &c), and after- 
wards chilling in water. A process which is the reverse of this is adopted 
in order to increase the tenacity of stirrups, bits, and similar articles 
made of cast-iron; by heating them for some hours, in contact with oxide 
of iron or manganese, their carbon and silicon are removed in the forms 
of carbonic oxide and silicic acid, and they become converted into mal- 
leable cast-iron. 

The opinion that steel owes its properties entirely to the presence of 
carbon is not universally entertained. Some chemists believe that 
nitrogen (or some analogous element) is an indispensable constituent, 
but the proportion of nitrogen found in steel is too minute to warrant 
this supposition. Titanium is alleged by some authorities to have an 
important influence upon the quality of steel, but this also appears to be 
a doubtful matter. Bar-iron may be converted into steel by being kept 
at a high temperature in an atmosphere of coal-gas, from which it 
abstracts carbon. 

Bessemer steel was originally produced by arresting the purification of 
cast-iron in Bessemer's process (page 312), as soon as the carbon had 
diminished to about one per cent., when the steel was poured out in the 
fused state, i.e., in the form of cast steel. A steel of better quality, 
however, has been obtained by continuing the purification until liquid 
bar-iron remains in the converter, and introducing the proper proportion 
of carbon in the form of a peculiar description of white cast-iron known 
as Spiegel-eisen (mirror iron), which crystallises in lustrous tabular crystals, 
and contains large proportions of carbon and manganese, being obtained 
by smelting spathic iron ore rich in manganese, with charcoal as fuel. 



318 EXTRACTION OF WROUGHT IRON FROM THE ORE. 

The Spiegel-eisen is added, in a melted state, to the Bessemer iron before 
pouring from the converter. 

The composition of a sample of Spiegel-eisen smelted from a spathic 
ore, found near Musen in Prussia, is here given : — 

Spiegel-eisen. 

Iron, 82*86 

Manganese, 10 '71 

Silicon, . . 1-00 

Carbon, . 4'32 



Homogeneous iron, as it is called, is really a mild steel containing a 
low percentage of carbon, and obtained by fusing the best Swedish bar- 
iron with carbonaceous matters. It is remarkable for its malleability and 
toughness, and, having undergone complete fusion, it is more likely to be 
homogeneous in composition and structure than wrought-iron produced 
by puddling. 

Paddled steel is obtained by arresting the puddling process at an 
earlier stage than usual, so as to leave a proportion of carbon varying 
from 0*3 to I/O percent. 

Natural steel or German steel results in a similar way, from the incom- 
plete purification of cast-iron in the refinery. The presence of manganese 
in the iron is favourable to its production. 

Krupp's cast steel, manufactured at Essen near Cologne, and employed 
for ordnance, shells, &c, is a puddled steel made from haematite and 
spathic ore, smelted with coke. The iron thus obtained contains much 
manganese, which is removed in the puddling process. Krupp's steel 
contains about 1*2. per cent, of combined carbon, and is fused with a 
little bar-iron for casting ordnance. The fusion is effected in black lead 
crucibles holding 30 lbs. each, of which as many as 1200 are emptied 
simultaneously into the mould for the largest castings. A casting of 16 
tons requires about 400 men, who act together in well-disciplined gangs, 
so that the stream of molten metal shall flow continuously along the gut- 
ters into the mould. Such large castings must be allowed to cool very 
gradually, so that they are kept surrounded with hot cinders, sometimes 
for two or three months, till required for forging. 

217. Direct extraction of wrought-iron from the ore. — Where very rich 
and pure ores of iron, such as haematite and magnetic iron ore, are obtain- 
able, and fuel is abundant, the metal is sometimes extracted without 
being converted into cast-iron. It is probable that the iron of antiquity 
was extracted in this way, for it is doubtful whether cast-iron was known 
to the ancients, and the slag left from old iron-works does not indicate the 
use of any flux. Some works of this description are still in operation in 
the Pyrenees, where the Catalan process is employed. The crucible is 
lined at the sides with thick iron plates, and at the bottom with a refrac- 
tory stone. A quantity of red-hot charcoal is thrown into it, and the 
space above this is temporarily divided into two compartments by a 
shovel. The compartment nearest to the pipe through which the blast 
enters is charged with charcoal, and the other compartment with the 
calcined ore in small pieces. The shovel is then withdrawn, and a 
gradually increasing current of air supplied, fresh ore and fuel being added 



EXTRACTION OF IRON IN THE LABORATORY. 



319 



as they sink down. One part of the oxide of iron is reduced to the 
metallic state by the carbonic oxide, and the rest combines with the silica 
present in the ore to form a slag. After about five hours the spongy 
masses of bar-iron are collected into a ball upon the end of an iron rod, 
and hammered into a compact mass like the metal obtained in the 




Fig. 253. — Catalan forge for smelting iron ores. 



puddliug furnace. The blowing machine employed in the Pyrenees is 
one in which the fall of water from a cistern down a long wooden pipe, 
sucks in, through lateral apertures, a supply of air, which it carries down 
with it into a box, from which the pressure of the column of water 
projects it with some force through the blast-pipe, the water escaping 
from the box through another aperture. 

In the North American bloomery forges a modernised form of the same 
process is adopted. 

The wrought-iron produced by this process always contains a larger 
proportion of carbon than puddled iron, and is therefore somewhat steely 
in character. 

218. Extraction of iron on the small scale. — In the laboratory, iron may be extracted 
from haematite in the following manner : — A fire-clay crucible (A, fig. 254), about 3 
inches high, is filled with damp charcoal powder, rammed down in successive layers ; 
a smooth conical cavity is scooped in the charcoal, and a mixture of 100 grs. 
red haematite, 25 grs. chalk, and 25 grs. pipe-clay, is introduced into it ; the mix- 
ture is covered with a layer of charcoal, and a lid placed on the crucible, which is 
heated in a Sefstrom blast furnace,* fed with coke in small pieces, for about half 

* This very useful furnace, shown in section in fig. 254, consists of two iron cylinders 
with a space (B) between them, into which air is forced through the tube C by a double - 
action bellows. The inner cylinder has a fire-clay lining (D), through which four or six 
copper tubes (E) admit the blast into the fuel. 




320 OXIDES OF IKON. 

an hour. On breaking the cold crucible, a button of cast-iron will be obtained. 

Nearly pure iron may be prepared by fusing the best wire-iron with about one- 
fifth of its weight of pure peroxide of iron, 
to oxidise the carbon and silicon which it 
contains. Some powdered green glass, per- 
fectly free from lead, must be employed as a 
flux, and the crucible (with its cover well 
cemented on with fire-clay) exposed for an hour 
to a very high temperature. A silvery button 
of iron will then be obtained. 

219. — Cliemical properties of iron. 

— In its ordinary condition, iron is 
Fig. 254.— Sefstrom furnace. ™ , -, , % ,, , : r , , . 

° unaffected by perfectly dry air, but in 

the presence of moisture it is gradually converted into nydrated ses- 

quioxide of iron (2Fe 2 3 .3H 2 0), or rust. This conversion takes place 

more rapidly when carbonic acid is present, water being then decomposed, 

and carbonate of iron formed (Fe + H 2 + C0 2 = FeO.C0 2 + H 2 ) • 

this is dissolved by the carbonic acid present, and the solution rapidly 

absorbs oxygen from the air depositing the sesquioxide of iron in a hydrated 

2(FeO.C0 2 ) + = Fe 2 3 + 2C0 2 . 

When iron nails are driven into a new oaken fence, a black streak will 
soon be observed descending from each nail, caused by the formation of 
tannate of iron (ink) by the action of the tannic acid in the wood upon 
the solution of carbonate of iron formed from the nails. The diffusion of 
iron-mould stains through the fibre of wet linen by contact with a nail, is 
also caused by the formation of solution of carbonate of iron. The iron 
in chalybeate waters is also generally present in the form of carbonate 
dissolved in carbonic acid, and hence the rusty deposit which is formed 
when they are exposed to the air. Iron does not rust in water containing 
a free alkali, or alkaline earth, or an alkaline carbonate. 

Concentrated sulphuric and nitric acids do not act upon iron at the 
ordinary temperature, though they dissolve it rapidly when diluted. 
Even when boiling, strong sulphuric acid acts upon it but slowly. 
When iron has been immersed in strong nitric acid (sp. gr. 1*45), it is 
found to be unacted upon when subsequently placed in diluted nitric 
acid, unless previously wiped ; it is then said to have assumed the passive 
state. If iron wire be placed in nitric acid of sp. gr. 1*35, it is acted 
upon immediately, but if a piece of gold or platinum be made to touch it 
beneath the acid, the iron assumes the passive state, and the action ceases 
at once. A state similar to this, the cause of which has not yet been 
satisfactorily explained, is sometimes assumed by other metals, though in 
a less marked degree. 

220. Oxides of iron. — Three compounds of iron with oxygen are known 
in the separate state, and one is believed to exist in certain compounds — 

Protoxide of iron, or ferrous oxide, FeO 

Sesquioxide or peroxide of iron, or ferric oxide, Fe 2 3 

Magnetic oxide, or ferroso-ferric oxide, Fe 3 4 

Ferric acid 0), Fe0 3 

The protoxide of iron is little known in the separate state, on account of 
the readiness with which it absorbs oxygen and forms sesquioxide of iron. 
If a little potash or ammonia be added to a solution of the green sulphate 



FERRIC ACID. 321 

of iron (FeO.SOJ, a whitish precipitate of hydrated protoxide of iron is 
formed, which immediately absorbs oxygen, and is converted into the 
dingy green hydrate of the magnetic oxide ; on exposing this to the air, 
it absorbs more oxygen and becomes brown hydrated peroxide. This 
disposition of the hydrated protoxide to absorb oxygen is turned to 
advantage when a mixture of sulphate of iron with lime or potash is 
employed for converting blue into white indigo. The protoxide of iron 
is a strong base. 

Peroxide or red oxide of iron has been already noticed among the ores 
of iron, and has also been referred to as occurring in commerce under the 
names of colcothar, jeweller's rouge, and Venetian red, which, are obtained 
by the calcination of the green sulphate of iron — 

2(FeO.S0 3 ) = Fe 2 3 + S0 2 + SO s . 

The hydrated peroxide (2Fe 2 3 .3H 2 0), obtained by decomposing a solu- 
tion of perchloride of iron with an alkali, forms a brown gelatinous 
precipitate, which is easily dissolved by acids ; but if it be dried and 
heated to dull redness, it exhibits a sudden glow, and is converted into a 
modification which is dissolved with great difficulty by acids, although 
it has the same composition as the soluble form which has not been 
strongly heated. When the peroxide of iron is heated to whiteness, it 
loses oxygen, and is converted into magnetic oxide of iron, 3Fe 2 3 = 
2Fe 3 4 + 0. Existing as it does in all soils, sesquioxide of iron is 
believed to fulfil the purpose of oxidising the organic matter in the soil, 
and converting its carbon into carbonic acid, to be absorbed by the 
plant ; the sesquioxide being thus reduced to protoxide, which is oxidised 
by the air, and fitted to perform again the same office. The sesquioxide 
of iron, like alumina, is a weak base, and even exhibits some tendency to 
play the part of an acid towards strong bases, though not in so marked a 
degree as alumina. 

Magnetic or black oxide of iron is generally regarded as a compound 
of the protoxide with the sesquioxide of iron (FeO.Fe 2 0,), a view which 
is confirmed by the occurrence of a number of minerals having the same 
crystalline form as the native magnetic oxide of iron, in which the iron, 
or part of it, is displaced by other metals. Thus, spinelle is Mg0.i\l 2 3 ; 
Franklinite, ZnO.Fe.O,, ; chrome-iron ore, FeO.Cr 2 3 . The natural mag- 
netic oxide was mentioned among the ores of iron, and this oxide has 
been seen to be the result of the action of air or steam upon iron at a 
high temperature. The hydrated magnetic oxide of iron (Fe 3 4 .H 2 0) is 
obtained as a black crystalline powder by mixing one equivalent of proto- 
sulphate with one equivalent of persulphate of iron, and pouring the 
mixture into a slight excess of solution of ammonia, which is afterwards 
boiled with it. Magnetic oxide of iron, when acted upon by acids, yields 
mixtures of protosalts and persalts of iron, so that it is not an independent 
basic oxide. 

Ferric acid is only known in combination with bases as ferrates. When iron filings 
are strongly heated with nitre, and the mass treated with a little water, a fine purple 
solution of ferrate of potash is obtained. A better method of preparing this salt 
consists in suspending 1 part of freshly precipitated sesquioxide of iron in 50 parts 
of water, adding 30 parts of solid hydrate of potash, and passing chlorine till a 
slight effervescence commences; Fe 2 O 3 + Cl 6 + 10KEO = 6KCl + 2(K 2 FeO 4 ) + 5H 2 O ; 
the ferrate of potash forms a black precipitate, being insoluble in the strongly alkaline 
solution, though it dissolves in pure water to form a purple solution, which is decom- 
posed even by dilution, oxygen escaping, and hydrated peroxide of iron being pre- 

X 



322 FERRIC CHLORIDE. 

cipitated, 2(K 2 Fe0 4 ) =2K 2 + Fe 2 O 3 + 3 . A similar decomposition takes place on 
boiling a strong solution, or on adding an acid with a view to liberate the ferric 
acid. The ferrates of baryta, strontia, and lime are obtained as fine red precipitates 
when solutions of their salts are mixed with ferrate of potash. 

221. Protosulphate of iron, copperas, green vitriol or ferrous sulphate, 
is easily obtained by heating 1 part of iron wire with 1J parts of strong 
sulphnric acid, mixed with 4 times its weight of water, until the whole of 
the metal is dissolved, when the solution is allowed to crystallise. Its 
manufacture on the large scale by the oxidation of iron pyrites has been 
already referred to. 

It forms fine green rhomboidal crystals, having the composition 
FeO.S0 3 .H 2 0.6Aq. 

The colour of the crystals varies somewhat, from the occasional presence 
of small quantities of the sulphate of sesquioxide of iron (Fe 2 3 . 3S0 3 ). It 
dissolves very easily in twice its weight of cold water, yielding a pale green 
solution. When the commercial sulphate of iron is boiled with water, it 
yields a brown muddy solution, in consequence of the decomposition of the 
sulphate of sesquioxide of iron contained in it, with precipitation of a basic 
sulphate. The sulphate of iron has a great tendency to absorb oxygen, 
and to become converted into the sulphate of sesquioxide. Thus, the 
ordinary crystals when exposed to air gradually become brown, and are 
converted into a mixture of the neutral and basic sulphates of the 
sesquioxide of iron — 

10(FeO.SO 3 ) + 6 = 3(Fe 2 3 .3S0 3 ) + 2Fe 2 3 .S0 3 . 

This disposition to absorb oxygen renders the sulphate of iron useful as a 
reducing agent ; thus, it is employed for precipitating gold in the metallic 
state from its solutions. But its chief use is for the manufacture of ink 
and black dyes, by its action upon vegetable infusions containing tannic 
acid, such as that of nut-galls. This application will be more particularly 
noticed hereafter. 

Sulphate of sesquioxide of iron, or persulphate of iron, ox ferric sulphate, 
is found in Chili as a white silky crystalline mineral, coqidmbite, having 
the composition, Fe 2 3 .3S0 3 .9Aq. 

The phosphates of protoxide and sesquioxide of iron are found associated 
in the mineral known as vivianite or native Prussian blue. 

222. Sesquichloride, or perchloride of iron or ferric chloride (Fe 2 ClJ, 
is obtained in beautiful dark green crystalline scales when iron wire is 
heated in a glass tube through which a current of dry chlorine is passed, 
the sesquichloride passing off in vapour, and condensing in the cool part of 
the tube. The crystals almost instantly become wet when exposed to air, 
on account of their great attraction for water. The perchloride of iron 
may be obtained in solution by dissolving iron in hydrochloric acid, and 
converting the protochloride of iron (FeClJ thus formed into perchloride 
by the action of nitric and hydrochloric acids (p. 172). The solution of 
perchloride of iron has been recommended in some cases as a disinfectant, 
being easily reduced to protochloride, and thus affording chlorine to 
unstable organic matters in contact with it (p. 152). A solution of per- 
chloride of iron in alcohol is used in medicine under the name of tincture 
of iron. 

Solution of perchloride of iron is capable of dissolving a very large quantity of pure 
freshly precipitated peroxide of iron, nine molecules of Fe 2 O s being dissolved by one 
molecule of Fe 2 C] 6 . The solution of oxychloride of iron thus obtained has a very dark 



OXIDES OF MANGANESE. 323 

red colour, and yields, a very copious brown precipitate with common water, or any 
solution containing even a trace of a sulphate. 

223. Equivalent and atomic iveights of iron. — When iron is dissolved 
in hydrochloric acid, 28 parts by weight of iron combine with 1 eq. 
(35*5 parts) of chlorine, displacing 1 part of hydrogen • hence 28 is the 
equivalent weight of iron. 

The specific heat of iron and its isomorphism with magnesium, zinc, and 
cadmium, show that its atomic weight must be represented by double the 
equivalent, or 56, so that iron is a diatomic or bivalent element. 

The molecular formula of ferric chloride has been confirmed by the 
determination of the specific gravity of its vapour, which has been found 
to be 165 times that of hydrogen. If, therefore, one volume (or one 
atom) of hydrogen be represented as having a weight = 1, two volumes 
(or one molecule) of ferric chloride vapour would weigh (165 x 2) 330, 
a number nearly agreeing with the sum of two atoms of iron (112) and six 
atoms of chlorine (21 3 "0); 

It will be remarked that iron possesses a different atomicity accordingly 
as it exists in ferrous or ferric compounds. Thus, in ferrous oxide (FeO) 
and ferrous chloride (FeCl 2 ), it occupies the place of two atoms of hydrogen, 
and is diatomic; but in ferric oxide (Fe 2 3 ) and ferric chloride (Fe 2 Cl 6 ) each 
atom of iron occupies the place of three atoms of hydrogen, and is tri- 
atomic. Some chemists designate the diatomic iron existing in ferrous 
compounds by the name ferrosum (Fe"), and the triatomic iron of the 
ferric compounds by ferricum (Fe'"). 

MANGANESE. 
Mn"=55 parts by weight. 

224. Manganese much resembles iron in several particulars relating both 
to its physical and chemical characters, and is often found in nature, asso- 
ciated, in small quantities, with the compounds of that metal. The metal 
itself has not been applied to any useful purpose. 

It is obtained by reducing carbonate of manganese (MnO.C0 2 ) with 
charcoal, at a very high temperature, when a 'fused mass, composed of 
manganese combined with a little carbon (corresponding to cast-iron), is 
obtained, which is freed from carbon by a second fusion in contact with 
carbonate of manganese. 

Metallic manganese is darker in colour than (wrought) iron, and very 
much harder ; it is brittle, and only feebly attracted by the magnet. It 
is somewhat more easily oxidised than iron. 

225. Oxides of manganese. — Three distinct compounds of manganese 
with oxygen have been obtained in the separate state, and two others are 
believed to exist in combination, bat have not been satisfactorily made 
out in the anhydrous state — 

Protoxide of manganese, MnO 

Sesquioxide „ Mn 2 3 

Binoxide or peroxide of manganese, Mn0 2 
Manganic acid (!) Mn0 3 

Permanganic acid (?) Mn 2 7 . 

The binoxide of manganese is the chief form in which this metal is found 
in nature, and is the source from which all other compounds of manganese 



324 OXIDES OP MANGANESE. 

are obtained. Its chief mineral form is pyrolusite, which forms steel-grey 
prismatic crystals ; but it is also found amorphous, as psilomelane, and in 
the hydrated state as wad. In commerce pyrolusite is known as black 
manganese, or simply manganese, and is largely imported from Germany, 
Spain, &c, for the use of the manufacturer of bleaching-powder, the glass- 
maker, &c. It is also used as a cheap source of oxygen, which it evolves 
when heated to redness, leaving the red oxide of manganese, Mn 3 4 . 
The binoxide of manganese is an indifferent oxide, and does not combine 
with acids ; when heated with strong sulphuric acid, it loses half its 
oxygen, and forms the protoxide of manganese, which is a powerful base, 
and combines with the sulphuric acid to form sulphate of manganese — 

Mn0 2 + H 2 O.S0 3 - MnO.S0 3 + H 2 + . 

Since the natural binoxide contains peroxide of iron, some persulphate of 
iron is formed at the same time ; but if the mixture be dried and heated to 
redness, the iron-salt is decomposed, evolving sulphuric acid, and leaving 
peroxide of iron; while the protoxide of manganese, being a stronger base, 
does not abandon its sulphuric acid ; and the sulphate of manganese may 
be dissolved out of the mass by treatment with water. On evaporating 
the solution, and allowing it to cool, it deposits light pink crystals of sul- 
phate of manganese, MnO.S0 3 .H a 0.4Aq. 

This salt is employed by the dyer and calico-printer in the production 
of black and brown colours. When a solution of sulphate of manganese 
is mixed with solution of chloride of lime (p. 151), it gives a black pre- 
cipitate of hydrated peroxide of manganese — 

2(MnO.S0 3 ) + CaO.CLO +. 2CaO = 2Mn0 2 + 2(CaO.S0 3 ) + CaCl 2 . 

By decomposing a solution of sulphate of manganese with potash or soda, 
a white precipitate of hydrated protoxide of manganese is obtained, which 
becomes brown when exposed to the air, absorbing oxygen, and becoming 
converted into the hydrated sesquioxide of manganese. 

If solution of sulphate of manganese be mixed with carbonate of soda, 
a white precipitate of carbonate of manganese, 2(MnO,C0 2 ).H 2 0, is 
obtained. The pink crystallised mineral manganese spar consists of 
carbonate of manganese (MnO.C0 2 ). 

Protoxide of manganese (MnO) itself is obtained as a green powder 
by heating carbonate of manganese in a tube through which hydrogen is 
passed to exclude the air, which would convert the protoxide into red 
oxide (Mn 3 4 ). The protoxide has been obtained in transparent emerald- 
green crystals. 

Sesquioxide of manganese, crystallised in octahedra, forms the mineral 
braunite, and, in combination with water, the prismatic crystals of man- 
ganite (Mn 2 3 .H 2 0), which often occurs in the commercial ores of man- 
ganese. The sesquioxide is a weak base, dissolving in acids to form deep 
red solutions, which evolve oxygen when heated, leaving salts of the 
protoxide of manganese. The sulphate of sesquioxide of manganese 
combines with sulphate of potash to form manganese-alum K 2 O.S0 3 , 
Mn 2 3 .3S0 3 .24Aq., corresponding in crystalline form, as in composition, 
to alumina-alum. When binoxide of manganese in minute quantity is 
added to melted glass, it imparts a purple colour, which is probably due 
to the formation of a silicate of sesquioxide of manganese. The amethyst 
is believed by some to owe its colour to the same cause. 

Red oxide of manganese (Mn 3 4 ) is the most stable of the oxides 






PEKMANGANATE OF POTASH. 325 

of this metal, and is formed when either of the others is heated in air. 
Thus obtained, it has a brown or reddish colour ; but it is found in 
nature as the black mineral hausmannite. In composition it resembles 
the magnetic oxide of iron, but it seems probable that its true formula is 
2MnO.Mn0 2 , for when treated with diluted nitric acid it leaves the 
black hydrated binoxide. 

"When a compound containing manganese, in however small a quantity, is fused 
on a piece of platinum foil with carbonate of soda (fig. 127), a mass of manganate 
of soda (Ea 2 Mn0 4 ) is formed, which is green while hot, and becomes blue on cooling. 
The oxygen required to convert the lower oxides of manganese into manganic acid 
has been absorbed from the air. 

Manganic acid is obtained in combination with potash, by mixing 
finely powdered binoxide of manganese into a paste with an equal weight 
of hydrate of potash dissolved in a little water, drying the paste, and 
heating it to dull redness in a glass tube, through which oxygen is passed 
as long as it is absorbed. When the mass is treated with a little cold 
water, it gives a dark emerald-green solution, and by evaporating this 
over oil of vitriol, in vacuo, dark-green crystals of manganate of potash 
(K 2 Mn0 4 ) are formed, which have the same crystalline form as those of 
sulphate of potash. These crystals dissolve unchanged in water contain- 
ing potash ; but when dissolved in pure water, they yield a red solution 
of permanganate of potash, and a precipitate of binoxide of manganese — 

3(K 2 O.Mn0 3 ) + 2H 2 = K 2 O.Mn 2 7 + Mn0 2 + 2(K 2 O.H 2 0). 

The change is more completely effected by adding a little free acid, even 
carbonic acid. The changes of colour thus produced have acquired for 
the manganate of potash the name chameleon mineral. The solution of 
manganate of potash (containing free potash) is very easily decomposed 
by substances having an attraction for oxygen. Thus, most organic sub- 
stances abstract oxygen from it, and cause the separation of brown sesqui- 
oxide of manganese ; filtering its solution through paper will even effect 
this change. The offensive emanations from putrefying organic matters 
are at once oxidised and rendered inodorous by manganate of potash or 
soda. 

Manganate of soda (Na 2 Mn0 4 ) obtained by heating binoxide of man- 
ganese with hydrate of soda, under free exposure to air, is employed in a 
state of solution in water, as Coudy's green disinfectant fluid. It is also 
used as a bleaching agent, and in the preparation of oxygen at a cheap 
rate. 

The temporary formation of manganic acid affords a probable explana- 
tion of the effect of binoxide of manganese in facilitating the disengage- 
ment of oxygen from chlorate of potash (p. 31). 

Permanganic acid has been obtained in a hydrated crystalline state by 
decomposing the permanganate of baryta with sulphuric acid, and evapo- 
rating the solution in vacuo. It is a brown substance, easily dissolving 
in water to a red liquid, which is decomposed at about 90° F., evolving 
oxygen, and depositing binoxide of manganese. 

Permanganate of potash, (K 2 O.Mn 2 7 , or KMn0 4 ), is largely used in 
many chemical operations. In order to prepare it, 4 parts of finely 
powdered binoxide of manganese are intimately mixed with 3J parts of 
chlorate of potash, and 5 parts of hydrate of potash dissolved iu a very 
little water. The pasty mass is dried, and heated to dull redness for 
some time in an iron tray or earthen crucible. The oxygen derived from 



326 CHLORIDES OF MANGANESE. 

the chlorate of potash converts the binoxide of manganese into manganic 
acid, which combines with the potash of the hydrate. On treating the 
cold mass with water, the manganate of potash is dissolved, forming a 
dark-green solution. This is diluted with water, and a stream of carbonic 
acid gas passed through it as long as any change of colour is observed ; 
the carbonic acid combines with the excess of potash, the presence of 
which conferred stability upon the manganate, which is then decomposed 
into permanganate of potash and binoxide of manganese. The latter is 
allowed to settle, and the clear red solution poured off and evaporated to 
a small bulk. On cooling, it deposits prismatic crystals of the permanga- 
nate of potash (K 2 O.Mn 2 7 ), which are red by transmitted light, but 
reflect a dark-green colour. The carbonate of potash, being much more 
soluble in water, is left in the solution. Permanganate of potash is 
remarkable for its great colouring power, a very small quantity of the 
salt producing an intense purplish-red colour in a large quantity of water. 
Its solution in water is very easily decomposed by substances having an 
attraction for oxygen, such as sulphurous acid or a ferrous salt, the 
permanganic acid being reduced to protoxide of manganese, so that the 
solution becomes colourless. If a very small piece of iron wire be 
dissolved in diluted sulphuric acid, the solution of ferrous sulphate so 
produced will decolorise a large volume of weak solution of the permanga- 
nate, being converted into ferric sulphate — 

K 2 O.Mn 2 7 + 10(FeO.SO 3 ) 4- 8(H 2 O.S0 3 ) = 
K 2 O.S0 3 + 2(MnO.S0 3 ) + 5(Fe 2 3 .3S0 3 ) + 8H 2 0. 

This decomposition forms the basis of a valuable method for determin- 
ing the proportion of iron in its ores. 

Many organic substances are easily oxidised by permanganate of potash, 
and this is the case especially with the offensive emanations from putres- 
cent organic matter. Hence it is extensively used, under the name of 
Candy's red disinfecting fluid, in cases where a solid or liquid substance 
is to be deodorised. 

226. Chlorides of manganese. — There appear to be three compounds of 
manganese with chlorine, corresponding to three of the oxides, viz., 
MnCl 2 ,Mn 2 Cl 6 and MnCl 4 ; but only the first is obtainable in the pure 
state, the others forming solutions, which are easily decomposed with 
evolution of chlorine. 

The protochloride of manganese (MnCl 2 ) is obtained in large quantity, as a waste 
product in the preparation of chlorine, for the manufacture of bleaching-powder. 
Since there is no useful application for it, the manufacturer sometimes reconverts 
it into the black oxide. As the native binoxide always contains iron, the liquor 
obtained by treating it with hydrochloric acid contains sesquichloride of iron (Fe 2 Cl 6 ) 
mixed with chloride of manganese (MnCl 2 ). In order to separate the iron, advan- 
tage is taken of the circumstance that sesquioxides are weaker bases than the 
protoxides, so that if a small proportion of lime be added to the solution, the iron 

may be precipitated as sesquioxide, without decomposing the chloride of manganese 

Fe 2 Cl 6 + 3CaO = Fe 2 3 + 3CaCl 2 . 

The solution of chloride of manganese is then mixed with chalk, and subjected to 
the action of steam at a pressure of about two atmospheres. Carbonate of manganese 
is precipitated (MnCl 2 + CaO.G0 2 = CaCl 2 +. MnO.C0 2 ), and when this is dried 
and heated to about 600° in a current of moist air, the carbonic acid is expelled, 
and a large proportion of the oxide of manganese is converted into binoxide, which 
may be employed again for the preparation of chlorine. 
According to Weldon's process (page 145), the iron is precipitated as peroxide 



OXIDES OF COBALT. 327 

by adding chalk, which leaves the manganese in solution ; an excess of lime is then 
added and air blown through the mixture at about 150° F., when the white precipi- 
tate of MnO, formed at first, absorbs the oxygen, and becomes a black compound of 
Mn0 2 with lime which is used over again for the preparation of chlorine. Unless 
the lime is added in excess, only MnO.Mn0 2 is formed, so that the excess of lime 
displaces the MnO and allows it to be converted into Mn0 2 . In another process, 
Weld on employs magnesia instead of lime, with the view of afterwards recovering the 
chlorine from the chloride of magnesium, in the form of hydrochloric acid (see 
p. 282), and using the magnesia over again. 

By dissolving permanganate of potash in oil of vitriol, and adding fragments of 
fused chloride of sodium, a remarkable greenish-yellow gas is obtained, which gives 
purple fumes with moist air, and is decomposed by water, yielding a red solution 
which contains hydrochloric and permanganic acids. It, therefore, must contain 
manganese and chlorine, and is sometimes regarded as the perchloride (MnCl 7 ) 
corresponding to permanganic acid ; but it is more probably an oxychloride of man- 
ganese (see Chlorochromic acid). Care is required in its preparation, which is some- 
times attended with explosion. 

COBALT. 

Co" = 59 parts by weight. 

227. Some of the compounds of cobalt are of considerable importance 
in the arts, on account of their "brilliant and permanent colours. It is 
generally found in combination with arsenic and sulphur, forming tin- 
white cobalt, CoAs 2 and cobalt glance, CoAs 2 .CoS 2 , but its ores also gene- 
rally contain nickel, copper, iron, manganese, and bismuth. 

The metal itself is obtained by strongly heating the oxalate of cobalt 
(CoC 2 4 ) in a covered porcelain crucible. In its properties it closely 
resembles iron, but is said to surpass it in tenacity. 

Two oxides of cobalt are known — the protoxide, CoO, which is de- 
cidedly basic, and the sesquioxide, Co 2 3 , which is a very feeble base. 
The protoxide of cobalt, like those of iron and manganese, tends to absorb 
oxygen from the air, and when heated in air, becomes converted into 
CoO.Co. 2 3 , corresponding to the magnetic oxide of iron. The commercial 
oxide of cobalt, which is employed for painting on porcelain, is obtained 
by roasting the ore, in order to expel part of the sulphur and arsenic, 
dissolving it in hydrochloric acid, and precipitating the sesquioxide of iron 
by the careful addition of lime, when the remaining arsenic is also pre- 
cipitated as arseniate of iron. Hydrosulphuric acid is passed through the 
acid solution to precipitate the bismuth and copper, leaving the cobalt 
and nickel in solution. The latter having been boiled to expel the excess 
of hydrosulphuric acid, is neutralised with lime and mixed with solution 
of chloride of lime, which precipitates the sesquioxide of cobalt as a black 
powder, leaving the oxide of nickel in solution, from which it may be pre • 
cipitated by the addition of lime. 

The salts of oxide of cobalt have a fine red colour in the hydrated state, 
or in solution, but are generally blue when anhydrous. The silicate of 
cobalt associated with silicate of potash forms the blue colour known as 
smalt, which is prepared by roasting the cobalt-ore, so as to convert the 
bulk of the cobalt into oxide, leaving, however, a considerable quantity 
of arsenic and sulphur still in the ore. The residue is then fused in a 
crucible with ground quartz and carbonate of potash, when a blue glass 
is formed, containing silicate of cobalt and silicate of potash, whilst the 
iron, nickel, and copper, combined with arsenic and sulphur, collect at 
the bottom of the crucible and form a fused mass of metallic appearance 
known as speiss, which is employed as a source of nickel. The blue glass 



328 COMPOUNDS OF NICKEL. 

is poured into cold water, so that it may be more easily reduced to the 
fine powder in which the smalt is sold. If the cobalt-ore destined for 
smalt be over roasted, so as to convert the iron into oxide, this will pass 
into the smalt as a silicate, injuring its colour. 

Zaffre is prepared by roasting a mixture of cobalt-ore with two or three 
parts of sand. 

ThenanVs blue consists of phosphate of cobalt and phosphate of alumina, 
and is prepared by mixing precipitated alumina with phosphate of cobalt 
and calcining in a covered crucible. The phosphate is obtained by preci- 
pitating a solution of nitrate of cobalt with phosphate of potash or soda. 

RinmarCs green is prepared by calcining the precipitate produced by 
carbonate of soda in a mixture of sulphate of cobalt with sulphate of zinc. 
It is a compound of the oxides of cobalt and zinc. 

Chloride of cobalt (CoCl 2 ), obtained by dissolving oxide of cobalt in 
hydrochloric acid, forms red hyd rated crystals, which become blue when 
their water is expelled. If strong hydrochloric acid be added to a red 
solution of this salt, it becomes blue ; if enough water be now added to 
render it pink, the blue colour may be produced at pleasure by boiling, 
the solution first passing through a neutral tint. Chloride of cobalt is 
employed as a sympathetic ink, for characters written with its pink solu- 
tion are nearly invisible till they are held before the fire, when they 
become blue, and resume their original pink colour if exposed to the air ; 
a little chloride of iron causes a green colour. 

The sulpiride of cobalt (CoS) is obtained as a black precipitate when 
an alkaline sulphide is added to a solution of a salt of cobalt. A sesqui- 
sulphide (Co 2 S 3 ) is found in grey octahedra, cobalt pyrites. The bisul- 
phide (CoS 2 ) has been obtained artificially. 

When ammonia in excess is added to a solution of a salt of cobalt, a 
deep red liquid is produced, which rapidly absorbs oxygen from the air, 
especially if hydrochlorate of ammonia be present, giving rise to the pro- 
duction of some remarkable and complex bases which contain the elements 
of ammonia and of different oxides of cobalt. 

NICKEL. 

Ni" = 59 parts by weight. 

228. Nickel owes its value in the useful arts chiefly to its property of 
imparting a white colour to the alloys of copper and zinc, with which it 
forms the alloy known as German silver. Mckel is very nearly allied to 
cobalt, and generally occurs associated with that metal in its ores. One 
of the principal ores of nickel is the Kupfernickel or copper-nickel, so 
called by the German miners because they frequently mistook it for an 
ore of copper; it has a reddish metallic appearance, and the formula 
MAs. Grey nickel ore or nickel glance is an arseniosulphide of nickel, 
MAs 2 .MS 2 . Arsenical nickel, NiAs 2 corresponds to tin-white cobalt. 
The metal is commonly extracted from the speiss separated during the 
preparation of smalt from cobalt-ores (p. 327) ; the oxide of nickel pre- 
pared by the method described above, when strongly heated in contact 
with charcoal, yields metallic nickel containing carbon. 

The pure metal is obtained by igniting the oxalate, as in the case of 
cobalt, which it much resembles in properties. 

The oxides of nickel correspond in composition to those of cobalt. The 
salts formed by the oxide of nickel (NiO) are usually green, and give 



METALLIC CHROMIUM. 329 

bright green solutions. The hydrated oxide has a characteristic apple- 
green colour, and does not absorb oxygen from the air like the hydrated 
oxide of cobalt. The greater facility with which the latter is converted 
into sesquioxide has been applied (as above described) to effect the separa- 
tion of the two metals. Oxide of nickel has been found native in octa- 
hedral crystals, which have also been obtained accidentally in a copper- 
smelting furnace. 

Sulphate of nickel (MO.S0 3 .H 2 0.6Aq.) forms fine green prismatic 
crystals, the water of constitution in which may be displaced by sulphate 
of potash, forming the double sulphate of nickel and, potash, MO.S0 3 , 
(K 2 O.SO a .6Aq.), which crystallises so readily that it was at one time the 
form in which nickel was separated from the other metals present in 
its ores. 

Three sulphides of nickel are known — a subsulphide, Ni 2 S ; a proio- 
sulphide, NiS, found native as capillary pyrites, and obtained as a black 
precipitate by the action of an alkaline sulphide upon a salt of nickel ; 
and a bisulphide, USTiS^. 

CHEOMIUM. 

Or = 52 '5 parts by weight. 

229. This metal derives its name from xP^ a ; colour, in allusion to the 
varied colours of its compounds, upon which their uses in the arts chiefly 
depend. It is comparatively seldom met with, its principal ore being the 
chrome-iron ore (Fe0.Cr 2 3 ), which is remarkable for its resistance to the 
action of acids and other chemical agents. It is chiefly found in Sweden, 
Bussia, and the United States, and is imported ' for the manufacture of 
bichromate of potash (K 2 0.2Cr0 3 ), which is one of the chief commercial 
compounds of chromium. The ore is first heated to redness and thrown 
into water, in order that it may be easily ground to a fine powder, which 
is mixed with carbonate of potash, chalk being added to prevent the fusion 
of the mass, and strongly heated in a current of air on the hearth of a 
reverberatory furnace, the mass being occasionally stirred to expose a 
fresh surface to the air. The oxide of iron is thus converted into sesqui- 
oxide, and the sesquioxide of chromium (Cr 2 3 ) also absorbs oxygen from 
the air, becoming chromic acid (CrO..), which combines with the potash 
to form chromate of potash (K^O.CrC^). Nitre is sometimes added to 
hasten the oxidation. On treating the mass with water, a yellow solu- 
tion of chromate of potash is obtained, which is drawn off from the 
insoluble residue of sesquioxide of iron and lime, and mixed with a 
slight excess of nitric acid — 

2(K 2 0.Cr0 3 ) + H 2 0.1S T 2 O g = K 2 0.2Cr0 3 + K 2 O.N 2 O g + H 2 . 

Chromate of Bichromate of 

potash. potash. 

The solution, when evaporated, deposits beautiful red tabular crystals of 
bichromate of potash, which dissolve in 10 parts of cold water, forming 
an acid solution. It is from this salt that the other compounds of 
chromium are immediately derived. 

Metallic chromium has received no useful application. It has been 
obtained in octahedral crystals by the action of sodium on sesqui chloride 
of chromium, and in a pulverulent state by the action of potassium. In 
the latter condition it is easily acted on by acids, but the crystallised 
chromium is insoluble even in nitro-hydrochloric acid. Like aluminum, 



330 CHROMATES. 

it is more easily attacked by hydrated alkalies at a high, temperature, 
evolving hydrogen and producing chromates. It is remarkably infusible. 

230. Oxides of Chromium. — Two oxides of chromium are known in 
the separate state — the sesquioxide, Cr 2 3 , and chromic acid, Cr0 3 . Pro- 
toxide of chromium (CrO) is known in the hydrated state, and perchromic 
acid (Cr 2 7 ) is believed to exist in solution. 

Chromic acid, the most important of these, is obtained by adding to 
one measure of a solution of bichromate of potash, saturated at 130° F., 
one measure and a-half of concentrated sulphuric acid, by small portions 
at a time, and allowing the solution to cool, when chromic acid crystallises 
out in fine crimson needles, which are deliquescent, very soluble in water, 
and decomposed by a moderate heat into oxygen and sesquioxide of 
chromium. Chromic acid is a powerful oxidising agent ; most organic 
substances, even paper, will reduce it to the green sesquioxide of chromium. 
A mixture of bichromate of potash and sulphuric acid is employed for 
bleaching some oils, the colouring matter being oxidised at the expense of 
the chromic acid, and sulphate of sesquioxide of chromium produced — 

K 2 0.2Cr0 3 + 4(H 2 O.S0 3 ) = K 2 O.S0 3 + Cr 2 O s .3S0 3 + 3 + 4H 2 0. 

The bichromate itself evolves oxygen when heated to bright redness, being 
first fused, and afterwards decomposed — 

2(K 2 0.2Cr0 3 ) = 2(K 2 O.CrO a ) + Cr a O a + 3 . 

Neutral chromate of potash (K 2 O.Cr0 3 ) is formed by adding carbonate 
of potash to the red solution of bichromate of potash until its red colour 
is changed to a fine yellow, when it is evaporated and allowed to 
crystallise. It forms yellow prismatic crystals having the same form as 
those of sulphate of potash, and is far more soluble in water than the 
bichromate, yielding an alkaline solution. It becomes red when heated, 
and fuses without decomposition. 

Terchromate of potash (K 2 0.3Cr0 3 ) has been obtained in red crystals 
by adding nitric acid to the bichromate. 

Chrome-yellow is the chromate of lead (PbO.Cr0 3 ), prepared by mix- 
ing dilute solutions of acetate of lead and chromate of potash. It is 
largely used in painting and calico-printing, and by the chemist as a 
source of oxygen for the analysis of organic substances, since, when heated, 
it fuses to a brown mass, which evolves oxygen at a red heat. Chrome- 
yellow being a poisonous salt, its occasional use for colouring confectionery 
is very objectionable. Chromate of lead in prismatic crystals forms the 
rather rare red lead ore of Siberia, in which chromium was first discovered. 

Orange chrome is a basic chromate of lead (2PbO.Cr0 3 ), and maybe 
obtained by boiling the yellow chromate with lime — 

2(PbO.Cr0 3 ) + CaO = 2PbO.Cr0 3 + CaO.Cr0 3 . 

The calico-printer dyes the stuff with yellow chromate of lead, and con- 
verts it into orange chromate by a bath of lime-water. 

The colour of the ruby (crystallised alumina) appears to be due to the 
presence of a small proportion of chromic acid. 

Sesquioxide of chromium (Cr 2 3 ) is valuable as a green colour, especially 
for glass and porcelain, since it is not decomposed by heat. It is prepared 
by heating bichromate of potash with one-fourth of its weight of starch, 
the carbon of which deprives the chromic acid of half its oxygen, leaving 



CHLORIDES OF CHEOMIUM. 331 

a mixture of sesquioxide of chromium with carbonate of potash, which may- 
be removed by washing with water. If sulphur be substituted for 
the starch, sulphate of potash will be formed, which may also be 
removed by water. When the sesquioxide of chromium is strongly 
heated, it exhibits a sudden glow, becomes darker in colour, and in- 
soluble in acids which previously dissolved it easily ; in this respect 
it resembles alumina and sesquioxide of iron. Like these oxides, the 
sesquioxide of chromium is a feeble base ; it is remarkable for forming- 
two classes of salts containing the same proportions of acid and base, but 
differing in the colour of their solutions, and in some other properties. 
Thus, there are two modifications of the sulphate of sesquioxide of 
chromium — the green sulphate, Cr 2 3 .3S0 3 .5Aq., and the violet sul- 
phate, Cr 2 3 .3S0 3 .15Aq. The solution of the latter becomes green 
when boiled, being converted into the former. Chrome-alum forms dark 
purple octahedra (K 2 O.S0 3 ,Cr 2 3 .3SO b .24Aq.) which contain the violet 
modification of the sulphate; and if its solution in water be boiled, 
its purple colour changes to green, and the solution refuses to crystallise.* 
The anhydrous sulphate of chromium forms red crystals, which are inso- 
luble in water and acids. A green basic borate of sesquioxide of chromium 
is used in painting and calico-printing, under the name of vert de Guignet, 
and is prepared by strongly heating bichromate of potash with 3 parts of 
crystallised boracic acid, when borate of potash and borate of chromium 
are formed, half the oxygen of the chromic acid being expelled. The borate 
of potash and the excess of boracic acid are afterwards washed out by 
water. By reducing an alkaline chromate with hyposulphite of soda, the 
compound Cr 2 3 .Cr0 3 has been obtained as a brown precipitate. 

Protoxide of chromium (CrO) is not known in the pure state, but is 
precipitated as a brown hydrate when protochloride of chromium is 
decomposed by potash. It 2 bsorbs oxygen even more readily than protoxide 
of iron, becoming converted into a hydrated proto-sesquioxide of chromium 
(CrO.Cr 2 3 ), corresponding in composition to the magnetic oxide of iron. 
The protoxide of chromium is a feeble base ; a double sulphate of protoxide 
of chromium and potash (CrO.S0 3 ,K 2 O.S0 3 .6Aq.) is known, which has the 
same crystalline form as the corresponding ironsalt(FeO.S0 3 ,K 2 O.S0 3 .6Aq.); 
it has a blue colour, and gives a blue solution, which becomes green when 
exposed to air, from the formation of sesquioxide of chromium. 

Per chromic acid (HCr0 4 , or H 2 O.Cr 2 7 ), is believed to exist in the blue 
solution obtained by the action of peroxide of hydrogen upon solution of 
chromic acid, but neither the acid nor its salts have been obtained in a 
separate state. 

231. Chlorides of chromium. — The sesquichloricle of chromium (Cr 2 Cl 6 ), obtained by 
passing dry chlorine over a mixture of sesquioxide of chromium with charcoal, 
heated to redness in a glass tube, is converted into vapour, and condenses upon 
the cooler part of the tube in shining leaflets, having a fine violet colour. Cold 
water does not affect them, but boiling water slowly dissolves them to a green solu- 
tion resembling that obtained by dissolving sesquioxide of chromium in hydrochloric 
acid. 

Protochloride of chromium (CrCl 2 ) results from the action of hydrogen, at a red heat, 
upon the sesquichloride. Strange to say, it is white, and dissolves in water to form 
a blue solution which absorbs oxj^gen from the air, becoming green. It is remark- 
able that if the violet sesquichloride of chromium is suspended in water, and a 
minute quantity of the protochloride added, the sesquichloride immediately dis- 
solves to a green solution, evolving heat. 

Chlorochromic acid (Cr0 2 Cl 2 ) is a very remarkable brown-red liquid, obtained by 
* Exposure to cold, it is said, again converts it into the crystallisable violet form. 



332 GENERAL REVIEW OF THE IRON GROUP. 

distilling 10 parts of common salt and 17 of bichromate of potash, previously fused 
together and broken into fragments, with 40 parts of oil of vitriol — 

K 2 0. 2Cr0 3 + 4NaCl + 3(H 2 O.S0 3 ) = K 2 O.S0 3 + 2(Na 2 0. S0 3 ) + 3H 2 + 2O0 2 Cl 2 . 

It much resembles bromine in appearance, and fumes very strongly in air, the mois- 
ture of which decomposes its red vapour, forming chromic and hydrochloric acids ; 
Cr0 2 Cl 2 + H 2 = Cr0 3 + 2HC1. It is a very powerful oxidising and chlorinating 
agent, and inflames ammonia and alcohol when brought in contact with them. 

It is occasionally used to illustrate the nature of illuminating flames ; for if 
hydrogen be passsd through a bottle containing a few drops of chlorochromic acid, 
the gas becomes charged with its vapour, and, if kindled, burns with a brilliant 
white flame, which deposits a beautiful green film of sesquioxide of chromium upon 
a cold surface. 

The name oxychloride of chromium, applied to this compound, is more correct than 
chlorochromic acid, for it is not known to form salts. "When chlorochromic acid is 
heated, in a sealed tube, to 370° F., it is converted into a black solid body, according 
to the equation 3Cr0 2 Cl 2 = Cl 4 + CrCl 2 .2Cr0 3 .* 

Fluoride of chromium (CrF 6 ) is another volatile compound of chromium, obtained 
by distilling chromate of lead with fiuor spar and sulphuric acid ; it is a red gas, con- 
densible to a red liquid at alow temperature. Water decomposes it, yielding chromic 
and hydrofluoric acids. 

Sesquisulphide of chromium (Cr 2 S 3 ) is formed when vapour of bisulphide of carbon 
is passed over sesquioxide of chromium heated to redness. It forms black lustrous 
scales resembling graphite. 

232. General review of zinc, iron, cobalt, nickel, manganese, and chro- 
mium. — Many points of resemblance will have been noticed in the chemical 
history of these metals to justify their being classed in the same group. 
They are all capable of decomposing water at a red heat, and easily dis- 
place hydrogen from hydrochloric acid. Each of them forms a base by 
combining with one atom of oxygen, and these oxides produce salts which 
have the same crystalline form. All these oxides, except those of zinc 
and nickel, easily absorb oxygen from the air, and are converted into 
sesquioxides. Zinc does not form a sesquioxide, and the sesquioxide of 
nickel is an indifferent oxide, while that of cobalt is very feebly basic ; 
the sesquioxide of manganese is a stronger base, and the basic properties 
of the sesquioxides of chromium and iron are very decided. Zinc and 
nickel do not exhibit any tendency to form a well-marked acid oxide, but 
the existence of an acid oxide of cobalt is suspected ■; and iron, manga- 
nese, and chromium form undoubted acids with three equivalents of 
oxygen. Zinc and nickel are only known to form one compound with 
chlorine ; cobalt and manganese form, in addition to their protochlorides, 
very unstable sesquichlorides known only in solution, but iron and 
chromium form very stable volatile sesquichlorides. The metals com- 
posing this group are all bivalent or diatomic,* and are found associated 
in natural minerals ; this is especially the case with iron, manganese, 
cobalt, and nickel. They are all attracted by the magnet, with the 
exception of zinc, and, with the same exception, require a very high 
temperature for their fusion. Through zinc, the metals of this group are 
connected with magnesium, which resembles it in volatility, in combus- 
tibility, and in the crystalline form of its salts. Iron and chromium con- 
nect this group with aluminum, their sesquioxides being isomorphous with 
alumina, and their sesquichlorides volatile like that of aluminum. 

* Chromium, like iron, is triatomic in the sesquioxides and the compounds derived from 
it, and, in chromic acid, it must be regarded as hexatomic. 



METALLURGY OF COPPER. 333 

COPPER. 

Cu" = 63*5 parts by weight. 

233. Metallic copper is met with in nature more abundantly than 
metallic iron, though the compounds of the latter metal are of more fre- 
quent occurrence than those of the former.* A very important vein of 
metallic copper, of excellent quality, occurs near Lake Superior in North 
America, from which 6000 tons were extracted in 1858. Metallic copper 
is also sometimes found in Cornwall ; and copper sand, containing metallic 
copper and quartz, is imported from Chili. 

234. Ores of copper. — The most important English ore of copper is 
copper pyrites, which is a double sulphide, containing copper, iron, and 
sulphur in the proportions indicated by the formula CuFeS 2 . It may be 
known by its beautiful brass yellow colour and metallic lustre. Copper 
pyrites is found in Cornwall and Devonshire, and is generally associated 
with arsenical pyrites (FeS 2 .EeAs 2 ), tinstone (Sn0 2 ), quartz, fluor spar, 
and clay, A very attractive variety of copper pyrites is called variegated 
copper ore or peacock copper, in allusion to its rainbow colours ; its 
simplest formula is Cu 3 FeS 3 . This variety is found in Cornwall and Kil- 
larney. 

Copper glance (Cu^S) is another Cornish ore of copper, of a dark grey 
colour and feeble metallic lustre. 

Grey copper ore, also abundant in Cornwall, is essentially a compound 
of the sulphides of copper and iron with those of antimony and arsenic, 
but it often contains silver, lead, zinc, and sometimes mercury. 

Malachite, a basic carbonate of copper, is imported from Australia 
(Burra Burra), and is also found abundantly in Siberia. Green malachite, 
the most beautifully veined ornamental variety, has the composition 
CuO.CO,, CuO.H 2 0, and blue malachite is 2(CuO.C0 2 ).CuO.H 2 0. 

Red copper ore (Cu 2 0) is found in West Cornwall, and the black oxide 
(CuO) is abundant in the north of Chili. 

235. The seat of English copper-smelting is at Swansea, which is 
situated in convenient proximity to the anthracite coal employed in the 
furnaces. The chemical process by which copper is extracted from the 
ore includes three distinct operations : — (1), The roasting, to expel the 
arsenic and part of the sulphur, and to convert the sulphide of iron into 
oxide of iron ; (2), the fusion with silica, to remove the oxide of iron as 
silicate, and to obtain the copper in combination with sulphur only ; and 
(3), the roasting of this combination of copper with sulphur, in order to 
expel the latter and obtain metallic copper. 

The details of the smelting process appear somewhat complicated, 
because it is divided into several stages to allow of the introduction of the 
different varieties of ore to be treated. Thus, the first roasting process is 
unnecessary for the oxides and carbonates of copper, and the fusion with 
silica is not needed for those ores which are free from iron, so that they 
may be introduced at a later stage in the operations. 

(1.) Calcining or roasting the ore, to expel arsenic and part of the 

* Copper is not at all frequently found in animals or vegetables ; but Church has made 
the remarkable observation that the red colouring matter (turacine) of the feathers of the 
plantain-eater (touraco) contains as much as 5*9 per cent, of copper. 



334 



WELSH COPPER-SMELTING PROCESS. 



sulphur. — The ores having been sorted, and broken into small pieces, are 
mixed so as to contain from 8 to 10 per cent, of copper, and roasted, in 





Fig. 255. 

quantities of about three tons, for at least twelve hours, on the spacious 
hearth (H, fig. 256) of a reverberatory furnace (fig. 255), at a temperature 
insufficient for fusion, being occasionally stirred to expose them freely to 

the action of the air, which is admitted 
into the furnace through an opening (0) 
in the side of the hearth upon which the 
ore is spread. The oxygen of the air 
converts a part of the sulphur into sul- 
phurous acid gas, and the bulk of the 
arsenic into arsenious acid, which passes 
off in the form of vapour. A part of the 
sulphide of iron is converted into sul- 
phate of iron by absorbing oxygen at an 
early stage of the process, and this sul- 
phate is afterwards decomposed at a 
higher temperature, evolving sulphurous and sulphuric acids, and leaving 
oxide of iron (see p. 322). A portion of the sulphide of copper is also 
converted into oxide of copper during the roasting, so that the roasted ore 
consists essentially of a mixture of oxide and sulphide of copper with 
oxide and sulphide of iron. Since the sulphide of iron is more easily 
oxidised than sulphide of copper, the greater part of the latter remains 
unaltered in the roasted ore. 

During the roasting of copper ore, dense white fumes escape from the 
furnaces. This copper-smoke, as it is termed, contains arsenious, sulphur- 
ous, sulphuric, and hydrofluoric acids, the latter being derived from the 
fluor spar associated with the ore; if allowed to escape, these fumes 
seriously contaminate the air in the neighbourhood, and copper-smelters 
are endeavouring to apply some method of condensing, and perhaps turn- 
ing them to profitable account. 



Fig. 256. 



(2.) Fusion for coarse metal, to remove the oxide of iron by dissolving it 
with silicic acid at a high temperature. — The roasted ore is now mixed 
with metal slag from process 4, and with ores containing silicic acid and 
oxides of copper, but no sulphur; the mixture is introduced into the 
ore-furnace (fig. 257), and fused for five hours at a higher temperature 
than that employed in the previous operation. In this process fluor spar 
is sometimes kidded in order to increase the fluidity of the slag. 



WELSH COPPER-SMELTING PROCESS. 



335 




Fig. 257. 



The oxide of copper acts upon the sulphide of iron still contained in 
the roasted ore, with formation of sulphide of copper nnd oxide of iron ; 
but since there is more sulphide of iron present than the oxide of copper 
can decompose, the excess of sulphide of iron combines with the 
sulphide of copper to form a 
fusible compound, which sepa- 
rates from the slag, and col- 
lects in the form of a matt or 
regulus of coarse metal, in a 
cavity (C) on the hearth of the 
furnace; it is run out into a 
tank of water (T) in order to 
granulate it, so that it may be 
better fitted to undergo the next 
operation. 

The oxide of iron combines 
with the silicic acid contained 
in the charge, to form a fusible 
silicate of iron {ore-furnace 
slag), which is raked out into 
moulds of sand, and cast into 
blocks used for rough building 
purposes in the neighbourhood. 

The composition of the coarse 
metal corresponds pretty closely 
with the formula CuFeS 2 . It 
contains from 33 to 35 per cent, of copper; whilst the original ore, before 
roasting, is usually sorted so that it may contain about 8*5 per cent. 

The ore-furnace slag is approximately represented by the formula 
FeO.Si0 2 ; but it contains a minute proportion of copper, as is shown by 
the green efflorescence on the walls in which it is used around Swansea. 
Fragments of quartz are seen disseminated through this slag. 

(3.) Calcination of the coarse metal, to convert the greater part of the 
sulphide of iron into oxide. — The granulated coarse metal is roasted at a 
moderate heat for twenty-four hours, as in the first operation, so that the 
oxygen of the air may decompose the sulphide of iron, removing the sul- 
phur as sulphurous acid gas, and leaving the iron in the form of oxide. 

(4.) Fusion for 'white metal, to remove the ivlwle of the iron as silicate. 
— The roasted coarse metal is mixed with roaster and refinery slags from 
processes 5 and 6, and with ores containing carbonates and oxides of 
copper, and fused for six hours, as in the second operation. Any sulphide 
of iron which was left unchanged in the roasting, is now converted into 
oxide of iron by the oxide of copper, the latter metal taking the sulphur. 
The whole of the oxide of iron combines with the silicic acid to form a 
fusible slag, the composition of which is approximately represented by the 
formula 3Fe0.2Si0 2 . 

The malt or regulus of white metal which collects beneath the slag is 
nearly pure subsulphide of copper (Cu 2 S), half the sulphur existing in the 
protosulphide (CuS) having been removed by oxidation in the furnace. The 
white metal is run into sand-moulds and cast into ingots. The tin and 
other foreign metals usually collect in the lower part of the ingot, so that, 
for making best selected copper, the upper part is broken off and worked 



336 POLING OF COPPER. 

separately, the inferior copper obtained from the lower part of the ingot 
being termed tile-copper. The ingots of white metal often contain beauti- 
ful tufts of metallic copper in the form of copper moss. 

The slag separated from the white metal (metal-slag) is much more fluid 
than the ore-furnace slag, and contains so much silicate of copper that it 
is preserved for use in the melting for coarse metal. 

(5.) Roasting the white metal, to remove the sulphur and obtain blistered 
copper. — The ingots of white metal (to the amount of about 3 tons) are 
placed upon the hearth of a reverberatory furnace, and heated for four 
hours to a temperature just below fusion, so that they may be oxidised at 
the surface, the sulphur passing off as sulphurous acid, and the copper 
being converted into oxide. During this roasting the greater part of the 
arsenic, generally present in the fine metal, is expelled as arsenious acid. 
The temperature is then raised, so that the charge may be completely 
fused, after which it is lowered again till the 12th hour. The oxide of 
copper now acts upon the sulphide of copper to form metallic copper and 
sulphurous acid gas, which escapes with violent ebullition from the 
melted mass • Cu 2 S + 2CuO = S0 2 + Cu 4 . When this ebullition ceases, 
the temperature is again raised so as to cause the complete separation of 
the copper from the slag, and the metal is run out into moulds of sand. 
Its name of blister copper is derived from the appearance caused by the 
escape of the last portions of sulphurous acid from the metal when solidi- 
fying in the mould. 

The slag (roaster slag) is formed in this operation by the combination 
of a part of the oxide of copper with silicic acid derived from the sand 
adhering to the ingots, and from the hearth of the furnace. The slag 
also contains the silicates of iron and of other metals, such as tin and lead, 
which might have been contained in the white metal. This slag is used 
again in the melting for white metal. • 



(6.) Refining, to remove foreign metals. — This process consists in slowly 
fusing 7 or 8 tons of the blistered copper in a reverberatory furnace, so 
that the air passing through the furnace may remove any remaining sul- 
phur as sulphurous acid, and may oxidise the small quantities of iron, tin, 
lead, &c, present in the' metal. Of course, a large proportion of the 
copper is oxidised at the same time, and the suboxide of copper, together 
with the oxides of the foreign metals, combine with silicic acid (from the 
hearth or from adhering sand) to form a slag which collects upon the sur- 
face of the melted copper. A portion of the suboxide of copper is dis- 
solved by the metallic copper, rendering it brittle or dry copper. 

(J.) Toughening or poling, to remove a part of the oxygen and bring the 
copper to tough-pitch. — After about twenty hours, the slag is skimmed 
from the metal, a quantity of anthracite is thrown over the surface to pre- 
vent further oxidation, and the metal is poled, i.e., stirred with a pole of 
young wood, until a small sample, removed for examination, presents a 
peculiar silky fracture, indicating it to be at loughpitch, when it is cast 
into ingots. 

The chemical change during the poling appears to consist in the re- 
moval of the oxygen contained in the suboxide present in the metal, by 
the reducing action of the combustible gases disengaged from the wood. 
The presence of a small proportion of suboxide of copper is said to confer 
greater toughness upon the metal, so that if the poling be continued until 



EXTRACTION OF COPTER IN THE LABORATORY. 



337 



the whole of the oxygen is removed, overpoled copper of lower tenacity is 
obtained. On the other hand, the brittleness of underpoled copper is due 
to the presence of suboxide of copper in too large proportion. Tough-cake 
copper is that which has been poled to the proper extent. 

When the copper is intended for rolling, a small quantity (not exceed- 
ing J per cent.) of lead is generally added to it before it is ladled into the 
ingot moulds. 

The chemical changes which take place during the above processes will 
be more clearly understood after inspecting the subjoined table, which 
exhibits the composition of the products obtained at different stages of the 
process, these being distinguished by the same numerals as were employed 
in the above description. 

Products obtained in smelting Ores of Copper. 



In 100 parts. 


Ore. 


Roasted 
Ore. 


Coarse 
Metal. 


Roasted 
Coarse 
Metal. 


White 
Metal. 


Blister 
Copper. 


Refined 
Copper. 


Tough- 
pitch 
Copper. 


Copper, .... 

Iron, 

Sulphur, .... 
Oxygen, .... 
Silicic acid, . . . 
Sulphuric acid, 


8-2 
17'9 
19-9 

1-0 
34-3 


(1.) 

8-6 
17'6 
12-5 

4-5 
34-3 

1-1 


(2.) 
33-7 
33-6 
29'2 


(3.) 
33-7 
33-6 
13-0 
11-0 


(4.) 
77-4 
07 
21-0 


(5.) 

98-0 

0-5 

0-2 


(6.) 
99-4 
trace 
trace 
0-4 


(7.) 
99-6 
trace 
trace 
0*03 




Ore 

Furnace 

Slag. 




Metal 
Slag. 


Roaster 
Slag. 


Refinery 
Slag. 




Oxide of iron (FeO), 

Suboxide of copper (Cu 2 0), . . 
Silicic acid, 


(2,) 

28-5 

0-5 

30-0 




(4.) 

56-0 

0-9 

33-8 


(5.) 
28-0 
16-9 

47-5 


(6.) 
3-1 

36-2 
47-4 







Blue metal is the term applied to the regulus of white metal (from process 4), 
when it still contains a considerable proportion of sulphide of iron, in consequence 
of a deficient supply of oxide of copper in the furnace. Pimple metal is obtained in 
the same operation when the oxide of copper is in excess, so that a portion of the 
copper is reduced, as in process 5, with evolution of sulphurous acid, which produces 
the pimply appearance in escaping. The reduced copper gives a reddish colour to 
the pimple copper. Coarse copper is a similar intermediate stage between white 
metal and blistered copper. Tile copper is that extracted from the bottoms of the 
ingots of white metal, when the tops have been detached for making best select 
copper. Piosette or rose copper is obtained by running water upon the toughened 
metal, so as to enable the metal to be removed in films. Anglesea or Mona copper is 
a very tough copper, reduced by metallic iron from the Hue water of the copper 
mines, which contains sulphate of copper. 

236. For the purpose of illustration, copper may be extracted from copper pyrites 
on the small scale in the following manner : — 

200 grains of the powdered ore are mixed with an equal weight of dried borax, 
and fused in a covered earthen crucible (of about 8 oz. capacity), at a full red heat, 
for about half an hour. The earthy matters associated with the ore are dissolved 
by the borax, and the pure copper pyrites collects at the bottom of the crucible. The 
contents of the latter are poured into an iron mould (scorifying mould, fig. 258), 
and when the mass has set, it is dipped into water. The semi- metallic button is 
then easily detached from the slag by a gentle blow ; it is weighed, finely powdered 
in an iron mortar, and introduced into an earthen crucible, which is placed obliquely 
over a dull fire, so that it may not become hot enough to fuse the ore, which should 
be stirred occasionally with an iron rod to promote the oxidation of the sulphur by 
the air. "When the odour of sulphurous acid is no longer perceptible, the crucible is 

Y 




338 IMPURITIES IN COMMERCIAL COPPER. 

placed in a Sefstrom's blast-furnace (fig. 254), and exposed for a few minutes to a white 
heat, in order to decompose the sulphates of iron and copper. When no more fumes of 

sulphuric acid are perceived, the cru- 
cible is lifted from the fire, held over 
the iron mortar, and the roasted ore 
quickly scraped out of it with a steel 
spatula. This mixture of the oxides 
of copper and iron is reduced to a 
fine powder, mixed with 600 grains 
of dried carbonate of soda and 60 
grains of powdered charcoal, re- 
Fig. 258. turned to the same crucible, covered 
with 200 grains of dried borax, 
and heated in a Sefstrom's furnace for twenty minutes. The crucible is then 
allowed to cool partly, plunged into water to render it brittle, and carefully broken 
to extract the button of metallic copper, which is weighed to ascertain the amount 
contained in the original ore. 

237. Effect of impurities upon the quality of copper. — The information 
possessed by chemists upon this subject is still very limited. It has been 
already mentioned that the presence of a small proportion of suboxide of 
copper in commercial copper is found to increase its toughness. It is 
believed that copper, perfectly free from metallic impurities, is not im- 
proved in quality by the presence of the suboxide, but that this substance 
has the effect of counteracting the red-shortness (see p. 313) of commercial 
copper, caused by the presence of foreign metals. 

Sulphur, even in minute proportion, appears seriously to injure the 
malleability of copper. 

Arsenic is almost invariably present in copper, very frequently amount- 
ing to 0*1 per cent., and does not appear to exercise any injurious influence 
in this proportion ; indeed, its presence is sometimes stated to increase 
the malleability and tenacity of the metal. 

Phosphorus is not usually found in the copper of commerce. When 
purposely added in quantity varying from 0*12 to 0*5 per cent, it is found 
to increase the hardness and tenacity of the copper, though rendering it 
somewhat red-short. 

Tin, in minute proportion, is also said to increase the toughness of 
copper, though any considerable proportion renders it brittle. 

Antimony is a very objectionable impurity, and is by no means uncom- 
mon in samples of copper. 

Nickel is believed to injure the quality of copper in which it occurs. 

Bismuth and silver are very generally found in marketable copper, but 
their effect upon its quality has not been clearly determined. 

All impurities appear to affect the malleability and tenacity of copper 
more perceptibly at high than at low temperatures. 

The conducting power of copper for electricity is affected in an ex- 
traordinary degree by the presence of impurities. Thus, if the conducting 
power of chemically pure copper be represented by 100, that of the very 
pure native copper from Lake Superior has been found to be 93, that of 
the copper extracted from the malachite of the Burra Burra mines in 
South Australia was 89, whilst that of Spanish copper, remarkable for 
containing much arsenic, was only 14. 

Pure copper is obtained by decomposing a solution of pure sulphate of 
copper by the galvanic current, as ir the electrotype process. If the 
negative wire be attached to a copper plate immersed in the solution, the 
pure copper may be stripped off this plate in a sheet. 



EFFECT OF SEA-WATER UPON COPPER. 339 

238. Properties of copper. — The most prominent character which 
confers upon copper so high a rank among the useful metals is its mal- 
leability, which allows it to be readily fashioned under the hammer, and 
to be beaten or rolled out into thin sheets ; among the metals in ordinary 
use, only gold and silver exceed copper in malleability, and the com- 
parative scarcity of those metals leads to the application of copper for 
most purposes where great malleability is requisite. 

•Although, in tenacity or strength, copper ranks next to iron, it is still 
very far inferior to it, for a copper wire of -fa inch in diameter will support 
only 385 lbs., while a similar iron wire will carry 705 lbs. without 
breaking ; and in consequence of its inferior tenacity, copper is less ductile 
than iron, and does not admit of being so readily drawn into exceedingly 
thin wires. 

The comparative ease with which copper may be fused, allows it to be 
cast much more readily than iron ; for it will be remembered that the 
latter metal can be liquefied only by the highest attainable furnace heat, 
whereas copper can be fused at about 2000° F., a temperature generally 
spoken of as a bright red heat. 

As being the most sonorous of metals, copper has been, from time 
immemorial, employed in the construction of bells and musical instru- 
ments. The readiness with which it transmits electricity is turned to 
account in telegraphic communication, its conducting power being almost 
equal to that of silver, which is the best of electric conductors. In con- 
ducting power for heat, copper is surpassed only by silver and gold. 

Copper is not so hard as iron, and is somewhat heavier, the specific 
gravity of cast copper being 8*92, and that of hammered or drawn copper 
8-95. 

The resistance of copper to the chemical action of moist air gives it a 
great advantage over iron fer many uses, and the circumstance that it does 
not decompose water in presence of acids, enables it to be employed as 
the negative plate in galvanic couples. 

239. Effect of sea-water upon copper. — When copper is placed in a 
solution of salt in water, no perceptible action takes place ; but in the 
course of time, if the air be allowed access, it becomes covered with a green 
coating of oxy 'chloride of copper (CuCl 2 .3Cu0.4H 2 0), the action probably 
consisting, first, in the conversion of the copper into oxide by the air, 
and afterwards in the decomposition of the oxide by the chloride of 
sodium; 4CuO + 2NaCl - CuCl 2 .3CuO + Na 2 0. The surface of the 
copper is thus corroded, and in the case of a copper-bottomed ship, the 
action of sea-water not only occasions a great waste of copper, but roughens 
the surface of the sheathing, and affords points of attachment to barnacles, 
&c, which injure the speed of the vessel. Many attempts have been made 
to obviate this inconvenience. Zinc has been fastened here and there to 
the outside of the copper, placing the latter in an electronegative con- 
dition ; the copper has been coated with various compositions, but with 
very indifferent success. Muntz metal or yellow sheathing, or malleable 
brass, an alloy of 3 parts of copper and 2 parts of zinc, has been employed 
with some advantage in place of copper, for it is very much cheaper and 
somewhat less easily corroded ; but the difficulty is by no means over- 
come. Copper containing about 0*5 per cent, of phosphorus is said to be 
corroded by sea- water much less easily than pure copper. 

240. Danger attending the use of copper vessels in cooking food.— The 



340 



ALLOYS OF COPPER. 



use of copper for culinary vessels has occasionally led to serious conse- 
quences, from the poisonous nature of its compounds, and from ignorance 
of the conditions under which these compounds are formed. A perfectly 
clean surface of metallic copper is not affected by any of the substances 
employed in the preparation of food, but if the metal has been allowed to 
remain exposed to the action of the air, it becomes covered with a film of 
oxide of copper, and this subsequently combines with water and carbonic 
acid derived from the air, to produce a basic carbonate of copper,* which, 
becoming dissolved, or mixed with the food prepared in these vessels, 
confers upon it a poisonous character. This danger may be avoided by 
the use of vessels which are perfectly clean and bright, but even from 
these, certain articles of food may become contaminated with copper, for 
this metal is much more likely to be oxidised by the air when in con- 
tact with acids (vinegar, juices of fruits, &c), or with fatty matters, or 
even with common salt, and if oxide of copper be once formed, it will be 
readily dissolved by such substances. Hence it is usual to coat the in- 
terior of copper vessels with tin, which is able to resist the action of the 
air, even in the presence of acids and saline matters. 

241. Useful alloys of copper with other metals. — The most important 
alloys of which copper is a predominant constituent are included in the 
following table : — 





Corn/posit 


ion of 100 parts. 








Copper. 


Zinc. 


Tin. 


Iron. 


Nickel. 


Aluminum. 


Brass, 

Muntz metal, .... 
German silver, . . . 
Aich (or Gedge's) metal, 
Sterro-metal, .... 
Bell metal, .... 
Speculum metal, . . 

Bronze 

Gun metal, .... 
Bronze coinage, . . . 
Aluminum bronze, . . 


64 

60 to 70 

51 

60 

55 

78 

66-6 

80 

90-5 

95 

90 


36 

40 to 30 

30-5 

38-2 

42-4 

4 
1 


0'-8 
22 
33-4 
16 

9-5 

4 


1-8 
1-8 


18'5 


10 



Brass is made by melting copper in a crucible, and adding rather more 
than half its weight of zinc. It is difficult to decide whether brass is a 
true chemical compound, or a mere mechanical mixture of copper and 
zinc, because it is capable of dissolving either of those metals when in a 
state of fusion. The circumstance that it can be deposited by decom- 
posing a solution containing copper and zinc by the galvanic current, would 
appear to indicate that it is a chemical compound, and its physical pro- 
perties are not such as would be expected from a mere mixture of its 
constituents. A small quantity of tin is added to brass intended for 
door-plates, which renders the engraving much easier. When it has to 
be turned or filed, about 2 per cent, of lead is usually added to it, in 
order to prevent it from adhering to the tools employed. Brass cannot 
be melted without losing a portion of its zinc in the form of vapour. 
When exposed to frequent vibration (as in the suspending chains of chan- 
deliers) it suffers an alteration in structure and becomes extremely brittle. 

* Often erroneously called verdigris, which is really a basic acetate of copper. 



CUPRIC OXIDE. 341 

The solder used by braziers consists of equal weights of copper and zinc. 
In order to prevent ornamental brass-work from being tarnished by the 
action of air, it is either lacquered or bronzed. Lacquering consists 
simply in varnishing the brass with a solution of shell-lac in spirit, 
coloured with dragon's blood. Bronzing is effected by applying a solution 
of arsenic or mercury, or platinum, to the surface of the brass. By the 
action of arsenious acid dissolved in hydrochloric acid, upon brass, the 
latter acquires a coating composed of arsenic and copper, which imparts a 
bronzed appearance, the zinc being dissolved in place of the arsenic, 
which combines with the copper at the surface — 

As 2 3 + 6HC1 + Zn 3 = As 2 + 3ZnCl 2 + 3H 2 . 

A mixture of corrosive sublimate (bichloride of mercury, HgCl. 2 ) and acetic 
acid is also sometimes employed, when the mercury is displaced by the 
zinc, and precipitated upon the surface of the brass, with which it forms 
a bronze-like amalgam. For bronzing brass instruments, such as theodo- 
lites, levels, &c, a solution of bichloride of platinum is employed, the 
zinc of the brass precipitating a very durable film of metallic platinum 
upon its surface (PtCl 4 + Zn 2 = Pt + 2ZnCl 2 ). Aich-metal is a kind of 
brass containing iron, and has been employed for cannon, on account of 
its great strength. At a red heat it is very malleable. 

Sterro-metal (crreppog, strong) is another variety of brass containing iron 
and tin, said to have been discovered accidentally in making brass with 
the alloy of zinc and iron obtained during the process of making gal- 
vanised iron (p. 292). It possesses great strength and elasticity, and is 
used by engineers for the pumps of hydraulic presses. 

Aluminum bronze has been already noticed, and the alloys of copper 
and tin will be described under the latter metal. 

A very hard white alloy of 77 parts of zinc, 17 of tin, and 6 of copper, 
is sometimes employed for the bearings of the driving-wheels of loco- 
motives. 

Iron and steel are coated with a closely adherent film of copper, by 
placing them in contact with metallic zinc in an alkaline solution of oxide 
of copper, prepared by mixing sulphate of copper with tartrate of potash 
and soda, and caustic soda. The copper is thus precipitated upon the 
iron by slow voltaic action, the zinc being the attacked metal. By 
adding a solution of stannate of soda to the alkaline copper solution, a 
deposit of bronze may be obtained. 

242. Oxides of copper. — Two oxides of copper are well known in the 
separate state, viz., the suboxide Ou 2 0, and the oxide CuO. Another 
oxide, Cu 4 0, has been obtained in a hydrated state, and there is some 
evidence of the existence of an acid oxide. 

The black oxide of copper (cupric oxide), CuO, is the black layer which 
is formed upon the surface of the metal when heated in air. It is employed 
by the chemist in the ultimate analysis of organic substances by com- 
bustion (p. 80), being prepared for this purpose by acting upon copper 
with nitric acid to convert it into nitrate of copper (p. 133), and 
heating this to dull redness in a rough vessel made of sheet copper, when 
it leaves the black oxide ; CuO.N a 5 = 2N0 2 + + CuO. At a higher 
temperature the oxide fuses into a very hard mass; but it cannot be 
decomposed by heat. Oxide of copper absorbs water easily from the air, 
but it is not dissolved by water; acids, however, dissolve it, forming the 



342 SULPHATE OF COPPER. 

salts of copper, whence the use of oil of vitriol and nitric acid for cleans- 
ing the tarnished surface of copper ; a blackened coin, for example, im- 
mersed in strong nitric acid, and thoroughly washed, becomes as bright as 
when freshly coined. Silicic acid dissolves oxide of copper at a high 
temperature, forming silicate of copper, which is taken advantage of in 
producing a fine green colour in glass. 

Red oxide or suboxide of copper (cuprous oxide), Cu 2 0, is formed when 
a mixture of 5 parts of the black oxide with 4 parts of copper filings 
is heated in a closed crucible. It may also be prepared by boiling a solu- 
tion of sulphate of copper with a solution containing sulphite of soda and 
carbonate of soda in equal quantities, when the suboxide of copper is 
precipitated as a reddish yellow powder, which should be washed, by 
decantation, with boiled water — 

2(CuO.SO a ) + 2(Na 2 O.C0 2 ) + Na 2 O.S0 2 = Cu 2 + 3(Na 2 O.S0 3 ) + 2C0,. 

The suboxide of copper is a feeble base, but its salts are not easily 
obtained by direct union with acids, for these generally decompose it into 
metallic copper and oxide of copper, which combines with the acid. In 
the moist state it is slowly oxidised by the air. Ammonia dissolves the 
suboxide, forming a solution which is perfectly colourless until it is 
allowed to come into contact with air, when it assumes a fine blue colour, 
becoming converted into an ammoniacal solution of the oxide. If the 
blue solution be placed in a stoppered bottle (quite filled with it) with a 
strip of clean copper, it will gradually become colourless, the oxide being 
again reduced to suboxide, a portion of the copper being dissolved. When 
copper filings are shaken with ammonia in a bottle of air, the same blue 
solution is obtained, the oxidation of the copper being attended with a 
simultaneous oxidation of a portion of the ammonia, and its conversion 
into nitrous acid, so that white fumes of nitrite of ammonia are formed 
in the upper part of the bottle. If the blue solution be poured into a 
large quantity of water, a light blue precipitate of hydrated oxide of 
copper is obtained. The ammoniacal solution of oxide of copper has the 
unusual property of dissolving paper, cotton, tow, and other varieties of 
cellulose, this substance being reprecipitated from the solution on adding 
an acid. 

Suboxide of copper, added to glass, imparts to it a fine red colour, 
which is turned to account by the glass-maker. 

Quadrant- oxide of copp>er, Cu 4 0, has been obtained in combination 
with water, by the action of protochloride of tin and potash upon a salt of 
copper. 

Cupric acid is believed to be formed when metallic copper is fused with 
nitre and caustic potash. The mass yields a blue solution in water, which 
is very easily decomposed, with evolution of oxygen and precipitation of 
oxide of copper. The existence of an unstable oxide of copper, containing 
more than one atom of oxygen, is also rendered probable by the cir- 
cumstance, that oxide of copper acts like binoxide of manganese in facili- 
tating the disengagement of oxygen from chlorate of potash by heat 
(page 31). 

243. Sulphate of copper. — The beautiful prismatic crystals known as 
blue vitriol, blue stone, blue copperas, or sulphate of copper, have been 
already mentioned as formed in the preparation of sulphurous acid (p. 199), 
by dissolving copper in oil of vitriol, a process which is occasionally 



SULPHATE OF COPPER. 343 

employed for the manufacture of this salt. A considerable supply of the 
sulphate is obtained as a secondary product in the process of silver- 
refining (p. 210). 

The sulphate of copper is also manufactured by roasting copper pyrites 
(FeCuS 2 ) with free access of air, when it becomes partly converted into a 
mixture of sulphate of copper with sulphate of iron, FeCuS 2 + 8 = 
FeO.S0 3 + CuO.S0 3 . 

The sulphate of iron, however, is decomposed by the heat, losing its 
sulphuric acid, and leaving simply peroxide of iron (see p. 321). "When 
the roasted mass is treated with water, the oxide of iron is left undis- 
solved, but the sulphate of copper enters into solution, and may be 
obtained in crystals by evaporation. 

These crystals, as they are found in commerce, are usually opaque, 
but if they are dissolved in hot water and allowed to crystallise slowly, 
they become perfectly transparent, and have then the composition 
expressed by the formula Cu0.S0 3 .5H 2 0. If the crystals be heated to 
the temperature of boiling water, they lose four-fifths of their water, and 
crumble down to a greyish white powder, which has the composition 
CuO.S0 3 .H 2 0, and if this be moistened with water, it becomes very 
hot and resumes its original blue colour. The whitish opacity of the 
ordinary crystals of blue stone is due to the absence of a portion of the 
water of crystallisation. 

The fifth molecule of water can be expelled only at a temperature 
of nearly 400° F., and is therefore generally called water of consti- 
tution (see p. 41), the formula of the crystals being then written 
CuO.SCLH 2 0.4Aq. The crystals dissolve in four parts of cold and two 
parts of boiling water. The solution reddens litmus. 

The sulphate of copper is largely employed by the dyer and calico- 
printer, and in the manufacture of pigments. It is also occasionally used 
in medicine, in the electrotype process, and in galvanic batteries. 

If a solution of sulphate of copper be mixed with an excess of solution 
of potash, a blue precipitate of hydrated oxide of copper (CuO.H 2 0) is 
produced. On boiling this in the liquid, it loses its water and becomes 
black oxide. The paint known as blue verditer is hydrated oxide of 
copper obtained by decomposing nitrate of 'copper with hydrate of 
lime. 

When ammonia is added to solution of sulphate of copper, a basic 
sulphate is first precipitated, which is dissolved by an excess of ammonia 
to a dark blue fluid. On allowing this to evaporate, dark blue crystals of 
ammonio-sulpliate of copper, CuO.S0 3 , 4NH 3 , H 2 0, are deposited. They 
lose their ammonia when exposed to the air. 

A basic sulphate of copper, CuO.S0 3 , 4(CuO.H 2 0), constitutes the 
mineral brochantite. 

Sulphate of copper cannot easily be separated by crystallisation from 
the sulphates of iron, zinc, and magnesia, because it forms double salts 
with them, which contain, like those sulphates, 7 molecules of water. 
An instance of this is seen in the black vitriol obtained from the mother- 
liquor of the sulphate of copper at Mansfeld, and forming bluish black 
crystals isomorphous with green vitriol, FeO.S0 3 ,7H 2 0. The formula of 
black vitriol may be written, (CuMgFeMnCoM) O.S0 3 .7H 2 0, the six 
isomorphous metals being interchangeable without altering the general 
character of the salt. 

Arsenite of copper or Scheele's green has been mentioned at p. 244. 



344 CUPltOUS CHLORIDE. 

The basic phosphates of copper compose the minerals tagalite and 
Ubethenite. 

The basic carbonates of copper have been noticed as forming the very 
beautiful minerals blue malachite, or chessylite, and green malachite. 

Mineral green (CuO.C0 2 , CuO.H 2 0) has the same composition as 
green malachite, and is prepared by mixing hot solutions of carbonate of 
soda and sulphate of copper. When boiled in the liquid, it is gradually 
converted into black oxide of copper. 

Silicates of copper are found in the minerals dioptase, or emerald copper, 
and chrysocolla. 

244. Chlorides of copper. — The chloride of copper (cupric chloride) 
(CuCl 2 ) is produced by the direct union of its elements, when it forms a 
brown mass, which fuses easily, and is decomposed into chlorine and sub- 
chloride of copper, the latter being afterwards converted into vapour. 
When dissolved in water, it gives a solution which is green when concen- 
trated, and becomes blue on dilution. The hydrated chloride of copper 
is readily prepared by dissolving the black oxide in hot hydrochloric 
acid, and allowing the solution to crystallise ; it forms green needle-like 
crystals (CuCl 2 .2H 2 0). A solution of chloride of copper in alcohol burns 
with a splendid green flame, and the chloride imparts a similar colour to 
a gas flame. 

Oxy chloride of copper (CuCl 2 .3Cu0.4H 2 0) is found at Atacama, in 
prismatic crystals, and is called atacamite. The paint Brunsivick green 
has the same composition, and is made by moistening copper with solu- 
tion of hydrochloric acid or of sal-ammoniac, and exposing it to the air in 
order that it may absorb oxygen — 

Cu 4 + 2HC1 + 3H 2 + 4 = CuCl 2 .3Cu0.4H 2 0. 

The Brunswick green of the shops frequently consists of a mixture of 
Prussian blue, chromate of lead, and sulphate of baryta. 

Subchloride of copper {cuprous chloride), Cu 2 Cl 2 , is formed when fine 
copper turnings are shaken with strong hydrochloric acid in a bottle of 
air (Cu.j + 2HC1 + = Cu 2 Cl 2 + H 2 0). The subchloride dissolves in 
the excess of hydrochloric • acid, forming a brown solution, from which 
water precipitates the white subchloride of copper, for this is one of the 
few chlorides insoluble in water. When exposed to light, it assumes a 
purplish grey tint. It may be obtained in larger quantity by dissolving 
5 parts of black oxide of copper in hydrochloric acid, and boiling with. 
4 parts of fine copper turnings, the brown solution being afterwards pre- 
cipitated by water. If the solution be moderately diluted and set aside, it 
deposits tetrahedral crystals of the subchloride. Ammonia (free from air) 
dissolves the subchloride to a colourless liquid, which becomes dark-blue 
by contact with air, absorbing oxygen. The ammoniacal solution of sub- 
chloride of copper is employed as a test for acetylene (p. 89), which gives 
a red precipitate with it. The solution may be preserved in a colourless 
state by keeping it in a well-stoppered bottle, quite full, with strips of 
clean copper. When copper, in a finely divided state, is boiled with 
solution of hydrochlorate of ammonia, the solution deposits colour- 
less crystals of the salt Cu 2 Cl 2 (NH 3 ) 2 . If the solution of this salt be 
exposed to the air, blue crystals are deposited, having the formula 
Cu 2 Cl 2 . (NH. < ) 2 ,CuCl 2 .(NH 3 ).^H 2 0, and on further exposure, a compound 
of this last salt with hydrochlorate of ammonia is deposited. The solu- 



COrPER AND SULPHUR. 345 

tion of subchloride of copper in hydrochloric acid is employed for 
absorbing carbonic oxide in the analysis of gaseous mixtures (p. 251). 
When this solution is exposed to air it absorbs oxygen, and deposits the 
oxy chloride of copper. A strong solution of hydrochlorate of ammonia 
or of chloride of potassium readily dissolves the cuprous chloride, even 
in the cold, forming soluble double chlorides. The solution in chloride 
of potassium does not absorb oxygen quite so easily as that in hydro- 
chlorate of ammonia. 

245. Sulphides of copper. — Copper has a very marked attraction for 
sulphur, even at the ordinary temperature. A bright surface of copper 
soon becomes tarnished by contact with sulphur, and hydrosulphuric acid 
blackens the metal. Finely divided copper and sulphur combine slowly 
at the ordinary temperature, and when heated together, they combine with 
combustion. A thick copper wire burns easily in vapour of sulphur 
(p. 193). Copper is even partly converted into sulphide when boiled 
with sulphuric acid, as in the preparation of sulphurous acid gas. This 
great attraction of copper for sulphur is taken advantage of in the process 
of kernel-roasting for extracting the copper from pyrites containing as 
little as 1 per cent, of the metal. The pyrites is roasted in large heaps 
(p. 190) for several weeks, when a great part of the iron is converted 
into peroxide, and the copper remains combined with sulphur, forming 
a hard kernel in the centre of the lumps of ore. This kernel contains 
about 5 per cent, of copper, and can be smelted with economy. Children 
are employed to detach the kernel from the shell, which consists of 
peroxide of iron and a little sulphate of copper, which is washed out 
with water. 

The subsuljjliide of copper (Cu 2 S) has been mentioned among the ores 
of copper, and among the furnace products in smelting, when it is some- 
times obtained in octahedral crystals. It is not attacked by hydrochloric 
acid, but nitric acid dissolves it readily. Copjper pyrites is believed to 
contain the copper in the form of subsulphide, its true formula being 
Cu 2 S.Fe.,S 3 ; for if the copper be present as sulphide, CuS, the iron must 
be present as protosulphide, and the mineral would have the formula 
CuS.FeS. Now, FeS is easily attacked by dilute sulphuric or hydro- 
chloric acid, which is not the case with copper pyrites. Nitric acid, how- 
ever, attacks it violently. 

Sulphide of copper (CuS) occurs in nature as indigo copper or blue 
copper, and may be obtained as a black precipitate by the action of 
hydrosulphuric acid upon solution of sulphate of copper. When this 
precipitate is boiled with sulphur and hydrosulphate of ammonia, it is 
dissolved in small quantity, and the solution on cooling deposits fine 
scarlet needles containing a higher sulphide of copper combined with 
hydrosulphate of ammonia. 

A pentasulphide of copper (CuS 5 ) is obtained by decomposing sulphate 
of copper with pentasulphide of potassium ; it forms a black precipitate, 
distinguished from the other sulphides of copper by its solubility in car- 
bonate of potash. 

The sulphides of copper, when exposed to air in the presence of water, 
are slowly oxidised and converted into sulphate of copper, which is dis- 
solved by the water. It appears to be in this way that the blue ivater of 
the copper mines is formed. 

Phosphide of coppor (Cu 3 P 2 ), obtained as a black powder by boiling 



346 CHARACTERS OF LEAD. 

solution of sulphate of copper with phosphorus, has been already men- 
tioned as a convenient source of phosphuretted hydrogen. Another phos- 
phide, obtained by passing vapour of phosphorus over finely divided 
copper at a high temperature, is employed in Abel's composition for 
magneto-electric fuzes, in conjunction with subsulphide of copper and 
chlorate of potash. 

Silicon may be made to unite with copper by strongly heating finely 
divided copper with silicic acid and charcoal. A bronze-like mass is thus 
obtained, containing about 5 per cent, of silicon. It is said to rival iron 
in ductility and tenacity, and fuses at about the same temperature as 
bronze. 

LEAD. 

Pb" = 207 parts by weight. 

246. Lead owes its usefulness in the metallic state chiefly to its soft- 
ness and fusibility. The former quality allows it to be easily rolled into 
thin sheets, and to be drawn into the form of tubes or pipes ; it is indeed 
the softest of the metals in common use, and, at the same time, the least 
tenacious, so that it can only be draw T n with difficulty into thin wire, and 
is then very easily broken. The ease with which it makes a dark streak 
upon paper shows how readily minute particles of the metal may be 
abraded. Its want of elasticity also recommends it for some special uses, 
as for deadening a shock or preventing a rebound. 

In fusibility it surpasses all the other metals commonly employed in 
the metallic state, except tin, for it melts at 617° F., and this circum- 
stance, taken in conjunction with its high specific gravity (1 1 # 4), parti- 
cularly adapts it for the manufacture of shot and bullets. For one of its 
extensive uses, however, as a covering for roofs, it would be better suited 
if it were lighter and less fusible, for in case of fire in houses so roofed, 
the fall of the molten lead frequently aggravates the calamity. 

With the exception, perhaps, of the ores of iron, none is more abun- 
dant in this country thau the chief ore of lead, galena, a sulphide of lead 
(PbS). This ore might at the first glance be mistaken for the metal 
itself, from its high specific gravity and metallic lustre. It is found 
forming extensive veins in Cumberland, Derbyshire, and Cornwall, 
traversing a limestone rock in the two first counties, and a clay slate in 
the last. Spain also furnishes large supplies of this important ore. 

Galena presents a beautiful crystalline appearance, being often found . 
in large isolated cubes, which readily cleave or split up in directions 
parallel to their faces. Blende (sulphide of zinc) and copper pyrites 
(sulphide of copper and iron) are frequently found in the same vein with 
galena, and it is usually associated with quartz (silica), heavy-spar (sul- 
phate of baryta), or fluor spar (fluoride of calcium). Considerable 
quantities of sulphide of silver are often present in galena, and in many 
specimens the sulphides of bismuth and antimony are found. 

Though the sulphide is the most abundant natural combination of lead, 
it is by no means the only form in which this metal is found. The 
metal itself is occasionally met with, though in very small quantity, 
and the carbonate of lead (PbO.C0. 2 ), white lead ore, forms an important 
ore in the United States and in Spain. The sulphate of lead (PbO.S0 3 ) 
is also found in Australia, and is largely imported into this country to 
be smelted. 



SMELTING OF GALENA. 



347 



247. The extraction of lead from galena is effected by taking advan- 
tage of the circumstance, that when a combination of a metal with oxy- 
gen is raised to a high temperature in contact with a sulphide of the same 
metal, the oxygen and sulphur unite, and the metal is liberated. 

The ore, having been separated by mechanical treatment as far as possi- 
ble from the foreign matters associated with it, is mixed with a small 
proportion of lime, and spread over the hearth of a reverberatory furnace 
(fig. 259), the sides of which are considerably inclined towards the 
centre, so as to form a hollow for the reception of the molten lead. 

During the first stage of the smelting process, the object is to roast 
the ore with free access of air, exposing as large a surface as possible, 




Fig. 259. — Furnace for smelting lead-ores. 



on which account the heat is kept below that at which galena fuses ; 
indeed, during the first two hours, no fuel is thrown into the grate, 
sufficient heat being radiated from the sides of the furnace, which have 
become red hot during the smelting of the previous charge of ore. The 
ore is stirred from time to time, to expose fresh surfaces to the action of 
the atmospheric oxygen. 

The effect of this roasting is to convert a portion of the sulphide of lead 
(PbS) into sulphate of lead (PbO.S0 3 ), whilst another portion loses its 
sulphur, which is evolved as sulphurous acid (S0 2 ), and acquires oxygen 
in its stead, becoming converted into oxide of lead (PbO). A large 
proportion of the galena, however, remains unoxidised. "When the roast- 
ing is sufficiently advanced, some fuel is thrown into the grate, some rich 
slags from previous smeltings are thrown on to the hearth, the damper is 
slightly raised, and the doors of the furnace are closed, so that the charge 
may be heated to the temperature at which the oxide and sulphate of 
lead act upon the unaltered sulphide, furnishing metallic lead, whilst the 
sulphur is expelled in the form of sulphurous acid : 

PbS + 2PbO = Pb 3 + S0 2 , and PbO.S0 3 + PbS = Pb 2 + 2S0 2 . 

During this part of the operation, the contents of the hearth are 
constantly raked up towards the fire-bridge, so as to facilitate the 
separation of the lead, and to cause it to run down into the hollow 
provided for its reception. It is also found that the separation of the 
lead from the slags is much assisted by occasionally throwing open the 
doors to chill the furnace. After about four hours, the charge is reduced 
to a pretty fluid condition, the lead having accumulated at the bottom 



348 



SMELTING OF GALENA. 



of the depressed portion of the hearth with the slag above it ; this slag- 
consists chiefly of the silicates of lime and oxide of lead, and would have 
contained a larger proportion of the latter, if the lime had not been 
added as a flux at the commencement of the operation. In order still 
further to reduce the quantity of lead in the slag, a few more shovelfuls 
of lime are now thrown into the hearth, together with a little small coal, 
the latter serving to reduce to the metallic state the oxide of lead dis- 
placed by the lime from its combination with the silicic acid. 

But since silicate of lime is far less fusible than silicate of oxide of 
lead, the effect of this addition of lime is to " dry up " the slags to a 
semi-solid mass, and it will now be seen that if the whole of the 
lime had been added at the commencement of the smelting, the 
diminished fusibility of the slag would have opposed an obstacle to the 
separation of the metallic lead. 

During the last hour or so, the temperature is very considerably raised, 
and at the expiration of about six hours, when the greater portion of 
the lead is thought to have separated, the slag is raked out through 
one of the doors of the furnace, and the melted metal allowed to run 
out through a tap-hole in front of the lowest portion of the hearth, 
into an iron basin, from which it is ladled into pig-moulds. 

The rich slags, together with the layer of subsulphide of lead (Pb 2 S) 
which forms over the surface of the metal, are worked up again with a 
fresh charge of ore. 

In the smelting of galena, a very considerable quantity of lead is car- 
ried off in the form of vapour ; and in order to condense this, the gases 
from the furnace are made to pass through flues, the aggregate length of 
which is sometimes three or four miles, before being allowed to escape- 
up the chimney. When these flues are 
swept, many tons of lead are recovered 
in the forms of oxide and sulphide. 

In the north of England, the smelt- 
ing of lead ores is now generally con- 
ducted in an economico-furnace (fig. 
260), or small blast-furnace, instead of 
in the reverberatory furnace described 
above. Air is supplied to the furnace 
through three blast-pipes (A), and the 
lead-ore and fuel being charged in at B, 
the lead runs into a cavity (C) at the. 
bottom of the furnace, whilst the slag- 
flows over into a reservoir (D) outside 
the furnace. The charge is sprinkled 
with water through the rose (E) fixed 
just above the opening into the chim- 
ney (F), to prevent it from being blown 
away by the current of air. 

248. Some varieties of lead, particu- 
larly those smelted from Spanish ores, 
are known as hard lead, their hardness 
being chiefly due to the presence of 
antimony, and since this hardness interferes materially with some of the 
uses of the metal, such lead is generally subjected to an improving or ml- 




EXTRACTION OF SILVER FROM LEAD. 



349 




Fisc. 261. 



cining process, in which the impurities are oxidised and removed, together 
with a portion of the lead, in the dross.* To effect this, six or eight tons 
of the hard lead are fused in an iron pot (P, fig. 261), and transferred to 
a shallow cast-iron pan 
(C) measuring about ten 
feet by five. In this 
pan, which is set in 
the hearth of a rever- 
beratory furnace, and is 
about eight inches deep 
nearest the grate, and 
nine inches at the other 
end, the lead is kept in 
fusion by the flame which 
traverses it from the 
grate G to the flue P, 
for a period varying with 
the degree of impurity, 
some specimens being 
found sufficiently soft 
after a single day's cal- 
cination, whilst others 
must be kept in a state 

of fusion for three or four weeks. The workman judges of the progress 
of the operation by a peculiar flaky crystalline appearance assumed by a 
small sample on cooling. When sufficiently purified, the metal is run 
off and cast into pigs. 

At first sight, it is not intelligible how antimony should be removed 
from lead by calcination, since lead is the more easily oxidised metal. 
The result must be ascribed to the tendency of antimony to form anti- 
monic acid (Sb 2 5 ) which combines with the oxide of lead. The dross 
(antimoniate of lead) formed in this process, when reduced to the metallic 
state, yields an alloy of lead with 30 or 40 per cent, of antimony, which 
is much used for casting type furniture for printers. 

249. Extraction of silver from lead. — The lead extracted from galena 
often contains a sufficient quantity of silver to allow of its being profitably 
extracted. Previously to the year 1829, this was practicable only when 
the lead contained more than 1 1 oz. of silver per ton, for the only process 
then known for effecting the separation of the two metals was that of 
cupellation, which necessitates the conversion of the whole of the lead into 
oxide, which has then to be separated from the silver and again reduced 

* The following analyses illustrate the composition of hard lead : — 





English. 


Spanish. 


Lead, .... 

Antimony, 

Copper, .... 

Iron, .... 


99-27 
0-57 

o-i 

0-04 
100-00 


95-81 
3-66 
0-32 
0-21 

100-00 



350 



PATTINSON S DESILVEEISING PROCESS. 



to the metallic state, thus consuming so large an amount of labour, that a 
considerable yield of silver must be obtained to pay for it. 

By the simple and ingenious operation known as Pattinsorts desilver- 
ising process, a very large amount of the lead can be at once separated in 
the metallic state with little expenditure of labour, thus leaving the re- 
mainder sufficiently rich in the more precious metal te defray the cost of 
the far more expensive process of cupellation, so that 3 or 4 oz. of silver 
per ton can be extracted with profit. Pattinson founded his process upon 
the observation that when lead containing a small proportion of silver is 
melted and allowed to cool, being constantly stirred, a considerable quan- 
tity of the lead separates in the form of crystals containing a very minute 
proportion of silver, almost the whole of this metal being left behind in 
the portion still remaining liquid. 

Eight or ten cast-iron pots, set in brickwork, each capable of holding 
about 6 tons of lead, are placed in a row, with a fire-place underneath each 
of them (fig. 262). Suppose that there are ten pots numbered consecu- 




Fig. 262. — Pattinson's desilverising process. 



tively, that on the extreme left of the workman being No. 1, and that on 
his extreme right No. 10. About 6 tons of the lead containing silver are 
melted in pot No. 5, the metal skimmed, and the fire raked out from 
beneath so that the pot may gradually cool, its liquid contents being con- 
stantly agitated with a long iron stirrer. As the crystals of lead form, 
they are well drained in a perforated ladle (about 10 inches wide and 5 
inches deep) and transferred to pot No. 4. When about fths of the 
metal have thus been removed in the crystals, the portion still remaining 
liquid, which retains the silver, is ladled into pot No. 6, and the pot 



CUPELLATION OF ARGENTIFEROUS LEAD. 



35] 



No. 5, which is now empty, is charged with fresh argentiferous lead to be 
treated in the same manner. 

When pots Nos. 4 and 6 have received, respectively, a sufficient quantity 
of the crystals of lead and of the liquid part rich in silver, their contents 
are subjected to a perfectly similar process, the crystals of lead being 
always passed to the left, and the rich argentiferous alloy to the right. 
As the final result of these operations, the pot No. 10, to the extreme 
right, becomes filled with a rich alloy of lead and silver, sometimes con- 
taining 300 ounces of silver to the ton, whilst pot No. 1, to the extreme 
left, contains lead in which there 
is not more than ^ ounce of silver 
to the ton. This lead is cast into 
pigs for the market. The ladle 
used in the above operation is 
kept hot by a small temper pot 
containing melted lead. A ful- 
crum is provided at the edge of 
each pot, for resting the ladle 
during the shaking of the crystals 
to drain off the liquid metal. 
Any copper present in the lead 
is also left with the silver in the 
liquid portion. 

250. In order to extract the 
silver from the rich alloy, it is 
subjected to a process of refining, 
or cupellation, which is founded 
upon the oxidation suffered by 
lead when heated in air, and upon 
the absence of any tendency on 
the part of silver to combine 
directly with oxygen. 

The refinery or cupelling fur- 
nace (fig. 263), in which this 

operation is performed, is a reverberatory furnace, the hearth of which con- 
sists of a cupel (0), made by ramming moist powdered bone-ash mixed 
with a little wood-ash into an oval iron frame about 4 inches deep, and pro- 
vided with four cross-bars at the bottom, each about 4 inches wide. When 
this frame has been well filled with bone-ash, part of it is scooped out, so 
as to leave the sides about two inches thick at the top, aud three inches 
at the bottom, the bone-ash being left about one inch thick above the 
iron cross-bars. 

The cupel, which is about 4 feet long by 2J feet wide, is fixed so that 
the flame from the grate (G) passes across it into the chimney (B), and at 
one end, the nozzle (N) of a blowing apparatus directs a blast of air over 
the surface of the contents of the cupel. The latter is carefully dried 
by a gradually increasing heat, and is then heated to redness ; the alloy 
of lead and silver, having been previously melted in an iron pot (P) 
fixed by the side of the furnace, is ladled in through a gutter until 
the cupel is nearly filled with it ; a film of oxide soon makes its appear- 
ance upon the surface of the lead, and is fused by the high temperature. 
When the blast is directed upon the surface, it blows off this film of 




Fig. 263. — Cupellation furnace. 



352 EXTRACTION OF LEAD IN THE LABORATORY. 

oxide, and supplies the oxygen for the formation of another film upon 
the clean metallic surface thus exposed. A part of the oxide of lead 
or litharge thus formed is at first absorbed by the porous material of 
the cupel, but the chief part of it is forced by the blast through a 
channel cut for the purpose in the opposite end to that at which the 
blast enters, and is received, as it issues from A, in an iron vessel placed 
beneath the furnace. 

In proportion as the lead is in this manner removed from the 
cupel, fresh portions are supplied from the adjoining melting-pot, and 
the process is continued until about 5 tons of the alloy have been 
added. 

The cupellation is not continued until the whole of the lead has been 
removed, but until only 2 or 3 cwts. of that metal are left in combina- 
tion with the whole of the silver (say 1000 ounces) contained in the 
5 tons of alloy. The metal is run through a hole made in the bottom 
of the cupel, which is then again stopped up so that a fresh charge may 
be introduced. 

The fumes of oxide of lead which are freely evolved during this pro- 
cess are carried off by a hood and chimney (H) situated opposite to the 
blast of air. 

When three or four charges have been cupelled, so as to yield from 
3000 to 5000 ounces of silver, alloyed with 6 or 8 cwts. of lead, the removal 
of the latter metal is completed in another cupel, since some of the silver 
is carried off with the last portions of litharge. 

The appearances indicating the removal of the last portion of lead are 
very striking ; the surface of the molten metal, which has been hitherto 
tarnished, becomes iridescent as the film of oxide of lead thins off, and 
afterwards resplendently bright, and when the cake of refined silver is 
allowed to cool, it throws up from its surface a variety of fantastic 
arborescent excrescences, caused by the escape of oxygen which has been 
mechanically absorbed by the fused silver, and is given off during solidi- 
fication. 

The litharge obtained from the cupelling furnaces is reduced to the 
metallic state by mixing it with small coal, and heating it in a furnace 
similar to that employed in smelting galena. 

251. On the small scale, lead may easily be extracted from galena by mixing 300 
grains with 450 grains of dried carbonate of soda and 20 grains of charcoal, intro- 
ducing the mixture into a crucible, and placing in it two tenpenny nails, heads down- 
wards. The crucible is covered and heated in a moderate fire for about half an hour. 
(A charcoal fire in the small furnace, fig. 132, p. 114, will suffice.) The remainder 
of the nails is carefully removed from the liquid mass, which is then allowed to cool, 
the crucible broken, and the lead extracted and weighed. In this process the 
sulphur of the galena is removed, partly by the sodium of the carbonate, and partly 
by the iron of the nails, the excess of carbonate of soda serving to flux any silica 
with which the galena may be mixed. 

To ascertain if it contains silver, the button is placed in a small bone-ash cupel 
(fig. 264), heated in a muffle (fig. 265) until the whole of the lead is oxidised, 
and absorbed into the bone-ash of the cupel, leaving the minute globule of silver. 

Small globules of lead may be conveniently cupelled on charcoal before the blow- 
pipe, by pressing some bone-ash into a cavity scooped in the charcoal, placing the 
lead upon its surface, and exposing it to a good oxidising flame (p. 105) as long as it 
decreases in size. If any copper be present, the bone-ash will show a green stain 
after cooling. Pure lead gives a yellow stain. 

252. Uses of lead. — The employment of this metal for roofing, &c, 
lias been already noticed. Its fusibility adapts it for casting type for- 



USES OF LEAD. 



353 




printing, but it would be far too soft for this purpose ; accordingly, type- 

metal consists of an alloy of 4 parts of lead 

with 1 of antimony. A similar alloy is used 

for the bullets contained in shrapnel shells, 

since bullets of soft lead would be liable to 

be jammed together, and would not scatter so 

well on the explosion of the shell. On the 

other hand, rifle bullets are made of very pure soft lead, in order that 

they may more easily take the grooves of the rifle. 

Small shot are made of lead to which about 
40 lbs. of arsenic per ton has been added. 
The arsenic dissolves in the lead, hardening 
it and causing it to form spherical drops 
when chilled. The fluid metal is poured 
through a sort of colander fixed at the top of 
a lofty tower (or at the mouth of a deserted 
coal-shaft), and the minute drops into which 
it is thus divided are allowed to fall into a 
vessel of water, after having been chilled by 
the air in their descent. They are afterwards 
sorted, and polished in revolving barrels con- 
taining plumbago. If too little arsenic is 
employed, the shot are elongated or pyri- 
form ; and if the due proportion has been 
exceeded, their form is flattened or lenti- 
cular. 

Common solder is an alloy of equal weights 
of lead and tin, which is more fusible than 
either metal separately. Other alloys con- 
taining lead will be noticed in their proper 
places. 

Leaden vessels are much used in manufac- Fig. 265. 

turing chemistry, on account of the resistance 

of this metal to the action of acids. Neither concentrated sulphuric, hydro- 
chloric, nitric, or hydrofluoric acid, will act upon lead at the ordinary tem- 
perature. The best solvent for the metal is nitric acid of sp. gr. 1 *2, since 
the nitrate of lead, being insoluble in an acid of greater strength, would 
be deposited upon the metal, which it would protect from further 
action. 

Lead is easily corroded in situations where it is brought in contact with 
air highly charged with carbonic acid, when it absorbs oxygen, forming- 
oxide of lead, which combines with carbonic acid and water to produce the 
basic carbonate of lead (PbO.CO,,PbO.H 2 0). The lead of old coffins is 
often found converted into a white earthy-looking brittle mass of basic 
carbonate, with a very thin film of metallic lead inside it. 

When lead is exposed to the joint action of air and the acetic acid con- 
tained in beer, wine, cider, &c, it becomes converted into acetate of lead 
or sugar of lead, which is very poisonous. Hence the accidents arising 
from the reprehensible practice of sweetening cider by keeping it in con- 
tact with lead, and from the accidental presence, in beer and wine bottles, 
of shot which have been employed in cleaning them. The action of water 
upon leaden cisterns has been already noticed. Contact with air and sea- 
water soon converts lead into oxide and chloride. 




354 OXIDES OF LEAD — LITHARGE. 

253. Oxides of lead. — Pour compounds of lead with oxygen are 
known — 

Suboxide of lead, Pb„0 
Oxide „ PbO 

Red oxide ,, Pb 3 4 



Peroxide ,, PbO 




The bright surface of lead soon tarnishes when exposed to the air, 
becoming coated with a dark film, which is believed to consist of suboxide 
of lead. In a very finely divided state, lead takes fire when thrown into 
the air, and is converted into oxide of lead. 

The lead py?wphorus, for exhibiting the spontaneous combustion of lead, is prepared 
by placing some tartrate of lead in a glass tube closed at one end (fig. 266), drawing 
the tube out to a narrow neck near the open end, and 
holding it nearly horizontally, whilst the tartrate of lead 
is heated with a gas or spirit flame as long as any fumes 
are evolved ; the neck is then fused with a blowpipe flame 
and drawn off. The tartrate of lead (PbO.C 4 H 4 5 ), when 
heated, leaves a mixture of metallic lead with charcoal, 
which prevents it from fusing into a compact mass. 
This mixture may be preserved unchanged in the tube 
for any length of time ; but when the neck is broken off 
and the contents scattered into the air, they inflame at 
once, producing thick fumes of oxide of lead. Tartrate 
of lead is prepared by adding ammonia to solution of 
IV. 266. tartaric acid constantly stirred, until the precipitate of 

bitartrate of ammonia at first formed is just redissolved, 
and precipitating the liquid with solution of acetate of lead. The precipitated tar- 
trate of lead is collected upon a filter, washed several times, and dried at a gentle 
heat. 

Oxide or protoxide of lead is prepared on a large scale by heating lead 
in air. When the metal is only moderately heated, the oxide forms a 
yellow powder, which is known in commerce as massicot, but at a higher 
temperature the oxide melts, and on cooling forms a brownish scaly mass 
which is called litharge (XtOog, stone ; apyvpos, silver), probably because 
that obtained by the alchemists would always furnish a considerable pro- 
portion of silver, which was .present in most samples of lead before the 
introduction of Pattinson's process. The litharge of commerce often has 
a red colour, caused by the presence of some red oxide of lead ; from 1 to 
3 per cent, of finely divided metallic lead may also sometimes be found 
in it. When heated to dull redness, litharge assumes a dark brown 
colour, and becomes yellow on cooling. At a bright red heat it fuses, 
and readily attacks clay crucibles, forming a fusible silicate of lead, and 
soon perforating the sides. When boiled with distilled water, litharge is 
dissolved in small quantity, yielding a solution which is decidedly alka- 
line, and becomes turbid when exposed to the air, absorbing carbonic 
acid, and depositing carbonate of lead. The presence of a small quan- 
tity of saline matter in the water hinders the solution of the oxide, but 
organic matter, and especially sugar, favours it. Two definite white 
hydrates of oxide of lead, H 2 0.2PbO and H 2 0.3PbO, maybe obtained by 
precipitating solutions of lead with the alkalies. Oxide of lead is a 
powerful base, and has a strong tendency to form basic salts. Hot solu- 
tions of potash and soda dissolve it readily, and deposit it in pink crystals 
on cooling. 

Litharge, from its easy combination with silicic acid at a high tempera- 



RED LEAD — WHITE LEAD. 355 

ture, is much used in the manufacture of glass, and in glazing earthenware. 
The assayer also employs it as a flux. A mixture of litharge with lime 
is sometimes applied to the hair, which it dyes of a purplish-black colour, 
due to the formation of sulphide of lead from the sulphur existing in hair. 
Dh.il mastic, used by builders in repairing stone, is a mixture of 1 part of 
massicot with 10 parts of brickdust, and enough linseed oil to form a 
paste ; it sets into a very hard mass, which is probably due partly to the 
formation of silicate of lead, and partly to the drying of the linseed oil by 
oxidation favoured by the oxide of lead. 

Red lead or minium is prepared by heating massicot in air to about 
600° F., when it absorbs oxygen, and becomes converted into red lead. 
The massicot for this purpose is prepared by heating lead in a reverberatory 
furnace to a temperature insufficient to fuse the oxide which is formed, 
and rejecting the first portions, which contain-iron and other metals more 
easily oxidisable than lead (as cobalt), as well as the last, which contain 
copper and silver, less easily oxidised than lead. The intermediate pro- 
duct is ground to a fine powder and suspended in water; the coarser 
particles are thus separated from the finer, which are dried, and heated 
on iron trays placed in a reverberatory furnace, till the requisite colour 
has been obtained. Minium is largely used in the manufacture of glass, 
whence it is necessary that it should be free from the oxides of iron, 
copper, cobalt, &c, which would colour the glass. It is also employed as 
a common red mineral colour, and in the manufacture of lucifer-matches. 

When minium is treated with dilute nitric acid, nitrate of lead 
(PbO.N 2 5 ), or Pb(N0 3 ) 2 , is obtained in solution, and peroxide of lead 
(Pb0 2 ) is left as a brown powder, showing that minium is probably a 
compound of the oxide and peroxide of lead. The minium obtained by 
heating massicot in air till no further increase of weight is observed, has 
the composition 2PbO.Pb0 2 , or Pb a 4 , which would appear to represent 
pure minium ; commercial minium, however, has more frequently a com- 
position corresponding to 3PbO.Pb0 2 , but when this is treated with 
potash, PbO is dissolved out, and 2PbO.Pb0 2 remains. Minium evolves 
oxygen at a red heat, becoming PbO, hence the necessity for keeping the 
temperature below 600° P. during its preparation. 

Peroxide, or binoxide, or puce oxide of lead, is found in the mineral 
kingdom as heavy lead ore, forming black, lustrous, six-sided prisms. It 
may be prepared from red lead by boiling it, in fine powder, with nitric 
acid, diluted with five measures of water, washing and drying. The bin- 
oxide of lead easily imparts oxygen to other substances ; sulphur, mixed 
with it, may be ignited by friction, hence this oxide is a common ingre- 
dient in lucifer-match compositions. Its oxidising property is frequently 
turned to account in the laboratory, for example, in absorbing sulphurous 
acid from gaseous mixtures by converting it into sulphate of lead; 
Pb0 2 + S0 2 = PbO.S0 3 . Binoxide of lead is not dissolved by dilute 
acids and has no basic properties ; indeed, it is sometimes called plumbic 
acid, for it combines with potash and soda when fused with their hydrates. 
Plumbate of potash (K 2 O.Pb0 2 .3H 2 0) has been crystallised from an 
alkaline solution, but is decomposed by pure water. 

254. White lead or ceruse is a carbonate of oxide of lead, or, strictly 
speaking, a basic carbonate, a combination of carbonate of oxide of 
lead (PbO.C0. 2 ) with variable proportions of hydrated oxide of lead 
(PbO.H 2 0). This substance is a constant product of the corrosive action 



356 MANUFACTURE OF WHITE LEAD. 

of air and water upon the metal. Its formation is, of course, very much 
encouraged by the presence of organic matters in a state of decay, which 
evolve carbonic acid. 

White lead is manufactured on the large scale by two processes, which 
depend, however, upon the same principle; this may be stated as follows : — 
When oxide of lead is brought in contact with acetic acid (H.C 2 H 3 2 ), 
it forms the acetate of lead (sugar of lead, Pb(C 2 H 3 2 ) 2 ). This salt is 
capable of combining with two molecules of oxide of lead, forming the 
tribasic acetate of lead, Pb(C 2 H 3 2 ) 2 .2PbO, and if this be acted upon 
by carbonic acid, the oxide of lead is converted into carbonate, whilst 
the neutral acetate of lead, Pb(C 2 H 3 2 ) 2 , is left. 

In the older of the two processes, commonly known as the Dutch pro- 
cess, metallic lead, in the form of square gratings cast from the purest 
lead, is placed over earthen pots containing a small quantity of common 
vinegar ; a number of these pots being built up into heaps, together with 
alternate layers of dung or spent tan, the heaps are entirely covered up 
with the same material. The metal is thus exposed to conditions most 
favourable to its oxidation, viz., a very warm and moist atmosphere pro- 
duced by the fermentation of the organic matters composing the heap, 
and the presence of a large quantity of acid vapour generated from the 
acetic acid of the vinegar. The lead is therefore soon converted into 
oxide, a portion of which unites with the acetic acid to form the tribasic 
acetate of lead, which is then decomposed by the carbonic acid devolved 
from the fermenting dung or tan, yielding carbonate of lead, which com- 
bines with another portion of the oxide of lead and of water to form the 
white lead. The neutral acetate of lead left after the removal of the oxide 
of lead from the tribasic acetate, is now ready to take up an additional 
quantity of the oxide, and the process is thus continued until, in the 
course of a few weeks, the lead has become coated with a very thick crust 
of white lead; the heaps are then destroyed, the crust detached, washed, 
to remove adhering acetate of lead, ground to a paste with water, and 
dried. Polled lead is not so easily converted as cast lead. 

The newer process is a more direct application of the same principle, 
for it consists in boiling acetic acid with an excess of litharge in order 
to produce the tribasic acetate of lead, which is afterwards decomposed 
by passing through it a current of carbonic acid obtained by combustion 
or fermentation, or even by exhalation from the earth. The solution of 
neutral acetate of lead is then again boiled with litharge, when tribasic 
acetate is produced, and is again precipitated by the carbonic acid. The 
precipitated carbonate of lead always carries down with it a variable pro- 
portion of the hydrated oxide of lead. This process is, of course, much 
more rapid than the old one, and dispenses with the grinding, which is so 
injurious to the workmen; but the white lead so produced, being crystal- 
line, has less opacity or covering-power (body) than that obtained by the 
Dutch method. 

The usual composition of white lead is expressed by the formula 
PbO.H 2 0, 2(PbO.C0 2 ), though other basic carbonates of lead are often 
mixed with it. 

White lead being very poisonous, its use by painters and others is gene- 
rally attended with symptoms of lead-poisoning, arising in many cases, 
probably, from neglecting to wash the hands before eating, the effect of 
lead being cumulative, so that minute doses may show their combined 
action after many days. Diluted sulphuric acid and solutions of the sul- 



SULPHIDES OF LEAD. 357 

phates of magnesia and the alkalies are sometimes taken internally to 
counteract its effect, since the sulphate of lead is not poisonous. 

All paints containing lead, and cards glazed with white lead, are 
blackened even by minute quantities of sulphuretted hydrogen, from the 
production of black sulphide of lead. If the blackened surface remain 
exposed to the light and air, it is bleached again, the sulphide of lead 
(PbS) being oxidised and converted into white sulphate of lead 
(PbO.S0 3 ), but this does not take place in the dark. A little sulphide 
of lead or powdered charcoal is sometimes mixed with commercial white 
lead to give it a bluish tint. 

The pure carbonate of lead is found in white crystals associated with 
galena. 

Sulphate of lead is found in nature in prismatic and octahedral crystals 
of anglesite or lead-vitriol. It is nearly insoluble in diluted acids, 
and is one of the chief forms in which lead is precipitated from its 
solutions in analytical operations. The minerals lanarkite and leadhillite 
are compounds of sulphate and carbonate of lead. The chromates of 
lead have been already noticed. 

Phosphate of lead (3PbO.P 2 5 ) is occasionally associated with the car- 
bonate in the ores of lead. 

255. Chloride of lead (PbCl 2 ) forms the mineral termed horn-lead. It 
is one of the few chlorides which are not readily soluble in water, and is 
precipitated when hydrochloric acid or a soluble chloride is added to a 
solution of lead. Boiling water dissolves about -fa of its weight of chloride 
of lead, and deposits it in beautiful shining white needles on cooling. It 
fuses easily, and is converted into vapour at a high temperature. 

The oxy chloride of lead (PbCl 2 .PbO) is formed when chloride of lead 
is heated in air. It is sometimes employed as a substitute for white lead 
in painting, being prepared for this purpose by decomposing finely 
powdered galena with concentrated hydrochloric acid (PbS + 2HC1 = 
PbCl 2 + H 2 S), washing the resulting chloride of lead with cold water, dis- 
solving it in hot water, and adding lime-water, which precipitates the 
oxychloride — 

2PbCl 2 + CaO - PbCl 2 .Pb0 + CaCl 2 . 

Turner's yellow (Paris yellow, patent yellow, mineral yellow) is another 
oxychloride of lead (PbCl 2 .7PbO), prepared by heating a mixture of 
litharge and sal-ammoniac. It has a fine golden yellow colour, is easily 
fused, and crystallises in octahedra on cooling. The mineral mendipite 
is an oxychloride of lead (PbCl 2 .2PbO) which occurs in colourless pris- 
matic crystals. 

Iodide of lead (Pbl 2 ) is obtained as a bright yellow precipitate on mix- 
ing solutions of nitrate or acetate of lead and iodide of potassium. If it 
be allowed to settle, the liquid poured off, and the precipitate dissolved 
in boiling water (with one or two drops of hydrochloric acid), it forms a 
colourless solution, depositing golden scales as it cools. 

256. Sulphides of lead. — The subsulphide (Pb 2 S) has been mentioned 
as produced in smelting galena. Sulphide of lead, or galena, has been 
described among the ores of lead. It is always obtained as a black pre- 
cipitate when hydrosulphuric acid or a soluble sulphide acts upon a solu- 
tion containing lead, even in minute proportion. 

A persulphide of lead, the composition of which has not been ascer- 



358 THALLIUM. 

tained, is formed as a red precipitate when a solution of lead is mixed 
with a solution of an alkaline sulphide saturated with sulphur (or with 
solution of hydrosulphate of ammonia which has been kept till it has 
acquired a red colour). 

Clilorosulphide of lead (3PbS.2PbCl 2 ) is obtained as a bright red pre- 
cipitate when hydrosulphuric acid is added in small quantity to a solution 
of chloride of lead in hydrochloric acid. 

Selenide of lead (PbSe) occurs associated with the sulphide in some 
lead ores; it much resembles galena, and has the same crystalline form. 

257. Thallium (Tl = 204 parts by weight). — The discovery of this metal in 1861 
was one of the first results of the application of the new method of testing by obser- 
vation of coloured lines in the spectrum of a flame, described at p. 272. Crookes was 
examining the spectrum obtained by holding in the flame of a Bunsen burner the 
deposit formed in the flues of a sulphuric acid chamber, in which pyrites was 
employed as the source of sulphur. A green line made its appearance in the spectrum, 
which a less acute and practised observer might have mistaken for one of the lines 
caused by barium (see fig. 238), with which it nearly coincides in position ; but the 
line was much brighter than that produced by barium, and on instituting a searching 
analysis of the deposit, a metal was obtained which did not agree in properties with 
any hitherto described, and was named thallium, from 0«xx«t, a young shoot, in 
allusion to the vernal green colour of its spectrum line. It has since been detected 
in several mineral waters ; but the pyrites obtained from Spain and Belgium appear 
to be its best source. From the flue- dust of the sulphuric acid chambers, the metal 
is extracted by a simple process, but large quantities must be operated on to obtain 
any considerable amount. The deposit is treated with boiling water, and the solution 
mixed with much strong hydrochloric acid, which precipitates the thallium as 
chloride ; this is converted into acid sulphate of thallium by treatment with sulphuric 
acid, and this salt having been purified by recrystallisation, is decomposed by zinc, 
which precipitates metallic thallium in a spongy form, fusible into a compact mass 
in an atmosphere of coal-gas. 

In external characters thallium is very similar to lead; but it tarnishes much 
more rapidly when exposed to air, and the streak which it makes on paper soon 
becomes yellowish, being converted into oxide of thallium. If a tarnished. piece of the 
metal be allowed to touch the tongue, a strongly alkaline taste is perceived, for the 
oxide of thallium or thallous oxide (T1 2 0) is very soluble in water, so that the tarnished 
metal becomes bright when immersed in water. The ready solubility of the oxide 
seemed to require thallium to be classed among the alkali-metals, a view which was 
encouraged by the circumstance that its specific heat proved it to be mon atomic like 
potassium and sodium. But thallium appears to be more nearly related to another 
monatomic metal, silver, by the sparing solubility of its chloride and the insolubility 
of its sulphide. The circumstance that it may be kept unaltered in water, and may 
be precipitated from its salts by zinc, at once removes it from the group of alkali- 
metals. The ready solubility of its oxide in water is only an exaggeration of the 
behaviour of the oxides of lead and silver, both of which dissolve slightly in water, 
yielding alkaline solutions. Diluted sulphuric acid acts upon thallium as upon 
zinc, evolving hydrogen. Thallium burns in oxygen with a beautiful green flame, 
and the chlorate of thallium has been recommended for the manufacture of green 
fires in place of chlorate of baryta (see p. 164). The sulphate of thallium, unlike 
that of lead, is easily soluble in water ; the carbonate is father sparingly soluble, 
but far more soluble than carbonate of lead. 

Tlwllic oxide, T1 2 3 , is obtained by adding hypochlorite of soda to thallous chloride 
mixed with excess of carbonate of soda. It is also a basic oxide, its sulphate having 
the composition Tl a O ? .3S0 3 .H 2 0.6Aq. 

Salts of thallium, like those of leacf, are poisonous. 

The equivalent and atomic weights of thallium appear to be identical, and are 
expressed by the number 204. 



AMALGAMATION OF SILVER ORES. 



359 



SILVER 
Ag' =108 parts by weight. 

258. In silver, we meet with the first metal hitherto considered which 
is not capable of undergoing oxidation in the air, under any circum- 
stances, and this, in conjunction with its beautiful appearance, occasions 
its manifold ornamental uses, which are much favoured also by the great 
malleability and ductility of this metal (in which it ranks only second 
to gold), for the former property enables it to be rolled out into thin plates 
or leaves, so that a small quantity of silver suffices to cover a large sur- 
face, whilst its ductility permits the wire-drawer to produce that extremely 
thin silver wire which is employed in the manufacture of silver lace. 

Silver, although pretty widely diffused, is found in comparatively small 
quantity, and hence it bears a high value, which adapts it for a medium 
of currency. 

As might be expected from its want of direct attraction for oxygen, 
silver is found frequently in the metallic or native state, crystallised in 
cubes or octahedra, which are sometimes aggregated together, as in the 
silver-mines of Potosi, into arborescent or dendritic forms. Silver is 
more frequently met with, however, in combination with sulphur, forming 
the sulphide of silver (Ag 2 S), which is generally associated with large 
quantities of the sulphides of lead, antimony, and iron. The largest sup- 
plies of silver are obtained from the Mexican and Peruvian mines, but the 
quantity furnished by Saxony and Hungary is by no means insignificant., 

The process by which silver is extracted from galena has been already 
described under the history of lead. 

The ores of copper (particularly the grey copper-ore) often contain so 
much silver as to be worth working for that metal, in which case they 
are smelted in the usual way, when the copper obtained is found to con- 
tain the whole of the silver present in the ore. This silver is separated 
from the copper by taking advantage of the facility with which the former 
metal is dissolved by melted lead. The process of liquation, as it is 
termed, consists in fusing the argentiferous copper with about thrice its 
weight of lead, and casting the alloy thus obtained into cakes or discs, 
which are afterwards gradually heated upon a" hearth (fig. 267), so con- 
trived that the lead, which melts much more easily than the copper, may 
flow off in the liquid state, carrying with it, in the form of an alloy, the 
silver which was associated with the copper, leaving this last metal in 
porous masses, having the form of the 
original disks, upon the hearth. The 
lead and silver are separated by the 
process of cupellation (p. 351). 

When the extraction of the silver 
is the main object with which a parti- 
cular ore is treated, the process of 
amalgamation is adopted, in which the 
silver is dissolved out by means of 
mercury. At Freiberg, the silver is 
extracted by this method from an ore 
which contains sulphide of silver 
together with much iron pyrites and 
other metallic sulphides. The ore is 
mixed with a small proportion of common salt, and roasted in a rever- 




Fig 267.— Liquation hearth. 



360 



SILVER-PLATING. 




beratory furnace, when the sulphide of silver is converted into chloride of 
silver. It is then ground to a very fine powder, which is agitated, in 
revolving casks, with water and metallic iron, when the latter appro- 
priates the chlorine and reduces the silver to the metallic state. A quan- 
tity of mercury is then introduced into the casks, and the revolution 
continued for several hours ; the mercury dissolves the silver, copper, 
and lead, and is run out of the barrels into stout linen strainers, which 
allow the excess of fluid mercury to pass through, but retain the soft 
solid amalgam containing the silver. In order to recover the silver, this 
amalgam is placed in iron trays arranged one above the other (fig. 268), 
and covered with an iron bell-shaped receiver 
standing over water. By heaping burning fuel 
round the upper part of this dome, its tempera- 
ture is raised sufficiently to convert the mercury 
into vapour, which condenses again in the 
water, leaving the silver, together with the 
copper and lead, upon the iron trays. Finally, 
the silver is refined by fusing it with an addi- 
tional quantity of lead and subjecting the alloy 
to cupellation (p. 351), when the fused oxide 
of lead which is formed carries with it the cop- 
per, also in the form of oxide, leaving the 
silver in a state of purity. 

Various methods have been devised to super- 
sede the amalgamation process. For example, 
Fig. 268. the ores have been roasted with common salt 

to convert the silver into chloride, which is 
dissolved out of the mass by means of a strong solution of common salt, 
from which the silver is afterwards precipitated in the metallic state by 
copper. Hyposulphite of soda has also been employed to dissolve out 
the chloride of silver, and the solution precipitated by sulphide of 
sodium, the resulting sulphide of silver being roasted to remove the sul- 
phur and leave metallic silver. 

Although silver is capable of resisting the oxidising action of the atmo- 
sphere, it is liable to considerable loss by wear and tear in consequence 
of its softness, and is therefore always hardened, for useful purposes, by 
the addition of a small proportion of copper. The standard silver em- 
ployed for coinage and for most articles of silver plate, in this country, 
contains, in 1000 parts, 925 of silver and 75 of copper, whilst that 
used in France contains 900 of silver and 100 of copper. 

Standard silver, for coining and other purposes, is whitened by being 
heated in air and immersed in diluted sulphuric acid, which dissolves out 
the oxide of copper, leaving a superficial film of nearly pure silver. Dead 
or frosted silver is produced in this manner. Oxidised silver is covered 
with a thin film of sulphide by immersion in a solution obtained by 
boiling sulphur with potash. 

The solder employed in working silver consists of 5 parts of silver, 2 
of zinc, and 6 of brass. 

Plated articles are manufactured from copper or one of its alloys, 
which has been united by rolling with a thin plate of silver, the adhesion 
of the latter being promoted by first washing the surface of the copper 
with a solution of nitrate of silver, when a film of this metal is deposited 
upon its surface, the copper taking the place of the silver in the solution. 



PROPERTIES OF SILVER. 361 

Electro-plating consists in covering the surface of baser metals with a 
coating of silver, by connecting them with the negative (or zinc) pole of 
the galvanic battery, and immersing them in a solution made by dissolv- 
ing cyanide of silver in cyanide of potassium ; * the current gradually 
decomposes the cyanide of silver, and this metal is of course (see p. 6) 
deposited upon the object connected with the negative pole, whilst the 
cyanogen liberated at the positive (copper or platinum) pole is allowed to 
act upon a silver plate with which this pole is connected, so that the 
silvering solution is always maintained at the same strength, the quantity 
of silver dissolved at this pole being precisely equal to that deposited at 
the opposite pole. 

Brass and copper are sometimes silvered by rubbing them with a mix- 
ture of 10 parts of chloride of silver with 1 of corrosive sublimate (chlo- 
ride of mercury) and 100 of bitartrate of potash. The silver and mercury 
are both reduced to the metallic state by the baser metal, and an amalgam 
of silver is formed, which readily coats the surface. The acidity of the 
bitartrate of potash promotes the reduction. The surface to be silvered 
should always be cleansed from oxide by momentary immersion in nitric 
acid, and washed with water. .For dry silvering, an amalgam of silver and 
mercury is applied to the clean surface, and the mercury is afterwards 
expelled by heat. 

Silvering upon glass is effected by means of certain organic substances 
which are capable of precijntating metallic silver from its solutions. Look- 
ing-glasses have been made by pouring upon the surface of plates of glass 
a solution containing tartrate of silver and tartrate of ammonia. On heat- 
ing the glass plates to a certain temperature, the oxide of silver contained 
in the tartrate parts with its oxygen to the tartaric acid, and the metallic 
silver is deposited in a closely adhering film. Glass globes and vases are 
silvered internally by a process which is exactly similar in principle. 

Pure silver is easily obtained from standard silver by dissolving it in 
nitric acid, with the aid of heat, diluting the solution with water, adding 
solution of common salt as long as it produces any fresh precipitate of 
chloride of silver, washing the precipitate by decantation as long as the 
washings give a blue tinge with ammonia, and fusing the dried precipitate 
with half its weight of dried carbonate of sooTa in a brisk fire, when a 
button of silver will be found on breaking the crucible — 

2AgCl + lS T a 2 O.C0 2 = Ag 2 + 2NaCl + + C0 2 . 

259. Properties of silver. — The brilliant whiteness of silver distin- 
guishes it from all other metals. It is lighter than lead, its specific 
gravity being 10*53; harder than gold, but not so hard as copper; more 
malleable and ductile than any other metal except gold, which it sur- 
passes in tenacity. It fuses at a somewhat lower temperature than gold or 
copper (about 1870° F.), and is the best conductor of heat and electricity. 
It is not oxidised by dry or moist air, either at the ordinary or at high 
temperatures, but is oxidised by ozone, and tarnished by air containing 
sulphuretted hydrogen, from the production of sulphide of silver, which is 
easily removed by solution of cyanide of potassium. It is unaffected by 
dilute acids, with the exception of nitric ; but hot concentrated sulphuric 
acid converts it into sulphate of silver, and when boiled with strong 
hydrochloric acid, it dissolves to a slight extent in the form of chloride of 

* A solution of cyanide of potassium in 10 parts of water, with 50 grains of chloride of 
silver dissolved in each pint of the liquid, will answer the purpose. 



362 NITRATE OF SILVER. 

silver, which is precipitated on adding water. The hydrates of potash 
and soda do not act on silver to the same extent as on platinum when 
fused with it ; hence silver basins and crucibles are much used in the 
laboratory. 

260. Oxides of silver. — There are three compounds of silver with 
oxygen : the suboxide, Ag 4 ; the oxide, Ag 2 ; and the peroxide, pro- 
bably Ag 2 0. 2 , which is not known in the pure state. The oxide alone has 
any practical interest, as being the base contained in the salts of silver 
with oxygen-acids. 

Oxide of silver (Ag 2 0) is obtained as a brown precipitate when solution 
of nitrate of silver is decomposed by potash. It is a powerful base, 
slightly soluble in water, to which it imparts a weak alkaline reaction. 
A moderate heat decomposes it into its elements. When moist, freshly 
precipitated oxide of silver is covered with a strong solution of ammonia, 
and allowed to stand for some hours, it becomes black, and acquires 
dangerously explosive properties. The composition of this fulminating 
silver is not accurately known, but it is supposed to be a nitride of silver, 
NAg. $ , corresponding in composition to ammonia. 

Nitrate of silver (Ag 2 O.N 2 5 , or AgN0 3 ), or lunar caustic (silver being 
distinguished as luna by the alchemists), is procured by dissolving silver 
in nitric acid, with the aid of a gentle heat, evaporating the solution to 
dryness, and heating the residue till it fuses, in order to expel the excess 
of acid. Tor use in surgery, the fused nitrate is poured into cylindrical 
moulds, so as to cast it into thin sticks • but for chemical purposes it is 
dissolved in water and crystallised, when it forms colourless square tables. 
The action of nitrate of silver as a caustic depends upon the facility with 
which it parts with oxygen, the silver being reduced to the metallic state, 
and the oxygen combining with the elements of the organic matter. This 
effect is very much promoted by exposure to sunlight or diffused daylight. 
Pure nitrate of silver is not changed by exposure to light, but if organic 
matter be present, a black deposit, containing finely divided silver, is pro- 
duced. Thus, the solution of nitrate of silver stains the ringers black 
when exposed to light, but the stain may be removed by cyanide of 
potassium. If solution of nitrate of silver be dropped upon paper, and 
exposed to light, black stains will be produced, and the paper corroded. 
Nitrate of silver is a frequent constituent of marking inks, since the 
deposit of metallic silver formed on exposure to light is not removable by 
washing. The linen is sometimes mordanted by applying a solution of 
carbonate of soda before the marking ink, when the insoluble carbonate 
of silver is precipitated in the fibre, and is more easily blackened than 
the nitrate, especially if a hot iron is applied. Marking inks without pre- 
paration are made with nitrate of silver containing an excess of ammonia, 
which appropriates the nitric acid, and hastens the blackening on 
exposure to light or heat. Hair dyes often contain nitrate of silver. 
The important use of this salt in photography has been noticed already 
(p. 214). 

In order to prepare nitrate of silver from standard silver (containing copper), the 
metal is dissolved in moderately strong nitric acid, and the solution evaporated to 
dryness in a porcelain dish, when a blue residue containing the nitrates of silver and 
copper is obtained. The disli is now moderately heated until the residue has fused, 
and become uniformly black, the blue nitrate of copper being decomposed, and 
leavino- black oxide of copper, at a temperature which is insufficient to decompose the 
nitrate of silver. To ascertain when all the nitrate of copper is decomposed, a small 



IODIDE OF SILVER. 363 

sample is removed on the end of a glass rod, dissolved in water, filtered, and tested 
with ammonia, which will produce a blue colour if any nitrate of copper is left. The 
residue is treated with hot water, the solution filtered from the oxide of copper, and 
evaporated to crystallisation. 

261. Chloride of silver (AgCl) is an important compound, as being 
the form into which, silver is commonly converted in extracting it from 
its ores, and in separating it from other metals. It separates as a white 
curdy precipitate, when solution of hydrochloric acid or a chloride is 
mixed with a solution containing silver. The precipitate is brilliantly 
white at first, but soon becomes violet, and eventually black, if exposed 
to daylight, or more rapidly in sunlight, the chloride of silver being re- 
duced to subchloride (Ag 2 Cl), with separation of chlorine (see p. 214). 
The blackening takes place more rapidly in the presence of an excess of 
nitrate of silver or of organic matter, upon which the liberated chlorine is 
capable of acting. The chloride of silver, formed by suspending silver 
leaf in a bottle of chlorine gas, is not blackened by light. If the white 
chloride of silver be dried in the dark, and heated in a crucible, it fuses 
at about 500° F. to a brownish liquid, which solidifies, on cooling, to a 
transparent, nearly colourless mass, much resembling horn in external 
characters (J torn silver) ; a strong heat converts it into vapour, but does 
not decompose it. If fused chloride of silver be covered with hydro- 
chloric acid, and a piece of zinc placed upon it, it will be found entirely 
reduced, after a few hours, to a cake of metallic silver ; the first portion of 
silver having been reduced in contact with the zinc, and the remainder by 
the galvanic action set up by the contact of the two metals beneath the 
acid. Ammonia readily dissolves chloride of silver, and the solution 
deposits colourless crystals of the chloride when evaporated. If the 
ammonia be very strong, the solution deposits a crystalline compound of 
chloride of silver with ammonia. The absorption of ammoniacal gas by 
chloride of silver has been noticed at p. 123, and the photographic appli- 
cation of the chloride at p. 214. 

Recovery of silver from old jihotographic baths. — One of the simplest methods of 
effecting this consists in mixing the liquid with solution of common salt as long as 
it causes a fresh precipitate of chloride of silver, which is allowed to subside, washed 
once or twice by decantation, mixed with a little sulphuric acid, a lump of zinc 
(spelter) placed in it, and left for a day or two to reduce the silver to the metallic 
state. The zinc is then taken out, and the metallic silver well washed by decanta- 
tion, first, with dilute sulphuric acid, to remove zinc, and afterwards with water, till 
the washings are quite tasteless. It may either be reconverted into nitrate by dissolv- 
ing in nitric acid (p. 362), or fused in an earthen crucible with a little borax. 

From the fixing solutions containing hyposulphite of soda, the silver cannot be 
precipitated by salt, because the chloride of silver is soluble in the hyposulphite. A 
piece of sheet copper left in this for a day or two will precipitate the silver at once 
in the metallic state. 

Subchloride of silver (Ag 2 Cl) has been obtained by the action of per- 
chloride of iron upon metallic silver (Ag 4 + Fe 2 Cl 6 = 2Ag 2 Cl + 2FeCl 2 ). It 
is black and insoluble in nitric acid. Ammonia decomposes it, dissolving 
out chloride of silver, and leaving metallic silver. 

Bromide of silver (AgBr) is a rare Chilian mineral. Associated with 
chloride of silver, it forms the mineral embolite. It much resembles the 
chloride, but is somewhat less easily dissolved by ammonia. 

Iodide of silver (Agl) is also found in the mineral kingdom. It is 
worthy of remark that silver decomposes hydriodic acid much more easily 
than hydrochloric acid, forming iodide of silver, and evolving hydrogen. 



364 EXTRACTION OF MERCURY. 

The iodide of silver dissolves in hot hydriodic acid, and is deposited in 
crystals on cooling. By adding nitrate of silver to iodide of potassium, 
the iodide of silver is obtained as a yellow precipitate which, unlike the 
chloride, does not dissolve in ammonia. Iodide of silver dissolves in a 
boiling saturated solution of nitrate of silver, and the solution, on cooling, 
deposits crystals having the composition AgI.AgN0 3 , which are far more 
sensitive to the action of light than iodide of silver itself, a circumstance 
which is taken advantage of by photographers. The crystals are decom- 
posed by water, with separation of iodide of silver. 

Sulphide of silver (Ag. 2 S) is found as silver glance, which may be 
regarded as the chief ore of silver ; it has a metallic lustre, and is some- 
times found in cubical or octahedral crystals. The minerals known as 
rosielers or red silver ores contain sulphide of silver combined with the 
sulphides of arsenic and antimony. The black precipitate obtained by 
the action of hydrosulphuric acid upon a solution of silver is the sulphide 
of silver. It may also be formed by heating silver with sulphur in a 
covered crucible. Sulphide of silver is remarkable for being soft and 
malleable, so that medals may even be struck from it. It is not dis- 
solved by diluted sulphuric or hydrochloric acid, but nitric acid readily 
dissolves it. Metallic silver dissolves sulphide of silver when fused with 
it, and becomes brittle even when containing only 1 per cent, of the 
sulphide. 



MEECUEY. 

Hg" = 200 parts by weight.* 

262. Mercury (quicksilver) is the only metal which is liquid at the 
ordinary temperature, and since it requires a temperature of 39° below 
zero F. to solidify it, this metal is particularly adapted for the con- 
struction of thermometers and barometers. Its high boiling point 
(662° F.) also recommends it for the former purpose, as does its high 
specific gravity (13*54) for the latter, a column of about 30 inches in 
height being able to counterpoise a column of atmospheric air having 
the same sectional area, and a height equal to that of the atmosphere 
above the level of the sea. The symbol for mercury (Hg) is derived from 
the Latin name for this element, hydrargyrum (vSup, water, referring to 
its fluidity, apyvpov, silver). 

Mercury is not met with in this country, but is obtained from Idria 
(Austria), Almaden (Spain), China, and New Almaden (California). It 
occurs in these mines partly in the metallic state, diffused in minute 
globules or collected in cavities, but chiefly in the state of cinnabar, which 
is a sulphide of mercury (HgS). 

The metal is extracted from the sulphide at Idria by roasting the ore 
in a kiln (fig. 269), which is connected with an extensive series of con- 
densing chambers built of brick-work. The sulphur is converted, by the 
air in the kiln, into sulphurous acid gas, whilst the mercury passes off in 
vapour and condenses in the chambers. 

At Almaden the extraction is conducted upon the same principle, but 
the condensation of the mercury is effected in earthen receivers (called 

* The vapour of mercury is only 100 times as heavy as hydrogen, which would indicate 
100 as the atomic weight of mercury, but the specific heat of mercury when multiplied by 
100 would give an atomic heat only half that of most other metals. 



OXIDATION OF MERCURY. 



365 



aludels) opening into each other, and delivering the mercury into a gutter 
which conveys it to the receptacles. 




Fig. 269.— Extraction of mercury at Idria. 

The cinnabar is placed upon the arch (A, fig. 270) of brick-work, in 
which there are several openings for the passage of the flame of the wood 
fire kindled at B ; this flame 
ignites the sulphide of mercury, 
which burns in the air passing 
up from below, forming sul- 
phurous acid gas and vapour of 
mercury (HgS + 2 = Hg + S0 2 ), 
which escape through the flue 
(F) into the aludels (C), where 
the chief part of the mercury 
condenses, and runs down into 
the gutter (G). The sulphurous 
acid gas escapes through the flue 

(H), and any mercury which may have escaped condensation is collected 
in the trough (D), the gas finally passing out through the chimney (E), 
which provides for the requisite draught. 

In the Palatinate, the cinnabar is distilled in cast-iron retorts with 
lime, when the sulphur is left in the residue as sulphide of calcium, and 
sulphate of lime, whilst the mercury distils over — 




Fig. 270. 



4HgS + 4CaO 



3CaS + CaO.S0 3 + Hg 4 . 



The mercury found in commerce is never perfectly pure, as may be shown by 
scattering a little upon a clean glass plate, when it tails or leaves a track upon the 
glass, which is not the case with pure mercury. Its chief impurity is lead, which 
may be removed by exposing it in a thin layer to the action of nitric acid diluted 
with two measures of water, which should cover its surface, and be allowed to remain 
in contact with it for a day or two, with occasional stirring. The lead is far more 
easily oxidised and dissolved than the mercury, though a little of this also passes 
into solution. The mercury is afterwards well washed with water and dried, first with 
blotting-paper, and then by a gentle heat. Mercury is easily freed from mechanical 
impurities by filtering it through a cone of paper, round the apex of which a few pin- 
holes have been made. 

203. Although mercury in its ordinary condition is not oxidised by air 
at the ordinary temperature, it appears to undergo a partial oxidation 
when reduced to a fine state of division, as in those medicinal prepara- 
tions of the metal which are made by triturating it with various sub- 
stances which have no chemical action upon it, until globules of the metal 
are no longer visible. Blue pill and grey powder, or hydrargyrum cum 



366 USES OF MERCURY. 

cretd, afford examples of this, and probably owe much of their medicinal 
activity to the presence of one of the oxides of mercury. 

264. Uses of mercury. — One of the chief uses to which mercury is 
devoted is the silvering of looking-glasses, which is effected by means of 
an amalgam of tin in the following manner : a sheet of tin-foil of the 
same size as the glass to be silvered is laid perfectly level upon a table, 
and rubbed over with metallic mercury, a thin layer of which is after- 
wards poured upon it. The glass is then carefully slid on to the table, 
so that its edge may carry before it part of the superfluous mercury with 
the impurities upon its surface; heavy weights are laid upon the glass so 
as to squeeze out the excess of mercury, and in a few days the combina- 
tion of tin and mercury is found to have adhered firmly to the glass ; this 
coating usually contains about 1 part of mercury and 4 parts of tin. In 
this and all other arts in which mercury is used (such as barometer-mak- 
ing) much suffering is experienced by the operatives, from the poisonous 
action of the mercury. 

The readiness with which mercury unites with most other metals to 
form amalgams is one of its most striking properties, and is turned to 
account for the extraction of silver and gold from their ores. The attrac- 
tion of the latter metal for mercury is seen in the readiness with which it 
becomes coated with a silvery layer of mercury, whenever it is brought in 
contact with that metal, and if a piece of gold leaf be suspended at a 
little distance above the surface of mercury, it will be found, after a time, 
silvered by the vapour of the metal which rises slowly even at the ordinary 
temperature. From the surface of rings which have been accidentally 
whitened by mercury, it may be removed by a moderate heat, or by warm 
dilute nitric acid, but the gold will afterwards require burnishing. 

Zinc plates are amalgamated, as it is termed, for use in the galvanic 
battery, by rubbing the liquid metal over them under the surface of dilute 
sulphuric acid, which removes the coating of oxide from the surface of 
the zinc. The amalgam of zinc is not acted on by the diluted sulphuric 
acid used in the battery (see p. 4) until the circuit is completed, so that 
no zinc is wasted when the battery is not in use. An amalgam of 6 parts 
of mercury with 1 part of zinc and 1 of tin is also used to promote the 
action of electrical machines. 

The addition of a little amalgam of sodium to metallic mercury gives 
it the power of adhering much more readily to other metals, even to iron. 
Such an addition has been recommended in all cases where metallic sur- 
faces have to be amalgamated, and especially in the extraction of silver 
and gold from their ores by means of mercury. 

Iron and platinum are the only metals in ordinary use which can be 
employed in contact with mercury without being corroded by it. Mer- 
cury, however, adheres to platinum. 

The following definite compounds of mercury with other metals have been 
obtained by combining them with excess of mercury, and squeezing out the fluid metal 
by hydraulic pressure, amounting to CO tons upon the inch: — 

Amalgam of lead, Pb 2 Hg Amalgam of zinc, Zn 2 Hg 

,, silver, AgHg „ copper, CuHg 

,, iron, FeHg ,, platinum, PtHg 2 . 

The amalgam of silver (AgHg) has been found in nature, in dodecahedral crystals. 

A very beautiful crystallisation of the amalgam of silver (Arbor Diance) may be 
obtained in long prisms having the composition Ag 2 Hg 3 , by dissolving 400 grains of 
nitrate of silver in 40 measured ounces of water, adding 160 minims of concentrated 
nitric acid, and 1840 grains of mercury; in the course of a day or two crystals of 
2 or 3 inches in length will be deposited. 



MERCUROUS AND MERCURIC OXIDES. 367 

265. Oxides of mercury . — Two oxides of mercury are known, the sub- 
oxide Hg 2 0, and the oxide HgO ; both combine with acids to form salts. 

Suboxide of mercury, black oxide or mer 'cut vus oxide (Hg 2 0), is obtained 
by decomposing calomel with solution of potash, and washing with water 
(2HgCl + K 2 = Hg 2 + 2KC1). It is very easily decomposed by 
exposure to light or to a gentle heat, into oxide of mercury and metallic 
mercury. 

Bed oxide of mercury or mercuric oxide (HgO), is formed upon the 
surface of mercury, when heated for some time to its boiling point in con- 
tact with air. The oxide is black while hot, but becomes red on cooling. 
It is used, under the name of red precipitate, in ointments, and is prepared 
for this purpose by dissolving mercury in nitric acid, evaporating the 
solution to dryness, and gently calcining the nitrate of mercury (HgO.N 2 5 ) 
until the nitric acid is expelled. The name nitric oxide of mercury refers 
to this process. It is thus obtained, after cooling, as a brilliant red crystal- 
line powder, which becomes nearly black when heated, and is resolved 
into its elements at a red heat. It dissolves slightly in water, and the 
solution has a very feeble alkaline reaction. A bright yellow modification 
of the oxide is precipitated when a solution of corrosive sublimate is 
decomposed by potash (HgCl 2 + K 2 = HgO + 2KC1) \ the yellow variety 
is chemically more active than the red. 

"When oxide of mercury is acted on by strong ammonia, it becomes converted into 
a yellowish white powder which possesses the properties of a strong base, absorbing 
carbonic acid eagerly from the air, and combining readily with other acids. It is 
easily decomposed by exposure to light, and, if rubbed in a mortar when dry, is 
decomposed with slight detonations, a property in which it feebly resembles fulmi- 
nating silver (p. 362). The composition of this substance is represented by the 
formula 4Hg0.2N"H 3 .2H 2 0, and it is sometimes called ammoniated oxide of mercury. 
"When exposed in vacuo over oil of vitriol, it loses 2H 2 0, becoming 4Hg0.2NH 3 , but 
if heated to about 260° F., it oecomes brown ;* it now contains Hg 4 3 N 2 H 4 , and 
may be regarded as a compound of oxide of mercury with two molecules of ammonia 
in which two atoms of hydrogen are displaced by mercury (N 2 H 4 Hg", 3HgO), a view 
which would explain, in a simple manner, the evolution of ammonia when the sub- 
stance is fused with hydrate of potash — 

N 2 H 4 Hg,3HgO + K 2 O.H 2 = 2NH 3 + 4HgO + K 2 0. 

This substance is sometimes called mercuramine; it forms salts with the acids ; the 
sulphate of mercuramine has the composition (N" 2 H 4 Hg,3HgO)S0 3 . 

By passing ammonia gas over the yellow oxide of mercury as long as it is absorbed, 
and heating the compound to about 260° F. in a current of ammonia as long as any 
water is evolved, a brown explosive powder is obtained, which is believed to be a 
nitride of mercury, N 2 Hg 3 ", representing a double molecule of ammonia in which the 
hj-drogen has been displaced by mercury. It yields salts of ammonia when decom- 
posed by hydrated acids. 

266. The salts formed by the oxides of mercury with the oxygen-acids are not of 
great practical importance. Protonitrate of mercury or mercurous nitrate is obtained 
when mercury is dissolved in nitric acid diluted with five volumes of water ; it may 
be procured in crystals having the composition Hg 2 O.N 2 5 ,2Aq. The prismatic 
crystals which are sometimes sold as protonitrate of mercury consist of a basic nitrate, 
3(Hg 2 O.N 2 5 ),Hg 2 O.H 2 0, prepared by acting with diluted nitric acid upon mercury 
in excess. "When this salt is powdered in a mortar with a little common salt, it 
becomes black from the separation of suboxide of mercury — 

3(Hg 2 O.N 2 5 ), Hg 2 O.H 2 + 6NaCl = 6HgCl + 3(Na 2 0.^ T 2 5 ) + Hg 2 + IT 2 ; 

* It has been stated that by heating it for some time in a current of dry ammonia, the 
whole of the oxygen may be expelled as water, leaving the oxide of mercurammonium 
(NHg 2 ") 2 0, which is very explosive, and combines with water to form a hydrate which 
produces salts with the acids. 



.368 MEECUEIC CHLORIDE, OR CORROSIVE SUBLIMATE. 

but the neutral nitrate is not blackened (Hg 2 0. N 2 5 + 2NaCl = 2HgCl + Na 2 0. N 2 5 ). 
These nitrates cannot be dissolved in water without partial decomposition and pre- 
cipitation of yellow basic nitrates. 

Nitrate of mercury or mercuric nitrate is formed when mercury is dissolved with an 
excess of strong nitric acid, and the solution boiled. It is better to prepare it by 
saturating strong nitric acid, diluted with an equal measure of water, with oxide of 
mercury. It may be obtained in crystals of the formula 2(HgO.N 2 5 ),Aq. "Water 
decomposes it, precipitating a yellow basic nitrate, which leaves oxide of mercury 
when long washed with water. 

Sulphate of suboxide of mercury ovmercurous sulphate (Hg 2 O.S0 3 ) is precipitated as 
a white crystalline powder when dilute sulphuric acid is added to a solution of proto- 
nitrate of mercury. 

Sulphate of mercury or mercuric sulphate (HgO. S0 3 ) is obtained by heating 2 parts 
by weight of mercury with 3 parts of oil of vitriol, and evaporating to dryness. Mer- 
curous sulphate is first produced, and is oxidised by the excess of sulphuric acid. It 
forms a white crystalline powder, which is decomposed by water into a soluble acid 
sulphate, and an insoluble yellow basic sulphate of mercury, HgO.S0 3 .2HgO, known 
as turbith or turpeth mineral, said to have been so named from its resembling in its 
medicinal effects the root of the Convolvulus turpethum. 

267. Chlorides of mercury. — The chlorides are the most important 
of the compounds of mercury, the chloride being calomel (HgCl) and the 
bichloride, corrosive sublimate (HgCl 2 ). Vapour of mercury burns in 
chlorine gas, corrosive sublimate being produced.* 

Corrosive sublimate, chloride of mercury, bichloride or perchloride of 
mercury, or mercuric chloride, is manufactured by heating 2 parts by 
weight of mercury with 3 parts of strong sulphuric acid, and evaporating 
to dryness, to obtain mercuric sulphate (Hg + 2(H 2 O.S0 3 ) = HgO.S0 3 + 
2H 2 + S0 3 ), which is mixed with 1|- part of common salt and 
heated in glass vessels (HgO.S0 3 + 2NaCl - Na 2 O.S0 3 + HgCl 2 ), 
when sulphate of soda is left, and the corrosive sublimate is converted 
into vapour, condensing on the cooler part of the vessel in lustrous 
colourless masses, which are very heavy (sp. gr. 5*4), and have a crys- 
talline fracture. It fuses very easily (at 509° E.) to a perfectly colour- 
less liquid, which boils at 563° F., emitting an extremely acrid vapour, 
which destroys the sense of smell for some time. This vapour condenses 
in fine needles, or sometimes in octahedra. Corrosive sublimate dis- 
solves in three times its weight of boiling water, but requires 16 parts 
of cold water, so that the hot solution readily deposits long four-sided 
prismatic crystals of the' salt. It is remarkable that alcohol and ether 
dissolve corrosive sublimate much more easily than water, boiling alcohol 
dissolving about an equal weight of the chloride, and cold ether taking 
up one-third of its weight. By shaking the aqueous solution with ether, 
the greater part of the corrosive sublimate will be removed, and will 
remain dissolved in the ether which rises to the surface. Water in which 
sal-ammoniac has been dissolved will take up corrosive sublimate more 
easily than pure water, a soluble double chloride (sal alembroth) being 
formed, which may be obtained in tabular crystals of the composition 
HgCL,. 6JSTH 4 C1, H 2 0. A solution of corrosive sublimate in water con- 
taining sal-ammoniac is a very efficacious bug-poison.. 

The poisonous properties of corrosive sublimate are very marked, so 
little as three grains having been known to cause death in the case of a 
child. The white of egg is commonly administered as an antidote, because 
it is known to form an insoluble compound with corrosive sublimate, so 
as to render the poison inert in the stomach. The compound of albumen 

* 2 vols, of vapour of corrosive sublimate contain 2 vols, of mercury vapour (see note 
to page 364) and 2 vols, of chlorine. 



CALOMEL OR MEECUBOUS CHLORIDE. 309 

with corrosive sublimate is also much less liable to putrefaction than 
albumen itself, and hence corrosive sublimate is sometimes employed for 
preserving anatomical preparations and for preventing the decay of wood 
(by combining with the vegetable albumen .of the sap). 

Chloride of mercury unites with many other chlorides to form soluble 
double salts, and with oxide of mercury, forming several oxy chlorides of 
mercury, which have no useful applications. 

White jwecipitate, employed for destroying vermin, is deposited when 
a solution of corrosive sublimate is poured into an excess of solution of 
ammonia; HgCl 2 + 2NH 3 = NH 3 .HC1 + ETH 2 Hg" CI. 

White precipitate. 

The true constitution of white precipitate has been the subject of much discussion, 
but the changes which it undergoes, under various circumstances, appear to lead to 
the conclusion that it represents hydrochlorate of ammonia, NH 3 .HC1, in which half 
of the hydrogen has been displaced by mercury. When boiled with potash, it yields 
ammonia and oxide of mercury — 

NH 2 Hg"Cl + KHO = NH 3 + HgO + KC1 . 
If it be boiled with water, it is only partly decomposed in a similar manner, leaving 
a yellow powder having the composition (NH 2 HgCl).HgO, produced according to the 
equation — 

2(NH 2 HgCl) + H 2 = NH3.HCI + (NH 2 HgCl).HgO. 

Yellow precipitate. 

A compound corresponding to this yellow precipitate, but containing chloride of 
mercury in place of the oxide, is precipitated when ammonia is gradually added to 
solution of corrosive sublimate in large excess, the result being a compound of white 
precipitate with a molecule of undecomposed chloride of mercury, — 

(NH 2 HgCl).HgCl 2 . 

If white precipitate be heated to about 600° F., it evolves ammonia, and yields a 
sublimate of ammoniated chloride of mercury, HgCl 2 .NH 3 , leaving a red crystalline 
rjowder which is insoluble in water and in diluted acids, and is unchanged by boiling 
with potash ; it may be represented as a compound of bichloride of mercury with 
ammonia, in which the whole of the hydrogen has been displaced by mercury, 
N 2 Hg 3 ".2HgCl 2 . 

"When solution of corrosive sublimate is added to a hot solution of sal-ammoniac, 
mixed with ammonia, a crystalline deposit is obtained on cooling the liquid, which 
is known as fusible white precipitate, and represents two molecules of hydrochlorate of 
ammonia, in which one-fourth of the hydrogen has been displaced by mercury, its 
composition being N 2 H 6 Hg"Cl 2 . The same compound is formed when white precipi- 
tate is boiled with a solution of sal-ammoniac — 

NH 2 Hg"Cl + NH3.HCI = K 2 H 6 Hg"Cl 2 . 

The above compounds possess a special interest for the chemist, as they were 
among the first to attract attention to the mobility of the hydrogen in ammonia, 
which has since been so well exemplified in the artificial production of organic bases 
by the action of ammonia upon the iodides of the alcohol-radicals. The relation of 
these compounds to each other is here exhibited : — 

White precipitate, NH 2 Hg"Cl 

Produced with corrosive sublimate in excess, . (NH 2 HgCl).HgCl 2 
,, by boihng with water, . . . (NH 2 HgCl).HgO 

,, ,, sal-ammoniac, . . lST 2 H 6 Hg' / Cl 2 

by heating to 600° .... (^ 2 Hg 3 ".2HgCl 2 ) 

268. Calomel, sttbchloride or jwotochloride of mercury, or mercurous 
chloride (HgCl),* unlike corrosive sublimate, is insoluble in water, so that 
it is precipitated when hydrochloric acid or a soluble chloride is added to 
mercurous nitrate. The simplest mode of manufacturing it consists in inti- 
mately mixing one molecule of corrosive sublimate with 1 atom of metallic 

* 2 vols, of vapour of calomel contain 2 vols, of mercury vapour and 1 vol. of chlorine. 
v See note on page 368.) 

2 A 



370 VERMILION OR MERCURIC SULPHIDE. 

mercury, a little water being added to prevent dust, drying the mixture 
thoroughly, and subliming it ; HgCl 2 + Hg = 2HgCL But it is more com- 
monly made by adding another atom of mercury to the materials employed 
in the preparation of corrosive sublimate. 2 parts by weight of mercury 
are dissolved, with the aid of heat, in 3 parts of oil of vitriol, and eva- 
porated to dryness ; Hg + 2(H 2 O.S0 3 ) = HgO.S0 3 + SO, + 2H 2 0. The 
residue of mercuric sulphate is intimately mixed with 2 more parts of 
mercury, and the mixture afterwards triturated with 1 J parts of common 
salt, until globules are no longer visible. The mixture is then heated, so 
that the calomel may pass off in vapour, which condenses as a translucent 
fibrous cake on the cool part of the subliming vessel, leaving sulphate of 
soda behind; HgO.S0 3 + Hg + 2NaCl = 2HgCl + . Na 2 O.S0 3 . For 
medicinal purposes the calomel is obtained in a very fine state of division 
by conducting the vapour into a large chamber, so as to precipitate it in 
a fine powder by contact with a large volume of cold air. Steam is some- 
times introduced to promote its fine division. Sublimed calomel always 
contains some corrosive sublimate, so that it must be thoroughly washed 
with water before being employed in medicine. When perfectly pure 
calomel is sublimed, a little is always decomposed during the process into 
metallic mercury and corrosive sublimate. 

Calomel is met with either as a semitransparent fibrous mass, or an 
amorphous powder, with a slightly yellow tinge. It is heavier than cor- 
rosive sublimate (sp. gr. 7*18), and does not fuse before subliming; it 
may be obtained in four-sided prisms by slow sublimation. Diluted acids 
will not dissolve it, but boiling nitric acid gradually converts it into mer- 
curic chloride and nitrate, which pass into solution. Alkaline solutions 
convert it into black suboxide of mercury, as is seen in black-wash, made 
by treating calomel with lime-water (2HgCl + CaO = Hg 2 + CaCl 2 ). 
Solution of ammonia converts it into. a grey compound (NH 2 Hg 2 Cl), 
which is the analogue of white precipitate (NH 2 Hg"Cl), containing Hg 2 ' 
in place of Hg". 

Mercurous iodide (Hgl) is a green unstable substance, formed when iodine is tri- 
turated with an excess of mercury and a little alcohol. The beautiful scarlet 
mercuric iodide (Hgl 2 ) has been noticed at p. 177. Its vapour has the remarkably 
high specific gravity 15*68. 

If mercuric iodide be dissolved in iodide of potassium, the solution mixed with 
potash, and some ammonia added, a brown precipitate is formed, which may be repre- 
sented by the formula NHg" I. H 2 ; its formation can be explained by the equation, 
2HgI 2 + 3KHO + NH 3 = NHg a I.H s O + SKI + 2H 2 . 

A solution of mercuric iodide in iodide of potassium, mixed with potash, is 
employed as one of the most delicate tests (Nessler's test) for ammonia in waters ; 
5^-ij- gr. of ammonia in half a pint of water is distinctly recognised by the brown 
yellow tinge caused by this test. 

269. Sulphides of mercury. — When mercury is triturated with sulphur, 
the black subsulphide of mercury or mercurous sulphide (Hg 2 S) is formed; 
it was termed by old writers Ethiop's mineral, and is an unstable com- 
pound easily resolvable into metallic mercury and mercuric sulphide (HgS). 
The latter has been mentioned as the principal ore of mercury, and is 
important as composing vermilion. The native sulphide of mercury, or 
cinnabar, is found sometimes in amorphous masses, sometimes crystallised 
in six-sided prisms varying in colour from dark brown to bright red. It 
may be distinguished from most other minerals by its great weight (sp. gr. 
8*2), and by its red colour when scraped with a knife. Neither hydrochloric 
nor nitric acid, separately, will dissolve it, but a mixture of the two dis- 



BISMUTH. 371 

solves it as mercuric chloride, with separation of sulphur. Some speci- 
mens of cinnabar have a bright red colour, so that they only require 
grinding and levigating to be used as vermilion ; and if the brown cinna- 
bar in powder be heated for some time to 120° F. with a solution of sul- 
phur in potash, it is converted into vermilion. 

Of the artificial sulphide of mercury there are two varieties, the black, 
which is precipitated when corrosive sublimate is added to hydrosulphuric 
acid or a soluble sulphide, and the red (vermilion), into which the black 
variety is converted by sublimation, or by prolonged contact with solutions 
of alkaline sulphides containing excess of sulphur, though, so far as is 
known, the conversion is effected without chemical change, the red sul- 
phide having the same composition as the black. In Idria and Holland, 
6 parts of mercury and 1 of sulphur are well agitated together in revolving 
casks for several hours, and the black sulphide thus obtained is sublimed 
in tall earthern pots closed with iron plates, when the vermilion is de- 
posited in the upper part of the pots, and is afterwards ground and 
levigated. The sublimed vermilion, however, is generally inferior to that 
obtained by the wet process, of which there are several modifications. 
One of the processes consists in triturating 300 parts of mercury with 
114 parts of sulphur for two or three hours, and digesting the black 
product, at about 120° F., with 75 parts of hydrate of potash and 400 of 
water until it has acquired a fine red colour. The permanence of vermilion 
paint is, of course, attributable to the circumstance that it resists the 
action of light, of oxygen, carbonic acid, aqueous vapour, and even of the 
sulphuretted hydrogen and sulphurous or sulphuric acid which contaminate 
the air of towns, whereas the red paints containing lead are blackened by 
sulphuretted hydrogen, and all vegetable and animal reds are liable to be 
bleached by atmospheric oxygen and by sulphurous acid. 

When the black precipitated mercuric sulphide is boiled with solution 
of corrosive sublimate, it is converted into a white chlorosulphide of 
mercury, HgCl 2 .2HgS, which is also formed when a small quantity of 
hydrosulphuric acid is added to corrosive sublimate. 

It is remarkable that the molecule of vermilion, HgS, occupies 3 vols, 
instead of 2, containing 2 vols, of mercury vapour combined with 1 vol. 
of sulphur vapour. The anomaly might be explained on the supposition 
that the high temperature requisite to convert the vermilion into vapour 
suffices to suspend the attraction between its elements, so that the vapour 
of which the specific gravity is taken is not really that of the compound 
of mercury and sulphur (which should occupy 2 vols.), but a mixture of 
the 2 vols, of mercury vapour and 1 vol. of sulphur vapour, occupying 
3 vols. This view of the temporary decomposition of the vapour receives 
some slight support from the convertibility of the black into the red 
sulphide by sublimation. 

BISMUTH. 

Bi'" = 210 parts by weight. 

270. Bismuth, though useful in various forms of combination, is too 
brittle to be employed in the pure metallic state. It is readily distin- 
guished from other metals by its peculiar reddish lustre and its highly 
crystalline structure, which is very perceptible upon a freshly broken 
surface; large cubical (or, strictly speaking, rhombohedral) crystals of 
bismuth, are easily obtained by melting a few ounces in a crucible, allow- 



372 



OXIDES OF BISMUTH. 




Fig. 271. — Extraction of bismuth. 



ing it to cool till a crust has formed upon the surface, and pouring out 
the portion which has not yet solidified, when the crystals are found lining 
the interior of the crucible. It is somewhat lighter than lead (sp. gr. 9*8), 
and volatilises more readily at high temperatures. 

Unlike most other metals, bismuth is found chiefly in the metallic state, 
disseminated, in veins, through gneiss and clay-slate. The chief supply 
is derived from the mines of Schneeberg, in Saxony, where it is associated 
with the ores of cobalt. 

In order to extract the metal from the masses of earthy matter through 
which it is distributed, advantage is taken of its very low fusing point 

(507° F.) The ore is broken 
into small pieces, and in- 
troduced into iron cylinders 
which are fixed in an in- 
clined position over a fur- 
nace (fig. 271). The upper 
opening of the cylinders, 
through which the ore is in- 
troduced, is provided with 
an iron door, and the lower 
opening is closed with a 
plate of fire-brick perforated 
for the escape of the metal, 
which flows out when the 
cylinders are heated, into iron receiving pots, which are kept hot by a 
charcoal fire. 

Commercial bismuth generally contains considerable quantities of arsenic, 
sulphur, and silver ; it is sometimes cupelled in the same manner as lead, 
in order to extract. the silver, the oxide of bismuth being afterwards again 
reduced to the metallic state by heating it with charcoal. Pure bismuth 
dissolves entirely and easily in diluted nitric acid (sp. gr. 1*2) ; but if it 
contains arsenic, a white deposit of arseniate of bismuth is obtained. 
Hydrochloric and diluted sulphuric acids will not act upon bismuth. 

The chief use of bismuth is in the preparation of certain alloys with 
other metals. Some kinds of type metal and stereotype metal contain 
bismuth, which confers upon them the property of expanding in the 
mould during solidification, so that they are forced into the finest lines 
of the impression. 

This metal is also remarkable for its tendency to lower the fusing point 
of alloys, which cannot be accounted for merely by referring to the low 
fusing point of the metal itself. Thus, an alloy of 2 parts bismuth, 
1 part lead, and 1 part tin, fuses below the temperature of boiling water, 
although the most fusible of the three metals, tin, requires a temperature 
of 442° F. An alloy of this kind is used for soldering pewter. Bismuth 
is also employed, together with antimony, in the construction of thermo- 
electric piles. 

271. Oxides of bismuth. — Three compounds of bismuth with oxygen have been 
prepared ; bismuthous oxide BiO, bismuthic oxide Bi 2 3 , and bismuthic acid Bi 2 5 . 

Bismuthous oxide (BiO) is obtained as a black precipitate by reducing terchloride 
of bismuth with protochloride of tin in the presence of an excess of potash. It is 
easily converted into bismuthic oxide when heated in contact with air. 

Bismuthic oxide (Bi 2 3 ), is the basic and most important oxide of the. metal. It 
is formed when bismuth is heated in air, or when nitrate of bismuth is decomposed 



ANTIMONY. 373 

by heat, and is a yellow powder which becomes brown when heated, and fuses easily. 
Bismuthic oxide forms the rare mineral bismuth-ochre. 

Bismuthic acid (Bi 2 5 ) is formed when bismuthic oxide is suspended in a strong 
solution of potash through which chlorine is passed, when a red solution of bis- 
muthate of potash is obtained, and hydrated bismuthic acid (H 2 O.Bi 2 5 ) is precipi- 
tated as a red powder, which becomes brown and anhydrous at 270° F. It is easily 
decomposed by heat, evolving oxygen and leaving Bi 2 3 .Bi 2 3 . When heated with 
acids it also evolves oxygen, and forms salts of bismuthic oxide. The bismuthates 
of the alkalies are very unstable, being decomposed by water. 

272. The only two salts of bismuth which are known in the arts are 
the basic nitrate (trisnitrate of bismuth or flake-white) and the oxychloride 
of bismuth (pearl-ivhite). The preparation of these compounds illustrates 
one of the characteristic properties of the salts of bismuth, viz., the facility 
with which they are decomposed by water with the production of in- 
soluble basic salts. 

If bismuth be dissolved in nitric acid, it acquires oxygen from the 
latter, and becomes sesquioxide of bismuth, which combines with nitric acid 
to form the nitrate of bismuth (Bi 2 3 .3N 2 5 ), and this may be obtained 
in prismatic crystals of the composition Bi 2 O 3 .3N 2 O~.10Aq. If the solu- 
tion be mixed with a large quantity of water, it deposits a precipitate of 
flake-white (Bi 2 3 .N 2 5 .H 2 0), or basic nitrate of bismuth, the remainder 
of the nitric acid being left in the solution. 

Pearl-ivhite has the composition 2(BiCl 3 .Bi 2 3 ).H 2 0, and is obtained bv 
dissolving bismuth in nitric acid, and pouring the solution into water in 
which common salt has been dissolved. 

To-chloride of bismuth (BiCl 3 ) may be distilled over when bismuth is heated in a 
current of dry chlorine ; it is a deliquescent fusible solid, easily dissolved by hydro- 
chloric acid, but decomposed by water, with formation of the above-mentioned oxy- 
chloride of bismuth ; 3BiCl 3 + 3H 2 = BiCl 3 . Bi 2 3 + 6HC1. This compound is so 
insoluble in water that nearly every trace of bismuth may be precipitated from a 
moderately acid solution of the terchloride by adding much water. 

Bismuthous sulphide- (BiS) is sometimes found in nature, but more frequently 
bismuthic sulphide (Bi 2 S 3 ) or bismuth glance, which occurs in dark- grey lustrous prisms 
isomorphous with native sulphide of antimony. It is also obtained as a black pre- 
cipitate by the action of hydrosulphuric acid upon bismuthic salts. Bismuthic sul- 
phide is not soluble in diluted sulphuric or hydrochloric acid, but dissolves easily in 
nitric acid. 

ANTIMONY. * 

Sb'" = 122 parts by weight. 

273. Antimony is nearly allied to bismuth in both its physical and 
chemical characters. It is even harder and more brittle than that metal, 
being easily reduced to a black powder. Its bighly crystalline structure 
is another very well-marked feature, and is at once perceived upon the 
surface of an ingot of antimony, where it is exhibited in beautiful fern- 
like markings (star antimony). Its crystals belong to the same system 
(the rhombohedral) as those of bismuth and arsenic. It is much lighter 
than bismuth (sp. gr. 6*715), and requires a higher temperature (800° F.) 
to fuse it, though it is more easily converted into vapour, so that, when 
strongly heated in air, it emits a thick white smoke, the vapour being 
oxidised. Like bismuth, it is but little affected by hydrochloric or dilute 
sulphuric acid, but nitric acid oxidises it, though it dissolves very little 
of the metal, the greater part being left in the form of antimonic acid. 
The best mode of dissolving antimony is to boil it with hydrochloric 
acid and to add nitric acid by degrees. 

Antimony is chiefly found in nature as grey antimony ore or sulphide 



374 AMORPHOUS ANTIMONY. 

of antimony (Sb 2 S 3 ), which occurs in Cornwall, but much more abun- 
dantly in Hungary. It is found in veins associated with galena, iron 
pyrites, quartz, and heavy spar. In order to purify it from these, advan- 
tage is taken of its easy fusibility, the ore being heated upon the hearth 
of a reverberatory furnace, with some charcoal to prevent oxidation, when 
the sulphide of antimony melts and collects below the impurities, whence 
it is run off and cast into moulds. The product thus obtained is known 
in commerce as crude antimony, and contains sulphides of arsenic, iron, 
and lead. 

To obtain regulus of antimony or metallic antimony, the sulphide of 
antimony is sometimes fused in contact with refuse metallic iron (such as 
the clippings of tin-plate), when sulphide of iron is formed, and collects 
as a fused slag upon the surface of the melted antimony — 
Sb 2 S 3 + Fe g = 3FeS + Sb 2 . 

The antimony thus obtained always contains a considerable proportion of 
iron. 

A purer product is procured by another process, which consists in 
roasting the sulphide in a reverberatory furnace at a temperature insuffi- 
cient to fuse it, for about twelve hours, when most of the sulphur and 
arsenic are expelled as sulphurous and arsenious acids, carrying with them 
a considerable quantity of oxide of antimony. The roasted ore has a 
brown-red colour, and contains both oxide and sulphide of antimony : 
it is mixed into a paste with -J- its weight of charcoal saturated with a 
strong solution of carbonate of soda. The mixture is strongly heated in 
crucibles, when the oxide of antimony is reduced by the charcoal, and a 
portion of the sulphide, having been converted into oxide by double 
decomposition with the soda (8^83 + 3^20 = 8^03 + 3^28), is also 
reduced, the remainder of the sulphide combining with the sulphide of 
sodium to form a slag which floats above the metallic antimony ; the lat- 
ter is cast into ingots for the market, and the slag, known as crocus of 
antimony (chiefly 3Na 2 S.Sb 2 S 3 ), is employed for the preparation of some 
of the compounds of the metal. 

On the small scale, antimony may be extracted from the sulphide by fusing it in 
an earthen crucible with 4 parts of commercial cyanide of potassium, at a moderate 
heat ; or by mixing 4 parts of the sulphide with 3 of bitartrate of potash and 1| of 
nitre, and throwing the mixture, by small portions, into a red-hot crucible, when 
the sulphur is oxidised, and converted into sulphate of potash, by the nitre, which is 
not present in sufficient quantity to oxidise the antimony, so that the metal collects 
at the bottom of the crucible. 

The brittleness of antimony renders it useless in the metallic state 
except for the construction of thermo-electric piles, where it is employed 
in conjunction with bismuth. Antimony is employed, however, to 
harden several useful alloys, such as type-metal, shrapnel-shell bullets, 
Britannia metal, and pewter. 

Amorphous antimony. — The ordinary crystalline form of antimony may be obtained, 
like copper and other metals, by decomposing solutions containing the metal by 
transmitting the galvanic current ; but in some cases the antimony is deposited from 
very strong solutions in an amorphous condition, having properties very different 
from those of ordinary antimony. The best mode of obtaining it in this form is to 
decompose a solution of 1 part of tartar emetic (tartrate of antimony and potash) in 
4 parts of a strong solution of terchloride of antimony (obtained by heating hydro- 
chloric acid with sulphide of antimony till it refuses to dissolve any more), by the ' 
aid of three cells of Smee's battery, the zinc of which is connected by a copper wire 
with a plate of copper immersed in the antimonial solution, whilst the platinised 
silver of the battery is connected with a plate of antimony in the same solution, at 



OXIDES OF ANTIMONY. 375 

some little distance from the copper plate. The deposit of antimony which forms 
upon the copper has a brilliant metallic appearance, but is amorphous, and not 
crystalline, like the ordinary metal. If it be gently heated or sharply struck, its 
temperature suddenly rises to about 400°, and it becomes converted into a form more 
nearly resembling crystalline antimony. At the same time, however, thick fumes 
of terchloride of antimony are evolved, for this substance is always present in the 
amorphous antimony to the amount of 5 or 6 per cent.,* so that, as yet, there is not 
sufficient evidence to establish beyond a doubt the existence of a pure amorphous 
form of antimony corresponding to amorphous phosphorus, however probable this 
may appear from the chemical resemblance between these elements. 

274. Oxides of antimony. — There are two well-known oxides of anti- 
mony, the sesqnioxide (Sb 2 OJ and antimonic acid (Sb 2 5 ). Teroxide or 
sesquioxide of antimony, or antimonic oxide, is formed when antimony 
burns in air, and is prepared on a large scale by roasting either the metal 
or the sulphide in air, for use in painting as a substitute for white lead. 
It is also found in nature as white antimony ore or valentinite. Antimonic 
oxide forms a crystalline powder usually composed of minute prisms 
having the shape of the rarer form of arsenious acid (p. 250), whilst occa- 
sionally it is obtained in crystals similar to those of the common octahedral 
arsenious acid, with which, therefore, antimonic oxide is isodimorphous.f 
When heated in air it assumes a yellow colour, afterwards takes fire, 
smoulders, and becomes converted into the antimoniate of teroxide of 
antimony (Sb 2 3 .Sb 2 5 — Sb 2 4 ), which was formerly regarded as an inde- 
pendent oxide. The teroxide is insoluble in water, but acids dissolve it, 
forming salts, though its basic properties are weak, and its salts rather ill 
defined. Potash and soda are also capable of dissolving it, whence it is 
sometimes called antimonious acid, % 

Antimonic acid (Sb 2 5 ) is formed when antimony is oxidised with nitric 
acid ; it then forms a white powder, which should be well washed and 
dried. When heated it becomes pale yellow, and is decomposed at a high 
temperature, leaving Sb.,C 3 .Sb 2 5 . It is dissolved by solution of potash 
forming antimoniate of potash. 

A better method of obtaining the antimoniate of potash consists in 
gradually adding 1 part of powdered antimony to 4 parts of nitre fused in 
a clay crucible, when the oxygen of the nitre converts the antimony into 
antimonic acid, which combines with the potash. The mass is powdered 
and washed with warm water to remove the excess of nitre and the nitrate 
of potash, when the insoluble anhydrous antimoniate of potash is left ; 
and on boiling this for an hour or two with water, it becomes hydrated 
and dissolves. The solution, when evaporated, leaves a gummy mass of 
antimoniate of potash, having the composition K 2 O.Sb 2 6 .5Aq. 

When the solution of antimoniate of potash is treated with carbonic 
acid, a crystalline precipitate of biantimoniate of potash (K 2 0.2Sb 2 5 ) is 
obtained. If antimoniate of potash be fused (in a silver crucible) with 
hydrate of potash, it becomes converted into metantimoniate of potash 
(2K 2 O.Sb 2 5 ), which is decomposed by water into potash and bimetan- 
timoniate of potash (K 2 O.H 2 O.Sb 2 5 ), which may be crystallised from the 
solution. This latter salt is valuable as a test for soda, since the bimetan- 

* It has been plausibly suggested that the sudden rise of temperature may be due to 
the presence of an antimony compound analogous to the so-called chloride of nitrogen, the 
latter element being connected with antimony by several chemical analogies. 

f The octahedral form appears to be produced only when the prismatic form is slowly 
sublimed in a non-oxidising atmosphere. The mineral exitele is prismatic oxide of anti- 
mony, and senarmontite is the octahedral form of that oxide. 

X Two crystallised antimonites of soda have been obtained, the neutral antimonite 
Na 2 O.Sb 2 3 .6Aq., and the terantimonite Na 2 0.3Sb 2 3 .2Aq. ; the former is sparingly 
soluble, the latter almost insoluble in water. 



376 



CHLORIDES OF ANTIMONY. 




Fig. 272. 



timoniate of soda, Na 2 O.H 2 O.Sb 2 5 , is one of the very few salts of soda 
which are insoluble in water, and is therefore obtained as a crystalline 
precipitate when the bimetantimoniate of potash is added to a solution 
containing soda. The solution of bimetantimoniate of potash is gradually 
changed by keeping, into an timoniate of potash (K 2 O.Sb 2 5 ), which does 
not so readily precipitate soda. 

It will be remarked that the antimoniates correspond in composition 
with the monobasic (or meta) phosphates, whilst the metantimoniates 
represent the bibasic (or pyro) phosphates. 

Naples yellow is a compound of antimonic acid with oxide of lead. 

275. Antimonietted hydrogen (SbH 3 ?) is obtained, mixed with free 
hydrogen, when an alloy of zinc and antimony is acted on by diluted sul- 
phuric acid, or when a solution of a salt of antimony (tartar emetic, for 
example) is poured into a hydrogen apparatus containing zinc and dilute 
sulphuric acid (fig. 272). If the gas be inflamed as it issues into the air, 
it burns with a livid flame, emitting fumes of anti- 
monic oxide, and when a piece of glass or porcelain is 
depressed in the flame (fig. 273) it becomes coated with 
a black film of metallic antimony. A red heat decom- 
poses the gas into its elements, so that if the tube 
through which it is passing be heated with a spirit 
lamp (fig. 274) a lustrous black deposit of antimony 
will be formed just beyond the heated part. The 
composition of antimonietted hydrogen is not certainly 
established, since it has never been obtained unmixed 
with hydrogen ; but it is believed to contain SbH 3 , 
because, when passed into nitrate of silver, it gives a black precipitate 
containing SbAg 3 . It would then be analogous to ammonia (NH 3 ), 
phosphuretted hydrogen (PH 3 ), and arsenietted hydro- 
gen (AsH 3 ). Very minute quantities of antimony are 
detected in chemical analysis by converting it into this 

form. 
Fig. 273. 

276. Chlorides of antimony. — Chlorine and anti- 
mony combine readily, with evolution of heat and light ; the chlorides 
are among the most important compounds of this metal. 

Terchloride of antimony (SbCl 3 ) may be prepared by distilling 3 parts 
of powdered antimony with 8 parts of corrosive sublimate, when calo- 
mel and an amalgam of antimony are left, 
and the terchloride of antimony (boiling 
at 433° F.) distils over- 
go, + 2HgCl 2 = SbCl 3 + SbHg + HgCl. 

It can also be obtained by boiling pow- 
dered antimony or sulphide of antimony to 
dryness with strong sulphuric acid, and 
distilling the sulphate of teroxide of anti- 
mony thus obtained, with common salt. 
The terchloride is a soft grey crystalline 
fusible solid, whence its old name of butter 
„ v _ of antimony. It may be dissolved in a 

small quantity of water, but a large quantity 
of water decomposes it, forming a bulky white precipitate, which is an 




SULPHIDES OF ANTIMONY. 377 

oxycliloride of antimony (3SbCl 3 + 3H 2 = SbCl 3 .Sb 2 3 + 6HC1). 
When hot water is added to a hot solution of terchloride of antimony in 
hydrochloric acid, minute prismatic needles are deposited, containing 
2SbCLj.5Sb 2 3 , and formerly called powder of Algaroth. The terchloride 
of antimony, in its behaviour with water, much resembles that of bismuth. 
Terchloride of antimony is occasionally used in surgery as a caustic ; it 
also serves as a bronze for gun-barrels, upon which it deposits a film of 
antimony. 

Pentachloride of antimony (SbCL) is prepared by heating coarsely 
powdered antimony in a retort, through which a stream of dry chlorine is 
passed (fig. 216), the neck of the retort being fitted into an adapter, which 
serves to condense the pentachloride. One ounce of antimony will require 
the chlorine from about 6 oz. of common manganese and 18 oz. (measured) 
of hydrochloric acid. The pure pentachloride is a colourless fuming liquid 
of a very suffocating odour; it combines energetically with a small 
quantity of water, forming a crystalline hydrate, but an excess of water 
decomposes it into hydrochloric and hydrated metantimonic acids, the 
latter forming a white precipitate — 

2SbCl 5 + 7H 2 = 10HC1 + 2H 2 O.Sb 2 5 . 

Pentachloride of antimony is employed by the chemist as a chlorinating 
agent ; thus, defiant gas (C 2 H 4 ) when passed through it, is converted into 
Dutch liquid (C 2 H 4 C1 2 ), and carbonic oxide into phosgene gas, the penta- 
chloride of antimony being converted into terchloride. 

The pentachloride of antimony is the analogue of pentachloride of phos- 
phorus, and a clilorosidpliide of antimony (SbCl 3 S), corresponding to 
chlorosulphide of phosphorus, is obtained as a white crystalline solid by 
the action of hydrosulphuric acid upon pentachloride of antimony. 

277. Sulphides of antimony. — The tersulphide or sesauisulphide of 
antimony (Sb 2 S 3 ) has been noticed as the chief ore of antimony. It is a 
heavy mineral (sp. gr. 4 "6 3) of a dark-grey colour and metallic lustre, 
occurring in masses which are made up of long prismatic needles. It fuses 
easily, and may be sublimed unchanged out of contact with air. It is 
easily recognised by heating it, in powder, with hydrochloric acid, when 
it evolves the odour of hydrosulphuric acid, and-if the solution be poured 
into water, it deposits an orange precipitate. This orange sulphide, which 
has the same composition as the grey sulphide, is also obtained by adding 
hydrosulphuric acid to a solution of a salt of antimony (for example, tartar- 
emetic) acidulated with hydrochloric acid. It may be converted into the 
grey sulphide by the action of heat. The orange variety constitutes the 
antimony vermilion, the preparation of which has been described at p. 214. 
Native tersulphide of antimony is employed, in conjunction with chlorate 
of potash, in the friction-tube for firing cannon ; it is also used in percus- 
sion caps, together with chlorate of potash and fulminate of mercury. Its 
property of deflagrating with a bluish-white flame when heated with nitre, 
renders it useful in compositions for coloured fires. 

Glass of antimony is a transparent red mass obtained by roasting the 
tersulphide of antimony in air, and fusing the product ; it contains about 
8 parts of teroxide and 1 part of tersulphide of antimony. 

Red antimony ore is an oxysulphide of antimony, Sb 2 O a .2Sb 2 S 3 . 

Pentasidphide of antimony (Sb 2 S 5 ) is obtained as a bright orange-red 
precipitate by the action of hydrosulphuric acid upon a solution of penta- 
chloride of antimony in hydrochloric acid. 



378 EXTRACTION OF TIN FROM TIN-STONE. 

Both the sulphides of antimony are sulphur-acids, capable of combining 
with the alkaline sulphides to form sidphantimonites and sulphantimoniates 
respectively. Hence they are easily dissolved by alkalies and alkaline 
sulphides. Even metallic antimony, in powder, is dissolved when gently 
heated with solution of sulphide of potassium in which sulphur has been 
dissolved, any lead or iron which may be present being left in the residue, 
so that the antimony may be tested by this process as to its freedom from 
those metals. 

Mineral kermes is a variable mixture of sesquioxide and sesquisulphide 
of antimony, which is deposited as a reddish- brown powder from the solu- 
tion obtained by boiling sesquisulphide of antimony with potash or soda. 
It was formerly much valued for medicinal purposes. 

Schlippe's salt is the sulphantimoniate of sulphide of sodium 
(3ISra 2 S, Sb 2 S 5 , 18H 2 0) and may be obtained in fine transparent tetrahedral 
crystals. 

TIN. 

Sn = 118 parts by weight. 

278. Tin is by no means so widely diffused as most of the other metals 
which are largely used, and is scarcely ever found in the metallic state in 
nature. Its only important ore is that known as tin-stone, which is a 
binoxide of tin (Sn0 2 ), and is generally found in veins traversing quartz, 
granite, or slate. It is generally associated with arsenical iron pyrites, 
and with a mineral called wolfram, which is a compound of tungstic acid 
(W0 3 ) with the oxides of iron and manganese. 

Tin-stone is sometimes found in alluvial soils in the form of detached 
rounded masses ; it is then called stream tin ore, and is much purer than 
that found in veins, for it has undergone a natural process of oxidation 
and levigation exactly similar to the artificial treatment of the impure ore. 
These detached masses of stream tin ore are not unfrequently rectangular 
prisms with pyramidal terminations. 

The Cornish mines furnish the largest supplies of tin, and those of 
Malacca and Banca stand next. Tin-stone is also found in Bohemia, 
Saxony, and California. 4-t the Cornish tin-works the purer portions of 
the ore are picked out by hand, and the residue, which contains quartz 
and other earthy impurities, together with copper pyrites and arsenical 
iron pyrites, is reduced to a coarse powder in the stamping-mills, and 
washed in a stream of water. The tin-stone, being extremely hard, is not. 
reduced to so fine a powder as the pyritous minerals associated with it, 
and these latter are therefore more readily carried away by the stream of 
water than the tin-stone. The removal of the foreign matters from the 
ore is also much favoured by the high specific gravity of the binoxide of 
tin, which is 6'5, whilst that of sand or quartz is only 2*7, so that the 
latter would be carried off by a stream which would not disturb the former. 
So easily and completely can this separation be effected, that a sand con- 
taining less than one per cent, of tin-stone is found capable of being 
economically treated. 

In order to expel any arsenic and sulphur which may still remain in 
the washed ore, it is roasted in quantities of 8 or 1 cwts. in a reverbera- 
tory furnace, when the sulphur is disengaged in the form of sulphurous 
acid, and the arsenic in that of arsenious acid, the iron being left in the 
state of sesquioxide, and the copper partly as sulphate of copper, partly 



PURIFICATION OF TIN. 



379 



as unaltered sulphide, To complete tlie oxidation of the insoluble sulphide 
of copper, and its conversion into the soluble sulphate, the roasted ore is 
moistened with water and exposed to the air for some days, after which 
the whole of the copper may be removed by again washing with water. 

A second washing in a stream of water also removes the sesquioxide of 
iron in a state of suspension, and this is much more easily effected than 
when the iron was in the form of pyrites, since the difference between the 
specific gravity of this mineral (5*0) and that of the tin-stone (6*5) is far 
less than that between sesquioxide of iron and tin-stone. 

The ore thus purified contains between 60 and 70 per cent, of tin ; it 
is mixed very intimately with about -J- of powdered coal, and a little lime 
or fluor spar to form a fusible slag with the earthy impurities ; the mix- 
ture is sprinkled with water to prevent its dispersion by the draught 
of air, and thrown on the hearth (A, fig. 275) of a reverberatory furnace, 
in charges of between 20 and 25 cwts. 

The temperature is not permitted to rise too high at first, lest a portion 
of the oxide of tin should combine 
with the silicic acid to form a sili- 
cate, from which the metal would 
be reduced with difficulty. 

During the first 6 or 8 hours the 
doors of the furnace are kept shut, 
so as to exclude the air and favour 



the reducing action of the carbon 
upon the binoxide of tin, the oxy- 
gen of which it converts into car- 
bonic oxide, leaving the tin in the 
metallic state to accumulate upon 
the hearth beneath the layer of slag. 
When the reduction is deemed com- 
plete, the mass is well stirred with 
an iron paddle to separate the metal 
from the slag; the latter is run out 
first, and the tin is then drawn off 
into an iron pan (B), where it is 
allowed to remain at rest for the 
dross to rise to the surface, and is 
ladled out into ingot-moulds. 

The slags drawn out of the smelting-furnace are carefully sorted, those 
which contain much oxide of tin being worked up with the next charge 
of ore, whilst those in which globules of metallic tin are disseminated are 
crushed, so that the metal may be separated by washing in a stream of water. 

The tin, wheu first extracted from the ore, is far from pure, being con- 
taminated with small quantities of iron, arsenic, copper, and tungsten. 
In order to purify it from these, the ingots are piled into a hollow heap 
near the fire-bridge of a reverberatory furnace, and gradually heated to the 
fusing point, when the greater portion of the tin flows into an outer basin, 
whilst the remainder is converted into the binoxide, which remains as 
dross upon the hearth, together with the oxides of iron, copper, and tung- 
sten, the arsenic having passed off in the form of arsenious acid. Fresh 
ingots of tin are introduced at intervals, until about 5 tons of the metal 
have collected in the basin, which is commonly the case in about an hour 
after the commencement of the operation. 




Fig. 275. 



380 MANUFACTURE OF TIN-PLATE. 

The specific gravity of tin being very low (7*285), any dross which 
may still remain mingled with it does not separate very readily ; to 
obviate this, the molten metal is well agitated by stirring with wet 
wooden poles, or lowering billets of wet wood into it, when the evolved 
bubbles of steam carry the impurities up to the surface in a kind of froth ; 
the stirring is continued for about three hours, and the metal is allowed to 
remain at rest for two hours, when it is skimmed and ladled into ingot- 
moulds. It is found that, in consequence of the lightness of the metal, 
and its tendency to separate from the other metals with which it is con- 
taminated, the ingots which are cast from the metal first ladled out of the 
pot are purer than those from the bottom ; this is shown by striking the 
hot ingots with a hammer, when they break up into the irregular prismatic 
fragments known as dropped or grain-tin, the impure metal not exhibiting 
this extreme brittleness at a high temperature. The tin imported from 
Banca is celebrated for its purity (Straits tin). 

When the tin ore contains wolfram, it is usual to purify it before smelt- 
ing, by fusion with carbonate of soda in a reverberatory furnace, when 
the tungstic acid is converted into tungstate of soda, which is dissolved 
out by water and crystallised. This salt finds an application in calico- 
printing. 

On the small scale, tin may be extracted from tin-stone, by fusing 100 
grains with 20 grains of dried carbonate of soda, and 20 of dried borax, 
in a crucible lined with charcoal, exactly as in the extraction of iron (see 
p. 319). 

279. By its physical characters, tin is very readily distinguished from 
other metals. If a bar of tin be bent, it emits a peculiar crackling sound. 
With the exception of lead and zinc, it is the least tenacious of all the 
metals in common use ; its ductility is therefore very low, and lead is the 
only common metal which is more difficult to draw into wire at the ordi- 
nary temperature. Tin may, however, be drawn at 212° F. 

In fusibility, tin surpasses all the other common metals, becoming 
liquid at 442° F., but it is not easily vaporised. Its malleability is also 
very great, only gold, silver, and copper exhibiting this quality in a higher 
degree. This malleability is shown in the manufacture of tin-foil, where 
plates of the best tin are hammered down to a certain thinness, then cut 
up, laid upon each other, and again beaten till extended to the required 
degree. 

Tin-plate, it must be remembered, is made in a very different way, by 
coating sheets of iron with a layer of tin • the best kind, known as block 
tin, being that which is covered with the thickest layer of tin, and after- 
wards hammered upon a polished anvil in order to consolidate the coating 
and make it adhere more firmly. Tin, being unaltered by exposure to air 
at the ordinary temperature, will effectually protect the iron from rust as 
long as the coating of tin is perfect, but as soon as a portion of the tin is 
removed so as to leave the iron exposed, corrosion will take place very 
rapidly, because the two metals form a galvanic couple, which will decom- 
pose the water (charged with carbonic acid) deposited upon them from 
the air, and the iron, having the greater attraction for oxygen, will be the 
metal attacked. In the case of galvanised iron (coated with zinc), on the 
contrary, the zinc would be the metal attacked, and hence the greater 
durability of this material under certain conditions. 

For the manufacture af tin-plate, the very best iron refined with char- 



GUN-METAL. 381 

coal (see p. 308) is employed, and the most important part of the process 
consists in cleansing the iron plates from every trace of oxide which would 
prevent the adhesion of the tin. To effect this they are made to undergo 
several processes, of which the most important are — (1), immersion in 
dilated sulphuric acid ; (2), heating to redness ; (3), hammering and roll- 
ing to scale off the oxide ; (4), steeping in sour bran ; (5), immersion in 
mixed diluted sulphuric and hydrochloric acids ; (6), scouring with bran ; 
(7), washing with water; they are then dried for an hour in a vessel of 
melted tallow which prevents contact of air, and immersed for an hour 
and a half in melted tin, the surface of which is protected from oxidation 
by tallow ; after draining, they are dipped a second time into the tin to 
thicken the layer ; then transferred to a bath of hot tallow to allow the 
superfluous tin to run down to the lower edge, whence it is afterwards 
removed by liquefying it in a vessel of melted tin, and shaking it off by 
a sharp blow. About 8 lbs. of tin are required to cover 225 plates, 
weighing 112 lbs. 

Terne-plate is iron coated with an alloy of tin and lead. 

In tinning the interior of copper vessels, in order to prevent the con- 
tamination of food with the copper, the surface is first thoroughly cleaned 
from oxide by heating it and rubbing over it a little sal-ammoniac (hydro- 
chlorate of ammonia, ISTHg.HCl), which decomposes any oxide of copper, 
converting it into the volatile chloride of copper (CuO + 2(NH 3 .HC1) = 
CuCl 2 + H 2 + 2NH 3 ). A little resin is then sprinkled upon the 
metallic surface, to protect it from oxidation, and the melted tin is spread 
over it with tow. 

Pins (made of brass wire) are coated with tin by boiling them with 
cream of tartar (bitartrate of potash), common salt, alum, granulated tin, 
and water ; the tin is oxidised at the expense of the water, and is then 
dissolved by the acid liquid, from which solution it is reduced by elec- 
trolytic action, for the tin is more highly electro-positive than the brass, 
and the latter acts as the negative plate. 

280. Alloys of tin. — The solder employed for tin wares is an alloy of 
tin and lead in various proportions, sometimes containing 2 parts of tin 
to 1 of lead (fine solder), sometimes equal weights of the two metals 
(common solder), and sometimes 2 parts of lead to 1 of tin (coarse solder). 
All these alloys melt at a lower temperature than tin, and, therefore, than 
lead. In applying solder, it is essential that the surfaces to be united be 
quite free from oxide, which would prevent the adhesion of the solder ; 
this is insured by the application of sal-ammoniac, or of hydrochloric 
acid,* or sometimes of powdered borax, remarkable for its ready fusibility 
and its solvent power for the metallic oxides. 

Tin forms the chief part of the alloys known as pewter and Britannia 
metal, the former being composed of about 4 parts of tin and 1 of lead, 
whilst the latter contains, in addition to the tin, comparatively small 
quantities of antimony, copper, and lead. Another similar alloy is com- 
posed of 12 parts of tin, 1 of antimony, and a little copper. 

Gun metal is an alloy of 90*5 parts of copper with 9*5 of tin, especially 
valuable for its tenacity, hardness, and fusibility. In preparing this 
alloy, it is usual to melt the tin, in the first place, with twice its weight 
of copper, when a white, hard, and extremely brittle alloy (hard metal) is 

* It is customary to kill the hydrochloric acid by dissolving some zinc in it. The 
chloride of zinc is probably useful in protecting the work from oxidation. 



382 PROPERTIES OF TIN. 

obtained. The remainder of the copper is fused in a deoxidising flame 
on the hearth of a reverberatory furnace, and the hard metal thoroughly 
mixed with it, long wooden stirrers being employed. A quantity of old 
gun metal is usually melted with the copper, and facilitates the mixing of 
the metals. "When the metals are thoroughly mixed, the oxide is re- 
moved from the surface, and the gun metal is run into moulds made of 
loam, the stirring being continued during the running, in order to prevent 
the separation, to which this alloy is very liable, of a white alloy contain- 
ing a larger proportion of tin, which has a lower specific gravity, and 
would chiefly collect in the upper part of the casting. In casting cannon 
(erroneously called brass guns), the mould is placed perpendicularly with 
the muzzle upwards, the upper part of the mould being about 3 feet 
longer than is required for the gun, so that a superfluous cylinder of metal 
or dead-head is formed, in which the separated alloy collects, together 
with any oxide or dross which may have run out with the metal ; pro- 
bably, also, the weight of this column of metal hastens the solidification 
and hinders the separation of the metals, at the same time increasing the 
density and consequent tenacity of the metal at the breech of the gun ; 
this dead-head is cut off before the gun is turned and bored. The metal 
is run into the mould at a temperature as near its point of solidification as 
possible, so as to diminish the chance of separation. The purest commer- 
cial qualities of copper and tin are always employed in gun metal. 

Bronze is essentially an alloy of copper and tin, containing more tin 
than gun metal ; its composition is varied according to its application, 
small quantities of zinc and lead being often added to it. Bronze is 
affected by changes of temperature, in a manner precisely the reverse of 
that in which steel is influenced, for it becomes hard and brittle when 
allowed to cool slowly, but soft and malleable when quickly cooled. 
The art of making bronze was practised before any progress had been 
made in working iron, and ancient weapons were very commonly of this 
material. 

Bronze coin (substituted for the copper coinage) is composed of 95- 
copper, 4 tin, and 1 zinc. 

Bell metal is an alloy of about 4 parts of copper and 1 of tin, to which 
lead and zinc are sometimes added. The metal of which musical instru- 
ments are made generally contains the same proportions of copper and tin 
as bell metal. 

Speculum metal, employed for reflectors in optical instruments, con- 
sists of 2 parts of copper and 1 of tin, to which a little zinc, arsenic, and 
silver are sometimes added to harden it and render it susceptible of a high 
polish. 

A superior kind of type metal is composed of 1 part of tin, 1 of anti- 
mony, and 2 of lead. 

Tin is not dissolved by nitric acid, but is converted into a white 
powder, the binoxide of tin ; hydrochloric acid dissolves it with the aid 
of heat, evolving hydrogen ; but the best solvent for tin is a mixture of 
hydrochloric with a little nitric acid. When the metal is acted upon by 
hydrochloric acid, it assumes a crystalline appearance, which has been 
turned to account for ornamenting tin-plate. If a piece of common tin- 
plate be rubbed over with tow dipped in a warm mixture of hydrochloric 
and nitric acids, its surface is very prettily diversified (moire metallique) ; 
it is usual to cover the surface with a coloured transparent varnish. 



STANNIC AND METASTANNIC ACIDS. . 383 

Commercial tin is liable to contain minute quantities of lead, iron, 
copper, arsenic, antimony, bismuth, gold, molybdenum, and tungsten. 
Pure tin may be precipitated in crystals by the feeble galvanic current 
excited by immersing a plate of tin in a strong solution of stannous 
chloride, covered with a layer of water, so that the metal may be in con- 
tact with both layers of liquid. 

281. Oxides of Tin. — Two oxides of this metal are known — the prot- 
oxide, SnO, and the binoxide, 8n0 2 . 

Protoxide of tin (SnO), or stannous oxide, is a substance of little prac- 
tical importance, obtained by decomposing stannous chloride with an 
alkali. Its colour varies, according to the mode of preparing it, from 
black or olive-coloured to red. It is a feebly basic oxide, and therefore 
dissolves in the acids ; it may also be dissolved by a strong solution of 
potash, but is then easily decomposed into metallic tin and the binoxide 
which combines with the potash. 

Binoxide of tin (Sn0 2 ) or stannic oxide, has been mentioned as the 
chief ore of tin, and is formed when tin is heated in air. Tin-stone, or 
cassiterite, as the natural form of this oxide is called, occurs in very hard, 
square prisms, usually coloured brown by peroxide of iron. In its insolu- 
bility in acids it resembles crystallised silica, and, like that substance, it 
forms, when fused with alkalies or their carbonates, compounds which are 
soluble in water ; these compounds are termed stannates, the binoxide of 
tin being known as stannic acid. 

Stannate of soda is prepared, on the large scale, for use as a mordant 
by calico-printers. The prepared tin ore (p. 379) is heated with solution 
of hydrate of soda, and boiled down till the temperature rises to 500° or 
600° F. ; or the tin ore is fused with nitrate of soda, when the nitric acid 
is expelled. It crystallises easily in hexagonal tables having the compo- 
sition Na 2 0.Sn0 2 , 4Aq., which dissolve easily in cold water, and are 
partly deposited again when the solution is heated. Most neutral salts of 
the alkalies also cause a separation of stannate of soda from its aqueous 
solution. The solution of stannate of soda has, like the silicate, a strong 
alkaline reaction, and when neutralised by an acid, yields a precipitate of 
hydrated stannic acid, H 2 O.Sn0 2 . If the solution of stannate of soda be 
added to an excess of hydrochloric acid, the stannic acid remains in solu- 
tion, and if the liquid be dialysed (see p. Ill), a jelly is first formed, which 
gradually liquefies as the chloride of sodium diffuses away, and eventually 
a pure aqueous solution of stannic acid is obtained, which is very easily 
gelatinised by the addition of a minute quantity of hydrochloric acid, or 
of some neutral salt. The great similarity between stannic and silicic 
acids is here Very remarkable. When heated, stannic acid is converted 
into metastannic acid. 

Metastannic acid (Sn 5 O 10 ) is obtained as a white crystalline hydrate when tin is 
oxidised by nitric acid ; when washed with water and dried by exposure to air, it has 
the composition Sn 5 O 10 .10H 2 O, but when dried at 212" F. it becomes Sn 5 O 10 .5H 2 O. 
If more strongly heated, it assumes a yellowish colour, and a hardness resembling 
that of powdered tin-stone. Putty powder, used for polishing, consists of meta- 
stannic acid ; as found in commerce it generally contains much oxide of lead. Meta- 
stannic acid is insoluble in water and diluted acids, and when fused with hydrated 
alkalies, is converted into a soluble stannate ; but if boiled with solution of potash it 
is dissolved in the form of metastannate of potash, which will not crystallise, like 
the stannate, but is obtained as a granular precipitate by dissolving hydrate of 
potash in its solution. This precipitate has the composition K 2 O.Sn 5 O 10 . 4Aq. ; it 
is very soluble in water, and is strongly alkaline. When it is heated to expel the 



384 STANNOUS AND STANNIC CHLORIDES. 

water, it is decomposed, and the potash may be washed out with water, leaving meta- 
stannic acid. The hydrated metastannic acid may be distinguished from hydrated 
stannic acid by the action of protochloride of tin, which converts it into the yellow 
metastannate of tin (SnO.Sn 5 O 10 .4Aq.). 

Stannate of tin is obtained as a yellowish hydrate by boiling protochloride of tin 
with hydrated sesquioxide of iron ; Fe 2 3 + 2SnCl 2 = SnO.Sn0 2 + 2FeCl 2 . It is 
sometimes written Sn 2 3 , and called sesquioxide of tin. 

282. Chlorides of tin. — The two chlorides of tin correspond in com- 
position to the oxides. 

Stannous chloride, or pi°otochloride of tin (SnCl. 2 ), is much used by dyers 
and calico-printers, and is prepared by dissolving tin in hydrochloric acid, 
when it is deposited, on cooling, in lustrous prismatic needles (SnCl 2 .2Aq.), 
known as tin crystals or salts of tin. The solution of the tin is generally 
effected in a copper vessel, in order to accelerate the action by forming 
a voltaic couple, of which the tin is the attacked metal. When gently 
heated, the crystals lose their water, and are partly decomposed, some 
hydrochloric acid being evolved (SnCl. 2 + H 2 = SnO + 2HC1) ; but, at a 
higher temperature, a great part of the chloride may be distilled in the 
anhydrous state ; the anhydrous chloride is generally prepared by distill- 
ing powdered tin with corrosive sublimate, when it remains in the retort 
as a brilliant grey solid, which requires a bright red heat to convert it into 
vapour. When water is poured upon the crystals of stannous chloride, they 
are only partially dissolved, a white oxy chloride of tin (SnCl 2 .Sn0.2Aq.) 
being separated. A moderately dilute solution of stannous chloride absorbs 
oxygen from the air, and deposits a white compound of perchloride and 
binoxide of tin ; 2SnCl 2 + 2 = SnCl 4 .Sn0 2 . If the solution contains 
much free hydrochloric acid it remains clear, being entirely converted into 
perchloride of tin. A strong solution of the chloride is not oxidised by 
the air, and the weak solution may be longer preserved in contact with 
metallic tin. Stannous chloride has a great attraction for chlorine as well 
as for oxygen, and is frequently employed as a deoxidising or dechlorinat- 
ing agent. Tin may be precipitated from stannous chloride by the action 
of zinc, in the form of minute crystals. A very beautiful tin tree is 
obtained by dissolving granulated tin in strong hydrochloric acid, with 
the aid of heat, in the proportion of 8 measured oz. of acid to 1000 grs. 
of tin, diluting the solution with four times its bulk of water, and intro- 
ducing a piece of zinc. 

Stannic chloride, or bichloride, or tetrachloride of tin (SnClJ, is ob- 
tained in solution when tin is heated with hydrochloric and nitric acids ; 
for the use of the dyer, the solution (nitromuriate of tin) is generally 
made with hydrochlorate of ammonia (sal-ammoniac) and nitric acid. The 
anhydrous perchloride is obtained by heating tin in a current of dry chlo- 
rine, when combination takes place with combustion, and the perchloride 
distils over as a heavy (sp. gr. 2*28) colourless liquid, volatile (boiling 
point, 240° F.), and giving suffocating white fumes in the air. When 
mixed with a little water, energetic combination takes place, and a 
crystalline hydrate (SnCl 4 .5Aq.) is formed, which is decomposed by an 
excess of water, with separation of hydrated stannic acid. Stannic 
chloride forms crystallisable double salts with the alkaline chlorides. Pink 
salt, used by dyers, is a compound of stannic chloride with hydrochlorate 
of ammonia 2(NH 3 .HCl).SnCl r 

283. Sulphides of tin. — The protosidphide, or stannous sulphide (SnS), 
is found in Cornwall as tin pyrites, and maybe easily prepared by heating 



TITANIUM. 385 

tin with sulphur, when it forms a grey crystalline mass. It is also 
obtained as a dark brown precipitate by the action of hydrosulphuric acid 
upon a solution of stannous chloride. Protosulphide of tin is a sulphur- 
base, but it may be dissolved by alkalies if some sulphur be added, which 
converts it into the bisulphide, a decided sulphur acid. 

Bisulphide of tin, or stannic sulphide (SnS 2 ), is commonly known as 
mosaic gold or bronze powder* and is used for decorative purposes. It is 
prepared by a curious process, which was devised in 1771, and must have 
been the result of a number of trials. 12 parts by weight of tin are dis- 
solved in 6 parts of mercury; the brittle amalgam thus obtained is 
powdered and mixed with 7 parts of sulphur and 6 of sal-ammoniac. 
The mixture is introduced into a Florence flask, which is gently heated 
in a sand-bath as long as any smell of hydrosulphuric acid is evolved ; 
the temperature is then raised to dull redness until no more fumes are 
disengaged. The mosaic gold is found in beautiful yellow scales at the 
bottom of the flask, and sulphide of mercury and calomel are deposited in 
the neck. The mercury appears to be used for effecting the fine division 
of the tin, and the sal-ammoniac to keep down the temperature (by its 
volatilisation) below the point at which the bisulphide of tin is converted 
into protosulphide. 

Mosaic gold, like gold itself, is not dissolved by hydrochloric or nitric 
acid, but easily by aqua regia. Alkalies also dissolve it when heated, 
since the bisulphide of tin is a sulphur acid. On adding hydrosulphuric 
acid to a solution of stannic chloride, the stannic sulphide is obtained 
as a yellow precipitate. 

284. Titanium (Ti = 50 parts by weight), which stands in close chemical relation- 
ship to tin, used to be described as a very rare metal, but it has lately been found to 
exist in considerable quantity in iron ores and clays, although no very important 
practical application has hitherto been found for it. The form in which it is gene- 
rally found is titanic acid (Ti0 2 ), which occurs uncombined in the minerals rutile, 
anatase, and brookite, the first of which is isomorphous with tin-stone, and is ex- 
tremely hard like that mineral. In combination with oxide of iron, titanic acid is 
found in iron-sand, iserine, or menachanite (found originally at Menachan in Corn- 
wall), which resembles gunpowder in appearance, and is now imported in abundance 
from Nova Scotia and New Zealand. Some specimens of this mineral contain 40 per 
cent, of titanic acid, combined with protoxide of iron. JTo extract titanic acid from 
it, the finely ground mineral is fused with three parts of carbonate of potash, when 
carbonic acid is expelled and titanate of potash formed ; on washing the mass with 
hot water, this salt is decomposed, a part of its alkali being removed by the water, 
and an acid titanate of potash left, mixed with the oxide of iron. This is dissolved 
in hydrochloric acid, and the solution evaporated to dryness, when the titanic acid, 
and any silicic acid which may be present, are converted into the insoluble modifica- 
tions, and are left on digesting the residue again with dilute hydrochloric acid ; the 
residue is washed with water (by decantation, for titanic acid easily passes through 
the filter), dried, and fused at a gentle heat with bisulphate of potash. The sul- 
phuric acid forms a soluble compound with the titanic acid (Ti0 2 .S0 3 ), which may 
te extracted by cold water, leaving the silicic acid undissolved. The solution con- 
taining the titanic acid is mixed with about twenty times its volume of water, and 
boiled for some time, when the titanic acid is separated as a white precipitate, 
exhibiting a great disposition to cling as a film to the surface of the flask in which 
the solution is boiled, and giving it the appearance of being corroded. The titanic 
acid becomes yellow when strongly heated, and white again on cooling ; it does 
not dissolve in solution of potash like silica, but when fused with potash it forms 
a titanate, which is decomposed by water ; the acid titanate of potash which is left 
may be dissolved in hydrochloric acid, and if the solution be neutralised with car- 
bonate of ammonia, hydrated titanic acid is precipitated, very much resembling 

* Bronze powder is also made by powdering finally laminated alloys of copper and zinc, 
a little oil being used to prevent oxidation. 

2 B 



386 TUNGSTEN. 

alumina in appearance. By dissolving the gelatinous hydrate in cold hydrochloric 
acid, and dialysing, a solution of titanic acid in water is obtained, which is liable to 
gelatinise spontaneously if it contain more than one per cent, of the acid. 

Titanic acid is employed in the manufacture of artificial teeth, and for imparting 
a straw-yellow tint to the glaze of porcelain. 

If a mixture of titanic acid and charcoal be heated to redness in a porcelain tube, 
through which dry chlorine is passed, tetrachloride of titanium (TiCl 4 ) is obtained 
as a colourless volatile liquid, very similar to perchloride of tin. By passing the 
vapour of the tetrachloride of titanium over heated sodium, the metallic titanium 
is obtained in prismatic crystals resembling specular iron ore in appearance. Like 
tin, it is said to dissolve in hydrochloric acid with liberation of hydrogen. The 
most remarkable chemical feature of titanium is its direct attraction for nitrogen, 
with which it combines when strongly heated jn air. By passing ammonia gas over 
titanic acid heated to redness, a violet powder is formed, which is a nitride of tita- 
nium (TiN 2 ). Beautiful cubes of a copper colour and great hardness, formerly be- 
lieved to be metallic titanium, are found adhering to the slags of blast-furnaces in 
which titaniferous iron ores are smelted ; these contain about 77 per cent, of tita- 
nium, 18 of nitrogen, and rather less than 4 of carbon, and are believed to consist of 
a compound of cyanide with nitride of titanium, TiCy 2 . 3Ti 3 N 2 . A similar compound 
is obtained by passing nitrogen over a mixture of titanic acid and charcoal heated to 
whiteness. 

Yiolet-coloured crystals of terchloride of titanium (TiCl 3 ), are obtained by passing 
hydrogen charged with vapour of tetrachloride of titanium through a red-hot porcelain 
tube ; it forms a violet solution in water, which resembles stannous chloride in its 
reducing properties. 

When a solution of titanic acid (or acid titanate of potash) in hydrochloric acid is 
acted on by zinc, a violet solution is formed, which deposits, after a time, a blue (or 
green) precipitate, which appears to be a sesquioxide of titanium (Ti 2 3 ), and rapidly 
absorbs oxygen from the air, being converted into titanic acid. A protoxide of tita,- 
nium (TiO) is said to be obtained as a black powder when titanic acid is strongly heated 
in a crucible lined with charcoal. 

Bisulphide of titanium is not precipitated, like bisulphide of tin, when hydrosul- 
phuric acid acts upon the tetrachloride; but if a mixture of the vapour of tetrachloride 
of titanium with hydrosulphuric acid is passed through a red-hot tube, greenish-yel- 
low scales of the bisulphide, resembling mosaic gold, are deposited. 

Titanium, like tin, is classed among the tretratomic elements. 

285. Tungsten (W= 184) is chiefly found in the mineral wolfram, which occurs, 
often associated with tin-stone, in large brown shining prismatic crystals, which are 
even heavier than tin-stone (sp. gr. 7*3), from which circumstance the metal derives its 
name, tungsten, in Swedish, meaning heavy stone. The symbol (W) used for tung- 
sten is derived from the Latin name wolframium. "Wolfram contains the tungstates 
of iron and manganese in somewhat variable proportions, but its general composition 
is expressed by the formula ,MnO.W0 3 .3(FeO. W0 3 ). Scheelite, tungstate of lime 
(CaO. W0 3 ), is another mineral in which tungsten is found. A tungstate of copper 
has been found in Chili. 

Tungstate of soda is employed by calico-printers as a mordant, and is sometimes ap- 
plied to muslin, in order to render it uninflammable. It is obtained by fusing wolfram 
with carbonate of soda, an operation to which tin ores containing this mineral in 
large quantity are sometimes submitted previously to smelting them. Water extracts 
the tungstate of soda, which may be crystallised in rhomboidal plates having the 
composition Na 2 0. W0 3 , 2Aq. When a solution of this salt is mixed with an excess 
of hydrochloric acid, white hydrated tungstic acid (H 2 O.W0 3 .Aq.) is precipitated; 
but if dilute hydrochloric acid be carefully added to a 5 per cent, solution of tung- 
state of soda, in sufficient proportion to neutralise the alkali, and the solution be then 
dialysed (p. Ill), the chloride of sodium passes through, and a pure aqueous solution 
of tungstic acid is left in the dialyser. This solution is unchanged by boiling, and 
when evaporated to dryness, it forms vitreous scales, like gelatine, which adhere very 
strongly to the dish. It redissolves in one-fourth of its weight of water, forming a 
solution of the very high specific gravity 3 *2, which is, therefore, able to float glass. 
The solution has a bitter and astringent taste, and decomposes carbonate of soda with 
effervescence. It becomes green when exposed to air, from the deoxidising action of 
organic dust. When the hydrated tungstic acid is heated, it loses water, and be- 
comes of a straw-yellow colour and insoluble in acids. There are at least two modi- 
fications of tungstic acid, which bear to each other a relation similar to that between 
stannic and metastannic acids. 



MOLYBDENUM. 387 

Tungstate of baryta has been employed as a substitute for white lead in painting. 

The most characteristic property of tungstic acid is that of yielding a blue oxide 
( W0 2 . W0 3 ), when placed in contact with hydrochloric acid and metallic zinc. 

.A very remarkable compound containing tungstic acid and soda is obtained when 
bitungstate of soda (Na 2 0.2W0 3 .4H 2 0) is fused with tin. If the fused mass be 
treated with strong potash, to remove free tungstic acid, washed with water, and 
treated with hydrochloric acid, yellow lustrous cubical crystals are obtained, which 
are remarkable, among sodium compounds, for their resistance to the action of water, 
of alkalies, and of all acids except hydrofluoric. The composition of these crystals 
appears to be Na 2 O.W0 2 .2W0 3 . 

The binoxide of tungsten (W0 2 ) appears to be an indifferent oxide, and is obtained 
by reducing tungstic acid with hydrogen at a low red heat, when it forms a brown 
powder which is dissolved by boiling in solution of potash, hydrogen being evolved, 
and tungstate of potash formed. 

Metallic tungsten is obtained by reducing tungstic acid with charcoal at a white 
heat, as an iron-grey infusible metal of sp. gr. 17 '6, very hard, not affected by hydro- 
chloric or diluted sulphuric acid, but converted into tungstic acid by the action of 
nitric acid. When tungsten is dissolved in about ten times its weight of fused steel, 
it forms an extremely hard alloy. 

"When tungsten is heated in chlorine, the tungstic chloride (WC1 6 ) sublimes in 
bronze coloured needles, which are decomposed by water. When gently heated in 
hydrogen, it is converted into the tetrachloride (WC1 4 ), but if its vapour be mixed 
with hydrogen and passed through a glass tube heated to redness, metallic tungsten is 
obtained in a form in which it is not dissolved even by aqua regia, though it may be con- 
verted into tungstate of potash by hypochlorite of potash mixed with potash in excess. 

Bisulphide of tungsten (WS 2 ) is a black crystalline substance resembling plumbago, 
obtained by heating a mixture of bitungstate of potash with sulphur, and. washing 
with hot water. Tersulphide of tungsten (WS 3 ) is a sulphur -acid, obtainable as a 
brown precipitate by dissolving tungstic acid in an alkaline sulphide, and precipi- 
tating by an acid. 

286. Molybdenum (Mo = 96) derives its name from (Aokvf&oavu, lead, on account 
of the resemblance of its chief ore, molybdena, to black lead. Molybdena is the bisul- 
phide of molybdenum (MoS 2 ), and is found chiefly in Bohemia and Sweden ; it may 
be recognised by its remarkable similarity to plumbago, and by its giving a blue solu- 
tion when boiled with strong sulphuric acid. It is chiefly employed for the prepara- 
tion of molybdate of ammonia, which is used in testing for phosphoric acid. For this 
purpose the bisulphide of molybdenum is roasted in air at a dull red heat, when 
sulphurous acid is evolved, and molybdic acid (Mo0 3 ) mixed with oxide of iron is left. 
The residue is digested with strong ammonia, which dissolves the molybdic acid in 
the form of molybdate of ammonia, obtainable in prismatic crystals on evaporation. 
When a solution of molybdate of ammonia is added to a phosphate dissolved in 
diluted nitric acid, a yellow precipitate of phosphomolybdate of ammonia is produced, 
which contains molybdic and phosphoric acids combined with ammonia, by the for- 
mation of which very minute quantities of phosphoric acid can be detected. If 
hydrochloric acid be added in small quantity to a strong solution of molybdate of 
ammonia, the molybdic acid is precipitated, but it is dissolved by an excess of 
hydrochloric acid, and if the solution be dialysed, the molybdic acid is obtained in 
the form of an aqueous solution which reddens blue litmus, has an astringent taste, 
and leaves a soluble gum-like residue when evaporated. Molybdic acid _fuses_ at; a 
red heat to a yellow glass, and may be sublimed in a current of air in shining 
needles. In contact with diluted hydrochloric acid and metallic zinc, it is con- 
verted into a blue compound of molybdic acid with binoxide of molybdenum 
(Mo0 2 .4Mo0 3 ) which is soluble in water, but is precipitated on adding a saline 
solution. Molybdate of lead (PbO.Mo0 3 ) is found as a yellow crystalline mineral. 
The binoxide of molybdenum (Mo0 2 ) is basic, and forms dark red-brown salts. Prot- 
oxide of molybdenum (MoO) is obtained by adding an alkali to the solution resulting 
from the prolonged action of zinc upon a hydrochloric solution of molybdic acid. It 
is a basic oxide which absorbs oxygen from the air. 

Metallic molybdenum is obtained by reducing molybdic acid with charcoal at a 
white heat, as a white metal, fusible with difficulty, unacted upon by hydrochloric and 
diluted sulphuric acids, but converted into molybdic acid by boiling with nitric acid. 
It is rather a light metal, its specific gravity being 8 '62. When heated in chlorine 
it yields tetrachloride of molybdenum (MoCl 4 ), which forms a red vapour, and condenses 
in crystals resembling iodine, soluble in water. A bichloride (MoCl 2 ) is also known. 
The tersulphide (MoS 3 ) and tetrasulphide (MoS 4 ) of molybdenum are sulphur-acids. 



388 VANADIUM — PLATINUM. 

In addition to the natural sources of molybdenum above mentioned, there may be 
noticed molybdic ochre (an impure molybdic acid), and the difficultly fusible masses 
called bear, from the copper works in Saxony, which contain a large amount of 
molybdenum combined with iron, copper, cobalt, and nickel. 

287. Vanadium* (V = 51 *3) was originally discovered in certain Swedish iron ores, 
but its chief ore is the vanadiate of lead, which is found in Scotland, Mexico, and 
Chili. Vanadic acid has also been found in some clays, in the cupriferous sandstone 
at Perm in Russia, and Alderley Edge in Cheshire. By treating the vanadiate of 
lead with nitric acid, expelling the excess of acid by evaporation, and washing out 
the nitrate of lead with water, impure vanadic acid (V 2 5 ) is obtained, which may 
be purified by dissolving in ammonia, crystallising the vanadiate of ammonia, and 
decomposing it by heat, when vanadic acid is left as a reddish-yellow fusible solid, 
which crystallises on cooling, and dissolves sparingly in water, giving a yellow solu- 
tion. It dissolves in hydrochloric acid, and if the solution be treated with a reducing 
agent (such as hydrosulphuric acid) it assumes a fine blue colour. If a solution of 
vanadiate of ammonia be mixed with tincture of galls, it gives an intensely black 
fluid, which forms an excellent ink, for it is not bleached by acids (which turn it 
blue), alkalies, or chlorine. 

Vanadium itself has not been obtained. Berzelius endeavoured to procure it by 
heating vanadic acid with potassium, but Roscoe, who has carefully investigated the 
vanadium compounds, has shown that the apparently metallic powder thus obtained 
is really an oxide (V 2 2 ). 

The oxides of vanadium correspond in composition to those of nitrogen (omitting 
N 2 0). V 2 2 is a basic oxide, forming salts which give lavender- coloured solutions ; 
these absorb oxygen rapidly from the air, and act as powerful reducing agents. 
V 2 3 is a black crystalline body resembling plumbago, and capable of conducting 
electricity, obtained by heating vanadic acid in a current of hydrogen ; it is a basic 
oxide. V 2 4 is produced when V 2 3 is heated in air ; it also plays the part of a base, 
yielding blue salts. Vanadic acid, V 2 5 , forms purple and green compounds with the 
above oxides. The yellow fuming liquid formerly called chloride of vanadium is 
really an oxychloride VOCl 3 , The oxychiorides V 2 2 C1, VOC1, and VOCl 2 , have also 
been obtained. There are two compounds of vanadium with nitrogen, VN and VN 2 . 
It will be remarked that the composition of the compounds of vanadium connects this 
metal with nitrogen, phosphorus, and arsenic. 

288. Niobium (Nb =94) (formerly called columbium) has been obtained from a rare 
dark grey hard crystalline mineral known as columbite, occurring in Massachusetts. 
This mineral contains niobic acid (Nb0 2 ) combined with the oxides of iron and 
manganese. 

The niobic acid is extracted by a laborious process, and forms a white powder spar- 
ingly soluble in hydrochloric acid. Niobium itself has been obtained as a black 
powder insoluble in nitric acid and in aqua regia, but dissolved by a mixture of nitric 
and hydrofluoric acids. 

Tantalum, formerly believed to be identical with niobium, occurs in the tantalite 
and yttrotantalite of Sweden, which contain tantalic acid (Ta0 2 )t resembling niobic 
acid. 

Niobium and tantalum have recently been found to the amount of 2 or 3 per cent, 
in the tin ore of Montebras. 

PLATINUM. 

Pt = 197*1 parts by weight. 

289. Platinum (platina, Spanish diminutive of silver) is always found 
in the metallic state, distributed in flattened grains through alluvial 
deposits similar to those in which gold is found ; indeed, these grains are 
generally accompanied by grains of gold, and of sl group of very rare 
metals only found in platinum ores, viz., palladium, iridium, osmium, 
rhodium, and ruthenium. Eussia furnishes the largest supply of platinum 
from the Ural Mountains, but smaller quantities are obtained from Brazil, 
Peru, Borneo, Australia, and California. 

The process for obtaining the platinum in a marketable form is rather 

* Vanadis, a Scandinavian deity. 

+ Ta 2 O s , according to more recent experiments. 



PROPERTIES OF PLATINUM. 389 

a chemical than a metallurgic operation. The ore, containing the grains 
of platinum and the associated metals, is heated with a dilute mixture of 
hydrochloric and nitric acids, by which the platinum is converted into 
perchloride of platinum (PtCLJ and dissolved, whilst the iridium and 
osmium are left in the residue. The solution is then mixed with some chlo- 
ride of ammonium, which combines with the perchloride of platinum to form 
a yellow insoluble salt (ammonio-chloride of platinum, 2(NH 3 .HCl).PtCl 4 ). 
This precipitate is collected, washed, and heated to redness, when all its 
constituents, except the platinum, are expelled in the form of gas, that 
metal being left in the peculiar-porous condition in which it is known as 
spongy platinum. To convert this into compact platinum is by no means 
an easy task, on account of the infusibility of the metal, for it remains 
solid at the very highest temperatures of our furnaces. The spongy 
platinum is finely powdered in a wooden mortar (as it would cohere into 
metallic spangles in one of a harder material) and rubbed to a paste with 
water ; this paste is then rubbed through a sieve to render it perfectly 
smooth and uniform, and introduced into a cylinder of brass, in which it 
is subjected to pressure so as to squeeze out the water and cause the 
minute particles of platinum to cohere into a somewhat compact disk ; 
this disk is then heated to whiteness and beaten into a compact metallic 
ingot by a heavy hammer ; it is then ready for forging. 

A more modern process for obtaining platinum from its ores is based 
upon the tendency of this metal to dissolve in melted lead. The platinum 
ore is fused in a small reverberatory furnace, with an equal weight of sul- 
phide of lead and the same quantity of oxide of lead, when the sulphur 
and oxygen escape as sulphurous acid, and the reduced lead dissolves the 
platinum, leaving undissolved a very heavy alloy of osmium and iridium 
which sinks to the bottom. The upper part of the alloy of lead and 
platinum is then ladled out and cupelled (page 351), when the latter metal 
is left in a spongy condition, the lead being removed in the form of 
oxide. The platinum is then fused by the aid of the oxyhydrogen blow- 
pipe, in a furnace made of lime (fig. 276), whence it is poured into an 
ingot mould made of gas-carbon. The melted platinum absorbs oxygen 
mechanically like melted silver, and evolves it again on cooling (see page 
352). Platinum articles are now frequently made from the fused metal, 
instead of from that which has been welded. 

Its resistance to the action of high temperatures and of most chemical 
agents, renders platinum of the greatest service in chemical operations. 
It will be remembered that platinum stills 
are employed, even on the large scale, for the 
concentration of sulphuric acid. In the form 
of basins, small crucibles, foil, and wire, this 
metal is indispensable to the analytical che- 
mist. Unfortunately, it is softer than silver, 
and therefore ill adapted for wear, and is so 
heavy (sp. gr. 21 -5) that even small vessels 
must be made very thin in order not to be 
too heavy for a delicate balance. Since it 
expands less than any other metal when 

heated, wires of platinum maybe sealed into " ■ •'"""""""''■'"' "'"— 

glass without danger of splitting it by un- Fi 275 

equal expansion. Its malleability and duc- 
tility are very considerable, so that it is easily rolled into thin foil and 




390 PROPERTIES OF PLATINUM. 

drawn into fine wires ; in ductility it is surpassed only by gold and silver, 
and it has been drawn, by an ingenious contrivance of Wollaston's, into 
wire of only g^^^tli of an inch in diameter, a mile of which (notwith- 
standing the high specific gravity of the metal) would only weigh a single 
grain. This remarkable extension of the metal was effected by casting a 
cylinder of silver around a very thin platinum wire obtained by the ordi- 
nary process of wire-drawing ; when the cylinder of silver, with the 
platinum wire in its centre, was itself drawn out into an extremely thin 
wire, of course the platinum core would have become inconceivably thin, 
and when the silver casing was dissolved off by nitric acid, this minute 
filament of platinum was left. Platinum is sometimes employed for the 
touch-holes of fowling-pieces on account of its resistance to corrosion. 
A little iridium is sometimes added to platinum in order to increase its 
elasticity. 

The remarkable power possessed by platinum, of inducing chemical 
combination between oxygen and other gases, has already been noticed. 
Even the compact metal possesses this property, as may be seen by heat- 
ing a piece of platinum foil to redness in the name of a gauze gas-burner, 
rapidly extinguishing the gas, and turning it on again, when the cold 
stream of gas will still maintain the metal at a red heat, in consequence of 
the combination with atmospheric oxygen at the surface of the platinum. 
A similar experiment may be made by suspending a coil of platinum 
wire in the flame of a spirit-lamp (fig. 277), and suddenly 
blowing out the flame when the metal is intensely heated ; 
the wire will continue to glow by inducing the combina- 
tion of the spirit vapour with oxygen on its surface. By 
substituting a little ball of spongy platinum for the coil 
of platinum wire, and mixing some fragrant essential oil 
with the spirit, an elegant perfuming lamp has been con- 
trived. Upon the same principle an instantaneous light 
apparatus has been made, in which a jet of hydrogen gas 
lg ' ' is kindled by falling upon a fragment of cold spongy 

platinum, which at once ignites it by inducing its combination with the 
oxygen condensed within the pores of the metal. Spongy platinum is 
obtained in a very active form by heating the ammonio-chloride of pla- 
tinum very gently in a stream of coal-gas or hydrogen as long as any 
fumes of hydrochloric acid are evolved. 

If platinum be precipitated in the metallic state from a solution, it is 
obtained in the form of a sooty powder, called platinum-black, which 
possesses this power of promoting combination with oxygen in the highest- 
perfection. This form of platinum may be obtained by dissolving the 
metal in aqua regia, which converts it into perchloride of platinum (PtCl 4 ), 
evaporating the solution to dryness, and heating the residue gently on a 
sand-bath as long as it smells strongly of chlorine. The chloride of plati- 
num (PtCl 2 ) thus obtained is dissolved in a strong solution of potash 
and heated with alcohol, when the platinum-black is precipitated, and 
must be filtered off, washed, and dried at a gentle heat. 

Platinum in this form is capable of absorbing 800 times its volume of 
oxygen, which does not enter into combination with it, but is simply 
condensed into its pores, and is available for combination with other 
bodies. A jet of hydrogen allowed to pass on to a grain or two of this 
powder is kindled at once, and if a few particles of it be thrown into a 
mixture of hydrogen and oxygen, explosion immediately follows. A drop 




OXIDES AND CHLOEIDES OF PLATINUM. 391 

of alcohol is also inflamed when allowed to fall upon a little of the powder. 
Platinum black loses its activity after having been heated to redness. 

Although platinum resists the action of hydrochloric and nitric acids, 
unless they are mixed, and is unaffected at the ordinary temperature by 
other chemical agents, it is easily attacked at high temperatures by phos- 
phorus, arsenic, carbon, boron, silicon, and by a large number of the 
metals ; the caustic alkalies and alkaline earths also corrode it, so that 
some discretion is necessary in the use of vessels made of this costly 
metal. When platinum is alloyed with 10 parts of silver, both metals 
may be dissolved by nitric acid. 

290. Oxides of platinum. — Only one compound of platinum with 
oxygen is known in the separate state, the other having been obtained 
in combination with water. The protoxide, PtO (platinous oxide), is 
precipitated as a black hydrate by decomposing the protochloride with 
potash, and neutralising the solution with dilute sulphuric acid. It is 
a feeble base, and decomposes when heated, leaving metallic platinum. 
Binoxide of platinum, Pt0 2 (platinic oxide), is also a weak base, but 
occasionally plays the part of an acid, whence it is sometimes termed 
platinic acid. Platinate of soda (Na 2 0.3Pt0 2 .6Aq.) may be crystallised 
from a solution of the hydrated binoxide in soda. Platinate of lime is 
convenient for the separation of platinum from iridium, which is gene- 
rally contained in the commercial metal ; for this purpose the platinum 
is dissolved in nitro-hydro chloric acid, the solution evaporated till it 
solidifies on cooling, the mixed chlorides of iridium and platinum dis- 
solved in water, and decomposed with an excess of lime without exposure 
to light; the platinum then passes into solution as platinate of lime, and 
the platinic acid may be separated from the filtered solution, though still 
in combination with lime, by exposure to light. Acids dissolve binoxide 
of platinum, forming salts of a brown colour which have not been crys- 
tallised. If binoxide of platinum be dissolved in diluted sulphuric acid 
and the solution mixed with excess of ammonia, a black precipitate of 
fulminating platinum is obtained, which detonates violently at about 
400° P. This compound is said to have a composition corresponding to 
the formula N 2 H 2 Pt iv .4H 2 0, or a combination of water with a double 
molecule of ammonia (N 2 H 6 ), in which four atoms of hydrogen are replaced 
by one atom of tetratomic platinum. 

Chlorides of platinum. — The perchloride, or platinic chloride (PtCl 4 ), is 
the most useful salt of the metal, and may be prepared by dissolving 
scraps of platinum foil in a mixture of four measures of hydrochloric acid 
with one of nitric acid (100 grains of platinum require 2 measured ounces 
of hydrochloric acid), evaporating the liquid at a gentle heat to the con- 
sistence of a syrup, redissolving in hydrochloric acid, and again evapo- 
rating to expel excess of nitric acid. The syrupy liquid solidifies on 
cooling to a red-brown mass, which is very deliquescent, and dissolves 
easily in water or alcohol to a red-brown solution. If the concentrated 
solution be allowed to cool before all the free hydrochloric acid has been 
expelled, long brown prismatic crystals of a combination of the perchloride 
with hydrochloric acid are obtained (PtCl 4 .2HC1.6Aq.) The perchloride 
of platinum is remarkable for its disposition to form sparingly soluble 
double chlorides with the chlorides of the alkali metals and the hydro- 
chlorates of organic bases, a property of great value to the chemist in 
effecting the detection and separation of these bodies. 



392 PROTOCHLORIDE OF PLATINUM. 

A good example of this has lately been afforded in the separation 
of potassium, rubidium, and ccesium. The chlorides of these three 
metals having been separated from the various other salts contained in 
the mineral water in which they occur, are precipitated with perchlo- 
ride of platinum, which forms combinations with all the three chlorides. 
The platino-chloride of potassium is more easily dissolved by boiling 
water than those of rubidium and ccesium, and is removed by boiling the 
mixed precipitate with small portions of water as long as the latter 
acquires a yellow colour. The remaining platino-chlorides of rubidium 
and ccesium are then heated in a current of hydrogen, which reduces the 
platinum to the metallic state, and the chlorides may then be extracted 
by water, in which they are very soluble. 

Platino-chloride of potassium (2KCl,PtCl 4 ) forms minute yellow octa- 
hedral crystals ; those of rubidium and ccesium have a similar composition 
and crystalline form. 

Platino-chloride of sodium differs from these in being very soluble in 
water and alcohol; it may be crystallised in long red prisms, having 
the composition (2NaCl,PtCl 4 ,6Aq.) 

Ammonio-chloride of platinum (2NH 3 .HCl).PtCl 4 ) has been already 
noticed as the form in which platinum is precipitated in order to sepa- 
rate it from other metals. It crystallises, like the potassium-salt, in 
yellow octahedra, which are very sparingly soluble in water and insoluble 
in alcohol. It is the form into which nitrogen is finally converted in 
analysis in order to determine its weight. When heated to redness, this 
salt leaves a residue of spongy platinum. The perchloride of platinum is 
sometimes used for browning gun-barrels, &c, under the name of muriate 
of platina. 

Protochloride of platinum or platinous chloride (PtCl 2 ). — The perchloride of platinum 
may be heated to 450° F. without decomposition, but above that temperature it 
evolves chlorine, and is slowly converted into the protochloride, which is reduced, at 
a much higher temperature, to the metallic state. Platinous chloride forms a dingy 
green powder, which is insoluble in water and in nitric and sulphuric acids, but 
dissolves in hot hydrochloric acid, and in solution of platinic chloride, yielding in 
the former a bright red, in the latter a very dark brown-red solution. Its solution 
in hydrochloric acid is not precipitated by chloride of potassium, but a soluble 
double chloride (2KCl,PtCl 2 ) may be crystallised from the liquid. If hydrochlorate 
of ammonia be added to the hydrochloric solution, a double salt of hydrochlorate of 
ammonia with protochloride of platinum 2(NH 3 .HCl).PtCl 2 ) may be obtained in 
yellow crystals by evaporation. If, instead of hydrochlorate of ammonia, free 
ammonia be added in excess to the boiling solution of protochloride of platinum in 
hydrochloric acid, brilliant green needles (green salt of Magnus) are deposited on 
cooling, which contain the elements of platinous chloride and ammonia (PtCl 2 (NH 3 ) 2 ,- 
but from the behaviour of this compound with chemical agents, its true formula 
would appear to be N 2 H 6 Pt"Cl 2 , in which the place of two atoms of hydrogen in two 
molecules of sal-ammoniac is occupied by platinum. By heating this salt with an 
excess of ammonia, the solution, on cooling, deposits yellowish-white prismatic crys- 
tals of hydrochlorate of diplatosamine ; N 4 H 10 Pt".2HCl.Aq., the production of which 
may be represented by the equation — 

N 2 H 6 Pt"Cl 2 + 2NH 3 = N 4 H 10 Pt".2HCl. 

By decomposing a solution of this salt with sulphate of silver, the sulphate of dipla- 
tosamine is obtained ; N 4 H 10 Pt".2HCl + Ag 2 O.S0 3 = N 4 H 10 Pt".H 2 O.SO 3 + 2AgCl. 
When the solution of sulphate of diplatosamine is treated with hydrate of baryta, 
sulphate of baryta is precipitated, and a powerfully alkaline solution is obtained, 
which yields crystals of hydrate of diplatosamine N 4 H I0 Pt".2H 2 O, a strong alkali 
which may be regarded as a compound of water with 4 molecules of ammonia (N 4 H 12 ), 
in which 2 atoms of hydrogen are replaced by platinum. The hydrate of diplatosa- 
mine has a strong resemblance to the hydrated. mineral alkalies, eagerly absorbing 



PALLADIUM. 393 

carbonic acid from the air, and expelling ammonia from its salts. "When the 
hydrate of diplatosamine is heated to 230° F. it gives off water and ammonia, and 
becomes converted into a grey insoluble substance, which is hydrate of platosamine, 
N 2 H 4 Pt".H 2 0, and may be regarded as a compound of water with a double molecule 
of ammonia (N 2 H 6 ), in which one-third of the hydrogen is replaced by platinum. 
This substance is also a base, and forms salts, most of which are insoluble ; the 
sulphate of platosamine, N 2 H 4 Pt.H 2 O.S0 3 .Aq., may be regarded as sulphate of 
ammonia (2NH 3 .H 2 O.S0 3 ), in which two atoms of the hydrogen are replaced by 
platinum. The hydrochlorate of platosamine (N 2 H 4 Pt.2HCl) is isomeric with the 
green salt of Magnus, and may be obtained from that compound by dissolving it in 
a hot solution of sulphate of ammonia, from which it crystallises on cooling.* 

If the hydrochlorate of platosamine, suspended in boiling water, be treated with 
chlorine, it is converted into hydrochlorate of platinamine, N 2 H 2 Pt iv .4HCl, which 
may be represented as the hydrochlorate of an ammonia, in which 4 atoms of 
hydrogen have been replaced by 1 atom of platinum in the condition in which it 
exists in the perchloride (PtCl 4 ), where it is equivalent to H 4 . _ The conversion of the 
hydrochlorate of platosamine into hydrochlorate of platinamine may be represented 
by the equation, N 2 H 4 Pt.2HCl + Cl 2 = N 2 H 2 Pt.4HCl. By boiling the hydro- 
chlorate of platinamine with nitrate of silver, it is converted into nitrate of platina- 
mine N 2 H 2 Pt(HISr0 3 ) 4 , and when this is dissolved in boiling water and decomposed 
by ammonia, the hydrate of platinamine (N 2 H 2 Pt,4H 2 0) is obtained in yellow pris- 
matic crystals, having the same composition as that assigned to fulminating platinum. 

Several other platinum compounds derived from ammonia have been obtained, 
but cannot at present be so conveniently classified. The following table exhibits 
the composition of those here enumerated, the platinum, as it exists in platinous 
chloride (PtCl 2 ), occupying the place of 2 atoms of hydrogen, being represented by 
Pt", and the platinum, as it exists in platinic chloride (PtCl 4 ) occupying the place of 
4 atoms of hydrogen, by Pt Iv . 



Hydrate of platosamine, . 
Hydrochlorate of platosamine, . 
Sulphate of platosamine, . 


F 2 H 4 Pt".H 2 

N 2 H 4 Pt".2HCl 

N 2 H 4 Pt".H 2 O.S0 3 .Aq 


Hydrate of platinamine, . 
Hydrochlorate of platinamine, . 


F 2 H 2 Pt Iv .4H 2 
N 2 H 2 Pt 1 \4HCl 


Hydrate of diplatosamine, 
Hydrochlorate of diplatosamine, 
Sulphate of diplatosamine, 


N 4 H 10 Pt".2H 9 O 

N 4 H 10 Pt".2HCl.Aq. 

N 4 H 10 Pt".H 2 O.SO 3 . 



' Some of the salts of diplatinamine (N 4 H 8 Pt IV ) have been obtained, this base being 
derived from 4 molecules of ammonia in which H 4 have been replaced by Pt IV . 

The sulphides of platinum correspond in composition to the oxides and chlorides, 
and may be obtained by the action of hydrosulphuric acid upon the respective chlo- 
rides, as black precipitates. 

291. Palladium (Pd = 106*5) is found in small quantity associated with native 
gold and platinum. It presents a great general resemblance to platinum, but is dis- 
tinguished from it by being far more easily oxidised, and by its special attraction for 
cyanogen, with which it forms an insoluble compound. This circumstance is taken 
advantage of in separating palladium from the platinum ores, for which purpose the 
solution from which the greater part of the platinum has been precipitated by hydro- 
chlorate of ammonia (p. 389) is neutralised with carbonate of soda, and mixed with 
solution of cyanide of mercury Hg(CN) 2 , when a yellowish precipitate of cyanide of 
palladium is obtained, yielding spongy palladium when heated, which may be welded 
into a compact form in the same manner as platinum. When alloyed with native 
gold, palladium is separated by fusing the alloy with silver, and boiling it with nitric 
acid, which leaves the gold undissolved. The silver is precipitated from the solu- 
tion as chloride by adding chloride of sodium, and metallic zinc is placed in the 
liquid, which precipitates the palladium, lead, and copper, as a black powder. This 
is dissolved in nitric acid, and the solution mixed with an excess of ammonia, which 
precipitates the oxide of lead, leaving the copper and palladium in solution. On 
adding hydrochloric acid in slight excess, a yellow precipitate of hydrochlorate of 

* The salts of diplatosamine are distinguished from those of platosamine by the action 
of nitrous acid, which gives a fine blue or green precipitate or coloration with the former. 

For the cause of this change, and for many other interesting points in the history of 
these platinum compounds, the reader is referred to the elaborate and accurate memoir by 
Hadow (Journal of the Chemical Society, August 1866). 



394 RHODIUM — OSMIUM. 

palladamine (N 2 H 4 Pd,2HCl) is obtained, which leaves metallic palladium when 
heated. 

Palladium is harder than platinum and much lighter (sp. gr. 11'5) ; it is malleable 
and ductile like that metal, and somewhat more fusible, though it cannot be melted 
in an ordinary furnace.* It is unchangeable in air unless heated, when it becomes 
blue from superficial oxidation, but regains its whiteness when further heated, the 
oxide being decomposed. Unlike platinum, it may be dissolved by nitric acid, form- 
ing nitrate of palladium (PdO.N 2 5 ), which is sometimes employed in analysis for 
precipitating iodine from the iodides, in the form of black iodide of palladium (Pdl 2 ). 
Palladium is useful, on account of its hardness, lightness, and resistance to tarnish, 
in the construction of philosophical instruments ; alloyed with twice its weight of 
silver, it is used for small weights. 

Of the oxides of palladium, two correspond with those of platinum, and a basic 
oxide (PdO) has been obtained by gently heating the binoxide. Tetrachloride of 
p)alladium (PdCl 4 ) is very unstable, being easily decomposed, even in solution, into 
the bichloride (PdCJ 2 ) and free chlorine. Both the chlorides form double salts with 
the alkaline chlorides, those containing the palladious chloride (PdCl 2 ) having a dark 
green colour. Pulverulent carbide of palladium is formed when the metal is heated 
in the flame of a spirit-lamp. 

292. Rhodium (Ro = 104 -3), another of the metals associated with the ores of 
platinum, has acquired its name from the red colour of many of its salts {pohov, a rose). 
It is obtained from the solution of the ore in aqua regia by precipitating the platinum 
with hydrochlorate of ammonia, neutralising with carbonate of soda, adding cyanide 
of mercury to separate the palladium, and evaporating the filtered solution to dryness 
with excess of hydrochloric acid. On treating the residue with alcohol, the double 
chloride of rhodium and sodium is left undissolved as a red powder. By heating this 
in a tube through which hydrogen is passed, the rhodium is reduced to the metallic 
state, and the chloride of sodium may be washed out with water, leaving a grey 
powder of metallic rhodium, which is fused by the oxyhydrogen blowpipe with 
greater difficulty than platinum, and forms a very hard malleable metal not dissolved 
even by aqua regia, although this acid dissolves it in the ores of platinum, because it 
is alloyed with other metals. If platinum be alloyed with 30 per cent, of rhodium, 
however, it is not affected by aqua regia, which will probably render the alloy useful 
for chemical vessels. Rhodium may be brought into solution by fusing it with bisul- 
phate of potash, when sulphurous acid escapes, and a double sulphate of rhodium and 
potash is formed, which gives a pink solution. with water. Finely divided rhodium 
is oxidised when heated in air. It appears to form two oxides, the protoxide (RoO), 
which is very little known, and the sesquioxide (Ro 2 3 ), obtained by fusing rhodium 
with carbonate of potash and nitre, and washing the fused mass with water, which 
leaves an insoluble compound of the sesquioxide with potash ; on treating this with 
hydrochloric acid, the sesquioxide of rhodium is left. It is not decomposed by heat, 
and is insoluble in acids, though it is a basic oxide, and its salts, which have a red 
colour, are obtained by indirect methods. 

Terchloride of rhodium (RoCl 3 ) has a brownish black colour, and does not crystal- 
lise. Its aqueous solution is red, and it forms cry stalli sable double salts with the 
alkaline chlorides, which have a fine red colour. _ The double chloride of rhodium 
and sodium, (3XaCl.RoCl 3 ).9Aq., is prepared by heating a mixture of pulverulent 
rhodium and chloride of sodium in a current of chlorine. It crystallises in red 
octahedra. On boiling a solution of terchloride of rhodium with ammonia in excess, 
a yellow ammoniated salt (RoCl 3 .5NH 3 ) maybe crystallised out, from which metallic 
rhodium may be obtained by ignition. 

With sulphur, rhodium combines energetically at a high temperature ; a protosul- 
phide and a sesquisulphide have been obtained. 

An alloy of gold with between 30 and 40 per cent, of rhodium has been found in 
Mexico. 

293. Osmium (Os = 199) is characterised by its yielding a.very volatile acid oxide 
(osmic acid, Os0 4 ), the vapours of which have a very irritating odour (o^jj, odour). 
It occurs in the ores of platinum in flat scales, consisting of an alloy of osmium, 
iridium, ruthenium, and rhodium. This alloy is also found associated with native 

* Palladium, at a slightly elevated temperature, absorbs, mechanically, many times its 
volume of hydrogen. Hammered palladium foil condenses 640 times its volume of hydro- 
gen, below 212° F., though it has not the power of absorbing oxygen or nitrogen. Foil 
made from fused palladium onlv absorbs 68 times its volume of hydrogen. — (Graham, Proa 
Roy. Soc., June 1866). 



RUTHENIUM — IRIDIUM. 395 

gold, and being very heavy, it accumulates at the bottom of the crucible in which 
the gold is melted. The osmium alloy is extremely hard, and has been used to tip 
the points of gold pens. When a grain of it happens to be present in the gold 
which is being coined, it often seriously injures the die. When the platinum ore 
is treated with aqua regia, this alloy is left undissolved, together with grains of 
chrome- iron ore and titanic iron. To extract the osmium from this residue, it is 
heated in a porcelain tube through which a current of dry air is passed, when the 
osmium is converted into osmic acid, the vapour of which is carried forward by the 
current of air and condensed in bottles provided to receive it. The osmic acid forms 
colourless prismatic crystals which fuse and volatilise below the boiling-point of 
water, yielding a most irritating vapour resembling chlorine. It is very soluble in 
water, giving a solution which exhales the odour of the acid and stains the skin 
black ; tincture of galls gives a blue precipitate w T ith the solution. Its acid properties 
are feeble, for it neither reddens litmus nor decomposes the carbonates, and its salts 
are decomposed by boiling their solutions. By adding hydrosulphuric acid to a 
solution of osmic acid, the tetrasulphide of osmium (OsS 4 ) is obtained as a black 
precipitate, and if this be carefully dried and heated in a crucible made of gas-carbon , 
metallic osmium is obtained as a brittle mass (sp. gr. 21 "4), which is not fused even 
by the oxyhydrogen blowpipe, and is not soluble in acids. When obtained by other 
processes in a finely divided state, osmium oxidises even at the ordinary temperature, 
and emits the odour of osmic acid. In this state, also, it may be dissolved by nitric 
acid, which converts it into osmic acid. 

By dissolving osmic acid in potash and adding alcohol, the latter is oxidised at 
the expense of the osmic acid, and rose-coloured octahedral crystals of osmite of potash 
(K 2 O.Os0 3 , 2Aq.) are obtained ; the osmious acid has not been isolated. A protoxide 
and a binoxide of osmium have been obtained. 

Osmium appears to form four chlorides — bichloride (OsCl 2 ), terchloride (OsCl 3 ), 
tetrachloride (OsCl 4 ), and hexachloride (OsCl 6 ). The bichloride and tetrachloride are 
formed by the direct combination of chlorine with osmium ; the former sublimes in 
green needles, which yield a blue solution in water, soon absorbing oxygen from the 
air and becoming converted into tetrachloride. By heating a mixture of pulverulent 
osmium with chloride of potassium in a current of chlorine, a double chloride ot 
osmium and potassium (2KC1, OsCl 4 ) is obtained, which is sparingly soluble, and 
crystallises in octahedra like the corresponding salt of platinum. When decomposed 
with nitrate of silver it gives a dark green precipitate (2AgCl, OsCl 4 ). 

294. Ruthenium (Ru = 104'2).* — In the process for extracting osmium from the 
residue left on treating the platinum ore with aqua regia, by heating in a current of 
air, square prismatic crystals of binoxide of ruthenium (Ru0 2 ) are deposited, nearer 
to the heated portion of the tube than the osmic acid, for the binoxide is not itself 
volatile, being only carried forward mechanically in company with the osmic acid. 
When binoxide of ruthenium is heated in hydrogen, metallic ruthenium is obtained 
as a hard, brittle, almost infusible metal, which is scarcely affected even by aqua 
regia. The protoxide of ruthenium (RuO) is a dark grey powder insoluble in acids. 
The sesquioxide (Ru 2 3 ) and the binoxide (Ru0 2 ) have feebly basic properties. The 
sesquioxide is not decomposed by heat. The anhydrous binoxide is a greenish blue 
powder. Ruthenic acid (Ru0 3 ) is known only in combination with bases. 

295. Iridium (Ir=197'l), named from Iris, the rainbow, in allusion to the varied 
colours of its compounds, has been mentioned above as occurring in the insoluble 
alloy from the platinum ores. It is also sometimes found separately, and occasion- 
ally alloyed with platinum, the allojfr crystallising in octahedra, which are even 
heavier than platinum (sp. gr. 22*3). If the insoluble osmiridium alloy left by aqua 
regia be mixed with common salt and heated in a current of chlorine, a mixture of 
the sodio-chlorides of the metals is obtained, and may be extracted by boiling water. 
If the solution be evaporated and distilled with nitric acid, the osmium is distilled 
off as osmic acid, and by adding chloride of ammonium to the residual solution, the 
iridium is precipitated as a dark red-brown ammonio-chloride ( (2NH 3 , HC1), IrCl 4 ) 
which leaves metallic iridium when heated. Like platinum, it then forms a grey 
spongy mass, but is oxidised when heated in air, and may be fused with the oxy- 
hydrogen blowpipe to a hard brittle mass (sp. gr. 21 - 2), which does not oxidise in 
air. Like rhodium it is not attacked by aqua regia, unless alloyed with platinum. 
The product of the oxidation of finely divided iridium in air is the sesquioxide (lr 2 3 ), 
which is a black powder used for imparting an intense black to porcelain ; it is 

* A new mineral found in Borneo, and named laurile, contains sulphides of ruthenium 
and osmium. It forms small lustrous granules. 



396 



OCCURRENCE OF GOLD IN NATURE. 



insoluble in acids. The protoxide (IrO) is also more easily acted upon by alkalies 
than by acids ; its solution in potash becomes blue when exposed to air, from the 
formation of the binoxide (Ir0 2 ). The teroxide (Ir0 3 ) is green. The bichloride (IrCl 2 ) 
and tetrachloride (IrCl 4 ) of iridium resemble the corresponding chlorides of platinum 
in forming double salts with the alkaline chlorides. There is also a trichloride 
(IrCl 3 ), the solution of which has a green colour, and gives a yellow precipitate 
with mercurous nitrate, and a blue precipitate, soon becoming white, with nitrate 
of silver. Iridium resembles palladium in its disposition to combine with carbon 
when heated in the flame of a spirit-lamp. 

296. The following table exhibits a general view of the analytical process by which 
the remarkable metals associated in the ores of platinum may be separated from 
each other, omitting the minor details which are requisite to ensure the purity of 
each metal. 

Analysis of the Ore of Platinum. 
Boil with aqua regia. 



Dissolved. 
Platinum, Palladium, Rhodium. 

Add chloride of ammonium. 


Undissolved. 

Iridium, Osmium, Ruthenium. 

Chrome iron, Titanic iron, &c. 

Heat in current of dry air. 


Precipitated ; 

Platinum 

as 

2NH 4 CL, PtCl 4 . 


Solution : 

Neutralise with carbonate of soda ; 

add cyanide of mercury. 


Volatilised 
Osmium 
as Os0 4 . 


Carried 
forward by 
the current; 
Ruthenium 

as Ru0 2 . 


Residue ; 

Mix with chloride of 

sodium, and heat in 

current of chlorine. 

Treat with boiling water. 


Precipitated ; 
Palladium 
as PdCy 2 . 


Solution ; 

Evaporate with 

hydrochloric acid. 

Treat with alcohol. 

Insoluble. 

Rhodium 

as 3NaCl.RoCl 3 . 


Dissolved. 

Iridium 

as2NaClirCl 4 . 


Residue. 

Titanic iron, 

Chrome iron, 

&c. 



The group of platinoid metals exhibits some very remarkable features, and it is to be 
regretted that this group is comparatively imperfectly known in consequence of the diffi- 
culty and expense attendant upon the purification of the metals. Its members may 
be arranged in two divisions, the metals in each agreeing closely in their atomic 
weights and specific gravities. 





Atomic weight. 


Sp. gr. 




Atomic weight. 


Sp. gr. 


Platinum, . 


197-1 


21-5 


Palladium, . 


106-5 


11-4 


Osmium, 


199-0 


21-4 


Khodium, . 


104-3 


12-1 


Iridium, 


197-1 


21-2 


Kuthenium, 


104-2 


11-4 



Through osmium, this group of elements is connected with the group containing 
antimony, arsenic, and phosphorus, which osmium resembles in the facility with 
which it is oxidised, and in the volatility of the oxide formed. Palladium connects 
it with mercury and silver, by its solubility in nitric acid, and its special attraction 
for cyanogen and iodine. 



GOLD. 

Au = 196'6 parts by weight. 

297. Gold is one of those few metals which are always found in the 
metallic state, and is remarkable for the extent to which it is distributed, 
though in small quantities, over the surface of the earth. The principal 
supplies of this metal are derived from Australia, California, Mexico, 
Brazil, Peru, and the Uralian Mountains. Small quantities have been 
occasionally met with in oar own islands, particularly at Wicklow, at 
Cader Idris in Wales, Leadhills in Scotland, and in Cornwall. 

The mode of the occurrence of gold in the mineral kingdom resembles 
that of the ore of tin, for it is either found disseminated in the primitive 



SMELTING OF GOLD ORES. 397 

rocks, or in alluvial deposits of sand, which, appear to have been formed 
by the disintegration of those rocks under the continued action of torrents. 
In the former case, the gold is often found crystallised in cubes and octa- 
hedra, or in forms derived from these, and sometimes aggregated together 
in dendritic or branch-like forms. In the alluvial deposits, the gold is 
usually found in small scales (gold dust), but sometimes in masses of con- 
siderable size (nuggets), the rounded appearance of which indicates that 
they have been subjected to attrition. 

The extraction of the particles of gold from the alluvial sands is effected 
by taking advantage of the high specific gravity of the metal (19*3), which 
causes it to remain behind, whilst the sand, which is very much lighter 
(sp. gr. 2*6), is carried away by water. This washing is commonly 
performed by hand, in wooden or metal bowls, in which the sand is 
shaken up with water, and the lighter portions dexterously poured off, so 
as to leave the grains of gold at the bottom of the vessel. On a somewhat 
larger scale, the auriferous sand is washed in a cradle or inclined wooden 
trough, furnished with rockers, and with an opening at the lower end for 
the escape of the water. The sand is thrown on to a grating at the head 
of the cradle, which retains the large pebbles, whilst the sand and gold 
pass through, the former being washed away by a stream of water which 
is kept flowing through the trough. 

When the gold is disseminated through masses of quartz or other rock, 
much labour is expended in crushing the latter before the gold can be 
separated. This is effected either by passing the coarse fragments between 
heavy rollers of hard cast-iron, or by stamping them, with wooden beams 
shod with iron, in troughs through which water is kept continually 
flowing. 

In some cases it is found advantageous to smelt the ore by fusing it 
with some substance capable of uniting with the gold, and of being after- 
wards readily separated from it. Lead is peculiarly adapted for this pur- 
pose ; the crushed ore, being mixed with a suitable proportion, either of 
metallic lead, or of litharge (oxide of lead) and charcoal, or even of galena 
(sulphide of lead), together with some lime and oxide of iron or clay, to 
flux the silica, is fused on the hearth of a reverberatory furnace, when the 
fused lead dissolves the particles of gold, and collects beneath the lighter 
slag. The lead is afterwards separated from the gold by cupellation (see 
p. 351.) 

In smelting the ores of gold in Hungary, the metal is concentrated by 
means of sulphide of iron. The ore consists of quartz and iron pyrites 
(bisulphide of iron) containing a little gold. On fusing the crushed ore 
with lime, to flux the quartz, the pyrites loses half its sulphur, and becomes 
sulphide of iron (FeS), which fuses and sinks below the slag, carrying with 
it the whole of the gold. If this product be roasted so as to convert the 
iron into oxide, and be then again fused with a fresh portion of the ore, 
the oxide of iron will flux the quartz, whilst the fresh portion of sulphide 
of iron will carry down the whole of the gold contained in both quantities 
of ore. This operation having been repeated until the sulphide of iron 
is rich in gold, it is fused with a certain quantity of lead, which extracts 
the gold and falls to the bottom. The lead is then cupelled in order to 
obtain the gold. 

When the ores of lead, silver, or copper contain gold, it is always found 
to have accompanied the silver extracted from them, and is separated from 
it by a process to be presently noticed. 



398 REFINING GOLD. 

Gold is sometimes separated from the impurities remaining with it after 
extraction by washing, by the process of amalgamation, which consists in 
shaking the mixture with mercury in order to dissolve the gold-dust, and 
straining the liquid amalgam through a chamois leather, which allows the 
excess of mercury to pass through, but retains the solid portion containing 
the gold, from which the mercury is then separated by distillation.* 

In the Tyrol, this process is adopted for separating the gold from an 
auriferous iron pyrites, by grinding it in a mill of peculiar construction, 
with water and a little mercury, the latter being allowed to act upon suc- 
cessive portions of ore until it becomes sufficiently rich to be strained and 
distilled. 

Gold, as found in nature, is generally alloyed with variable proportions 
of silver and copper, the separation of which is the object of the gold 
refiner. It may be effected by means of nitric acid, which will dissolve 
the silver and copper, provided that they do not bear too small a propor- 
tion to the gold. Sulphuric acid, however, being very much cheaper, is 
generally employed. The alloy is fused and poured into water, so as to 
granulate it and expose a larger surface to the action of the acid; it is then 
boiled with concentrated sulphuric acid (oil of vitriol), which converts the 
silver and the copper into sulphates, with evolution of sulphurous acid gas, 
whilst the gold is left untouched. In order to recover the silver from the 
solution of the sulphates in water, scraps of copper are introduced into 
it, when that metal decomposes the sulphate of silver, producing sulphate 
of copper, and causing the deposition of the silver in the metallic state. 
Finally, the sulphate of copper may be obtained from the solution by 
evaporation and crystallisation. This process is so effectual when the 
proportion of gold in an alloy is very small, that even g^th part of this 
metal may be profitably extracted from 100 parts of an alloy, and much 
gold has been obtained in this way from old silver plate, coins, &c, which 
were manufactured before so perfect a process for the separation of these 
metals was known. On boiling old silver coins or ornaments with nitric 
acid, they are generally found to yield a minute proportion of gold in the 
form of a purple powder. But this plan of separation is not so successful 
when the alloy contains a very large quantity of gold, for the latter metal 
seems to protect the copper and silver from the solvent action of the acid. 
Thus, if the alloy contains more than -^th of its weight of gold, it is 
customary to fuse it with a quantity of silver, so as to reduce the propor- 
tion of gold below that point, before boiling it with the acid. Again, if 
the alloy contains a large quantity of copper, it is found expedient to 
remove a great deal of this metal in the form of oxide by heating the alloy 
in a current of air. 

Gold which is brittle and unfit for coining, in consequence of the pre- 
sence of small quantities of foreign metals, is sometimes refined by melting 
it with oxide of copper or with a mixture of nitre and borax, when *the 
foreign metals, with the exception of silver, are oxidised and dissolved in 
the slag. Another process consists in throwing some corrosive sublimate 
(chloride of mercury) into the melting pot, and stirring it up with the 
metal, when its vapour converts the metallic impurities into chlorides, 
which are volatilised. An excellent method, devised by F. B. Miller of 
Sydney, consists in fusing the gold with a little borax, and passing chlo- 

* A small quantity of sodium dissolved in the mercury has been found very materially 
to facilitate the amalgamation of gold and silver ores, apparently because the amalgam 
of sodium is more highly electropositive than mercury, in relation to the gold. 



PKOPERTIES OF GOLD. 399 

rine gas into it through a clay tube. Antimony, arsenic, &c, are carried 
off as chlorides, whilst the silver, also converted into chloride, rises to the 
surface of the gold in a fused state, afterwards solidifying into a cake, 
which is reduced to the metallic state by placing it between plates of 
wrought-iron and immersing it in diluted sulphuric acid. 

Pure gold, like pure silver, is too soft to resist the wear to which it is 
subjected in its ordinary uses, and it is therefore alloyed for coinage in 
this country with ^th of its weight of copper, so that gold coin contains 
1 part of copper and 11 parts of gold. The gold used for articles of 
jewellery is alloyed with variable proportions of copper and silver. The 
alloy of copper and gold is much redder than pure gold. 

The degree of purity of gold is generally expressed by quoting it as of 
so many carats fine. Thus, pure gold is said to be 24 carats fine; English 
standard gold is 22 carats fine, that is, contains 22 carats of gold out of 
the 24. Gold of 18 carats fine would contain! 8 parts of gold out of the 
24, or fths of its weight of gold. 

Pure gold is easily prepared from standard or jeweller's gold, by dissolving it in 
hydrochloric acid mixed with one-fourth of its volume of nitric acid, evaporating 
the solution to a small bulk to expel excess of acid, diluting with a considerable 
quantity of water, filtering from the separated chloride of silver, and adding a solution 
of sulphate of iron, when the gold is precipitated as a dark purple powder, which 
may be collected on a filter, well washed, dried, and fused in a small French clay 
crucible with a little borax, the crucible having been previously dipped in a hot 
saturated solution of borax, and dried, to prevent adhesion of the globules of gold. 
The action of the sulphate of iron upon the terchloride of gold is explained by the 
equation — 

2AuCl 3 + 6(FeO.S0 3 ) = Au 2 + Fe 2 Cl 6 + 2(Fe 2 O s .3S0 3 ). 

By employing oxalic acid instead of sulphate of iron, and heating the solution, 
the gold is precipitated in a spongy state, and becomes a coherent lustrous mass 
under pressure. The metal is employed in this form by dentists. 

When standard gold is being dissolved in aqua regia, it sometimes becomes coated 
with a film of chloride of silver which stops the action of the acid ; the liquid must 
then be poured off, the metal washed, and treated with ammonia, which dissolves 
the chloride of silver ; the ammonia must be washed away before the metal is replaced 
in the acid. In the case of jeweller's gold, it is advisable to extract as much silver 
and copper as possible by boiling it with nitric acid, before attempting to dissolve 
the gold. Gold lace should be incinerated to get rid of the cotton before being 
treated with acid. 

The genuineness of gold trinkets, &c, is generally tested by touching them with 
nitric acid, which attacks them if they contain a very considerable proportion of 
copper, producing a green stain, but this test is evidently useless if the surface be 
gilt. The weight is, of course, a good criterion in practised hands, but even these 
have been deceived by bars of platinum covered with gold. The specific gravity 
may be taken in doubtful cases ; that of sovereign gold is 17 '157. 

In assaying gold, the metal is wrapped in a piece of thin paper together with about 
three times its weight of pure silver, and added to twelve times its weight of pure 
lead fused in a bone-ash cupel (see page 352) placed in a muffle (or exposed to a 
strong oxidising blowpipe flame), when the lead and copper are oxidised, and the 
fused oxide of lead dissolves that of copper, both being absorbed by the cupel. 
When the metallic button no longer diminishes in size, it is allowed to cool, hammered 
into a flat disk which is annealed by being heated to redness, and rolled out to a 
thin plate, so that it may be rolled up by the thumb and finger into a comette which 
is boiled with nitric acid (sp. gr. 1 *18) to extract the silver ; the remaining gold is 
washed with distilled water, and boiled, with nitric acid of sp. gr. 1 - 28, to extract the 
last traces of silver, after which it is again washed, heated to redness in a small 
crucible, and weighed. 

The stronger nitric acid could not be used at first, since it would be likely to break 
the cornet into fragments which could not be so readily washed without loss. The 
addition of the three parts of silver (quartation) is made in order to divide the alloy, 
and permit the easy extraction of the silver by nitric acid, which cannot be effected 
when the gold predominates. 



400 PROPERTIES OF GOLD. 

298. The physical characters of gold render it very conspicuous among 
the metals ; it is the heaviest of the metals in common use, with the 
exception of platinum, its specific gravity being 19*3. In malleability 
and ductility it surpasses all other metals ; the former property is turned 
to advantage for the manufacture of gold leaf, for which purpose a bar of 
gold is passed between rollers which extend it into the form of a riband ; 
this is cut up into squares, which are packed between layers of fine vellum, 
and beaten with a heavy hammer ; these thinner squares are then again 
cut up and beaten between layers of gold-beater's skin until they are suffi- 
ciently thin. An ounce of gold may thus be spread over 100 square feet ; 
282,000 of such leaves placed upon each other form a pile of only one 
inch high. These leaves will allow light to pass through them, and 
always appear green or blue when held up to the light, though they exhibit 
the ordinary colour of gold by reflected light ; extremely thin leaves of 
gold, obtained by partially dissolving ordinary gold leaf by floating it on 
solution of cyanide of potassium, transmit a violet or a red light, accord- 
ing to their thickness, though they still appear yellow by reflected light, 
and if taken up on a glass plate and heated to about 600° F. they lose 
their golden reflection and become ruby red, changing to green if pressed 
with a hard substance. If very finely divided gold be suspended in 
water, it imparts a violet or red colour to it. Such coloured fluids 
containing very minute particles of gold in a state of suspension, may be 
obtained by the action of phosphorus dissolved in ether upon a very weak 
solution of gold in aqua regia ; on standing for a long time, the particles 
of finely divided gold are deposited, having the same tint as that which 
they previously exhibited when suspended in the liquid ; the blue parti- 
cles being less minute are soonest deposited, but the red particles require 
many months to settle down. These divers colours of finely divided gold 
are taken advantage of in painting upon porcelain, and the well-known 
magnificent ruby red glass owes its colour to the same cause. T^o"* n °^ 
a grain of gold is capable of imparting a deep rose colour to a cubic inch 
of fluid. 

The extreme ductility of gold is exemplified in the manufacture of gold 
thread for embroidery, in which a cylinder of silver having been covered 
with gold leaf, it is drawn through a wire-drawing plate and reduced to 
the thinness of a hair ; in this way six ounces of gold are drawn into a 
cylinder two hundred miles in length. Although fusing at about the 
same temperature as copper, gold is seldom cast, on account of its great 
contraction during solidification. 

Gold is not even affected to the same extent as silver by exposure to the 
atmosphere, for sulphuretted hydrogen has no action upon it, and hence 
no metal is so well adapted for coating surfaces which are required to 
preserve their lustre. 

The gold is sometimes applied to the surfaces of metals in the form of 
an amalgam, the mercury being afterwards driven off by heat. Metals 
may also be gilt by means of a boiling solution prepared by dissolving 
gold in aqua regia, and adding an excess of bicarbonate of potash or of 
soda. But the most elegant process of gilding is that of electro-gilding, 
in which the object to be gilt is connected with the negative (zinc) end 
of the galvanic battery, and immersed in a solution of cyanide of gold in 
cyanide of potassium, in which is also placed a gold plate connected with 
the positive (copper) end of the battery, and intended, by gradually dis- 
solving, to replace the gold abstracted from the solution at the negative pole. 



OXIDES OF GOLD. 401 

A gold crucible is very useful in the laboratory for effecting the fusion 
of substances with caustic alkalies, which would corrode a platinum 
crucible. 

299. Oxides of gold. — Two compounds of gold with oxygen have been 
obtained, Au 2 and Au 2 3 , but neither of them is of any great practical 
importance. 

Sesquioxide of gold or auric acid (Au 2 3 ) is prepared from the solution 
of gold in aqua regia, by boiling it with excess of potash, decomposing 
the aurate of potash with sulphuric acid, and purifying the auric acid 
by dissolving it in nitric acid and precipitating by water. It forms a 
yellow precipitate, which is easily decomposed by exposure to light or to 
a temperature of 500° F. By dissolving it in potash and evaporating in 
vacuo, the aurate of potash is obtained in yellow needles (K 2 0. Au 2 3 , 6Aq.). 
Suboxide of gold (Au 2 0) forms a dark precipitate when protochloride of 
gold is decomposed by potash. 

The chlorides of gold correspond in composition to the oxides. The 
terchloride of gold (AuCl 3 ) is obtained by dissolving gold in hydrochloric 
acid with one-fourth of its volume of nitric acid, and evaporating on a 
water-bath to a small bulk ; on cooling, yellow prismatic crystals of a 
compound of the terchloride with hydrochloric acid (AuCl 3 .HC1.6Aq.) 
are deposited, from which the hydrochloric acid may be expelled by a 
gentle heat (not exceeding 250° F.), when the terchloride forms a red 
brown deliquescent mass, dissolving very readily in water, giving a bright 
yellow solution which stains the skin and other organic matter purple 
when exposed to light, depositing finely divided gold. Almost every 
substance capable of combining with oxygen reduces the gold to the 
metallic state. The inside of a perfectly clean flask or tube may be 
covered with a film of metallic gold by a dilute solution of the terchloride 
mixed with citric acid and ammonia, and gently heated. The facility 
with which it deposits metallic gold, and the resistance of the deposited 
metal to atmospheric action, has rendered terchloride of gold very useful 
in photography. Alcohol and ether readily dissolve the terchloride, the 
latter being able to extract it from its aqueous solution. Eed crystals 
of terchloride of gold are sublimed when thin^gold foil is gently heated 
in a current of chlorine. Terchloride of gold (like perchloride of platinum) 
forms crystallisable compounds with the alkaline chlorides and with the 
hydrochlorates of organic bases, and affords great help to the chemist in 
defining these last. Aurochloride of sodium forms reddish yellow prismatic 
crystals (]STaCl.AuCl 3 ,4Aq.) which are sometimes sold for photographic 
purposes. 

Protochloride of gold (AuCl) is obtained by gently heating the terchlo- 
ride, when it fuses and is decomposed at 350° F., leaving the protochloride, 
which is reduced to metallic gold at about 400° F. The protochloride is 
sparingly soluble in water and of a pale-yellow colour. Boiling water 
decomposes it into metallic gold and terchloride. 

Fulminating gold is obtained as a buff precipitate when ammonia is 
added to solution of terchloride of gold ; its composition is not well estab- 
lished, but appears to be Au 2 3 .4MI 3 .H 2 0. It explodes violently when 
gently heated. 

The Sel d'or of the photographer is a hyposulphite of gold and soda 
(Au 2 S 2 3 , 3(Na 2 S 2 3 ), 4Aq.), which, is obtained in fine white needles 
by pouring a solution of one part of terchloride of gold into a solution of 

2 c 



402 SULPHIDES OF GOLD. 

three parts of hyposulphite of soda, and adding alcohol, in which the 
double salt is insoluble. Its formation may be explained by the equation — 

8(Na 2 S 2 3 ) + 2AuCl 3 = Au 2 S 2 3 , 3(Na 2 S 2 3 ) + 6NaCl + 2(Na 2 S 4 6 ) . 

It is doubtful whether the above formula represents the true constitution 
of this salt, for it is not decomposed by acids in the same manner as ordi- 
nary hyposulphites. Nitric acid causes the whole of the gold to separate 
in the metallic state. 

Purple of Oassius, which is employed for imparting a rich red colour to 
glass and porcelain, is a compound of gold, tin, and oxygen, which are be- 
lieved to be grouped according to the formula Au 2 O.Sn0 2 , SnO.Sn0 2 .4Aq. 
It may be prepared by adding protochloride of tin to a mixture of bi- 
chloride of tin and terchloride of gold ; 7 parts of gold are dissolved in 
aqua regia and mixed with 2 parts of tin also dissolved in aqua regia ; 
this solution is largely diluted with water, and a weak solution of 1 part 
of tin in hydrochloric acid is added, drop by drop, till a fine purple colour 
is produced. The purple of Cassius remains suspended in water in a very 
fine state of division, but subsides gradually, especially if some saline 
solution be added, as a purple powder. The fresh precipitate dissolves in 
ammonia, but the purple solution is decomposed by exposure to light, 
becoming blue, and finally colourless, metallic gold being precipitated, 
and binoxide of tin left in solution. 

The sulphides of gold are not thoroughly known. When hydrosul- 
phuric acid acts on solution of terchloride of gold, a black precipitate of 
Au 2 S, Au 2 S 3 is obtained, which dissolves in alkaline sulphides. The salt 
Na 2 S, Au 2 S, 8Aq. has been obtained, in colourless prisms soluble in 
alcohol. The precipitated sulphide of gold is not dissolved by the acids, 
with the exception of aqua regia. Nitric acid oxidises the sulphur, 
leaving metallic gold. When hydrosulphuric acid is added to a boiling 
solution of terchloride of gold, the metal itself is precipitated — 

8AuCl 3 + 3H 2 S + 12H 2 = Au 8 + 24HC1 + 3(H 2 O.S0 3 ). 

A yellowish grey brittle arsenide of gold (AuAs 2 ) has been found in 
quartz in Australia. 



ON SOME OF THE 

USEFUL APPLICATIONS OF CHEMICAL PRINCIPLES 
NOT HITHERTO MENTIONED. 



CHEMICAL PKLNCIPLES OF THE MANUFACTUBE 
OF GLASS. 

300. Glass is defined chemically to be a mixture of two or more sili- 
cates, one of which is a silicate of an alkali, the other being a silicate of 
lime, baryta, oxide of iron, oxide of lead, or oxide of zinc. 

If silicic acid be fused with an equal weight of carbonate of potash or 
soda, a transparent glassy mass is obtained, but this is slowly dissolved by 
water, and would therefore be incapable of resisting the action of the 
weather ; if a small proportion of lime or baryta, or of the oxides of iron, 
lead, or zinc, be added, the glass becomes far less easily affected by atmo- 
spheric influences. 

The most valuable property of glass, after its transparency and per- 
manence, is that of assuming a viscid or plastic consistency when fused; 
which allows it to be so easily fashioned into the various shapes required 
for use or ornament. 

The composition of glass is varied according to the particular purpose 
for which it is intended, the materials selected being fused in large clay 
crucibles placed in reverberatory furnaces, and -heated by a coal-fire or in 
a gas-furnace. 

Ordinary window glass is essentially composed of silicate of soda and 
silicate of lime, containing one molecule (13'3 per cent.) of soda, one 
molecule (12'9 per cent.) of lime,. and five molecules (69*1 per cent.) of 
silicic acid ; it also usually contains a little alumina. This variety of glass 
is manufactured by fusing 100 parts of sand with about 35 parts of chalk 
and 35 parts of soda-ash : a considerable quantity of broken window glass 
is always fused up at the same time. Of course, the carbonic acid of the 
chalk and of the carbonate of soda is expelled in the gaseous state, and in 
order that this may not cause the contents of the crucible to froth over 
during the fusion, the materials are first fritted together, as it is termed, 
at a temperature insufficient to liquefy them, when the carbonic acid 
is evolved gradually, and the fusion afterwards takes place without 
effervescence. 

Occasionally sulphate of soda is employed instead of the carbonate, 
when it is usual to add a small proportion of charcoal, in order to reduce 
the sulphuric to the state of sulphurous acid, which is far more easily 
expelled. Before the glass is worked into sheets, it is allowed to remain 



404 FLINT GLASS — COLOURED GLASS. 

at rest for some time in the fused state, so that the air-bubbles may 
escape, and the glass-gall or scum (consisting chiefly of sulphate of soda 
and chloride of sodium), which rises to the surface, is removed. 

Plate glass is also chiefly a silicate of soda and lime, but it contains, 
in addition, a considerable quantity of silicate of potash (74 per cent, 
of silicic acid, 12 of soda, 5*5 of potash, and 5*5 of lime). The purest 
white sand is selected, and great care is taken to exclude impurities. 

Grown glass, used for optical purposes, contains no soda, since that 
alkali has the property of imparting a greenish tint to glass, which is 
not the case with potash. This variety of glass, therefore, is prepared 
by fusing sand with carbonate of potash and chalk in such proportions 
that the glass may contain one molecule (22 per cent.) of potash, one 
molecule (12*5 per cent.) of lime, and four molecules (62 per cent.) 
of silicic acid. 

The glass of which wine bottles are made is of a much cheaper and com- 
moner description, consisting chiefly of silicate of lime, but containing, in 
addition, small quantities of the silicates of the alkalies, of alumina, and 
of oxide of iron, to the last of which it owes its dark colour. It is 
made of the coarsest materials, such as common red sand (containing 
iron and alumina), soap-makers' waste (containing lime and small quan- 
tities of alkali), refuse lime from the gas-works, clay, and a very small 
proportion of rock-salt. 

Flint glass, which is used for table glass and for ornamental pur- 
poses, is a double silicate of potash and oxide of lead, containing one 
molecule (13*67 per cent.) of potash, one molecule (33*28 per cent.) 
of oxide of lead, and six molecules (51*93 per cent.) of silicic acid. 
It is prepared by fusing 300 parts of the purest white sand with 200 
parts of minium (red oxide of lead), 100 parts of refined pearl-ash, and 
30 parts of nitre. The fusion is effected in crucibles covered in at the 
top to prevent the access of the flame, which would reduce a portion 
of the lead to the metallic state. The nitre is added in order to oxidise 
any accidental impurities which might reduce the lead. 

The presence of the oxide of lead in glass very much increases its 
fusibility, and renders it much softer, so that it may be more easily cut- 
into ornamental forms ; it also greatly increases its lustre and beauty. 

Baryta has also the effect of increasing the fusibility of glass, and oxide 
of zinc, like oxide of lead, increases its brilliancy and refracting power, 
on which account it is employed in some kinds of glass for optical pur- 
poses. Glass of this description is also made by substituting boracic acid 
for a portion of the silicic acid. 

Some varieties of glass, if heated nearly to their melting point, and 
allowed to cool slowly, become converted into an opaque very hard mass 
resembling porcelain (Reaumur's porcelain). This change, which is known 
as devitrification, is due to the crystallisation of the silicates contained in 
the mass, and by again fusing it, the glass may be restored to its original 
transparent condition. 

In producing coloured glass, advantage is taken of its property of dis- 
solving many metallic oxides with production of peculiar colours. It has 
been mentioned above that bottle glass owes its green colour to the pre- 
sence of oxide of iron ; and since this oxide is generally found in small 
quantity in sand, and even in chalk, it occasionally happens that a glass 
which is required to be perfectly colourless turns out to have a slight green 
tinge. In order to remove this, a small quantity of some oxidising agent 



POTTERY AND PORCELAIN. 405 

is usually added, in order to convert the oxide of iron into the sesquioxide, 
which does not impart any colour when present in minute proportion. A 
little nitre is sometimes added for this purpose, or some arsenious acid, 
which yields its oxygen to the oxide of iron, and escapes in the form of 
vapour of arsenic ; red oxide of lead (Pb 3 4 ) may also be employed, and 
is reduced to oxide of lead (PbO), which remains in the glass. Bin- 
oxide of manganese is often added as an oxidising agent, being reduced 
to the state of oxide of manganese (MnO), which does not colour the 
glass ; but care is then taken not to add too much of the binoxide, for a 
very minute quantity of this substance imparts a beautiful amethyst purple 
colour to glass. 

Suboxide of copper is used to produce a red glass, and the finest ruby 
glass is obtained (as already mentioned at p. 400) by the addition of a 
little gold. The oxides of antimony impart a yellow colour to glass ; a 
peculiar brown-yellow shade is given by charcoal in a fine state of division, 
and sesquioxide of uranium produces a fine greenish-yellow glass. Green 
glass is coloured either by oxide of copper or sesquioxide of chromium, 
whilst oxide of cobalt gives a magnificent blue colour. For black glass, 
a mixture of the oxides of cobalt and manganese is employed. The white 
enamel glass is a flint glass, containing about 10 per cent, of binoxide of 
tin. Bone ash is also used to impart this appearance to glass. 

CHEMISTEY OF THE MANUFACTURE OF POTTEKY 
AND POECELAIK 

301. The manufacture of pottery obviously belongs to an earlier period 
of civilisation than that of glass, since the raw material, clay, would at 
once suggest, by its plastic properties, the possibility of working it into 
useful vessels, and the application of heat would naturally be had recourse 
to in order to dry and harden it. Indeed, at the first glance, it would 
appear that this manufacture, unlike that of glass, did not involve the 
application of chemical principles, but consisted simply in fashioning the 
clay by mere mechanical dexterity into the required form. It is found, 
however, at the outset, that the name of clay is applied to a large class of 
minerals, differing very considerably in composition, and possessing in 
common the two characteristic features of plasticity and a predominance 
of silicate of alumina. 

It has already been stated (p. 285) that kaolin is a hydrated silicate 
of alumina, and it is from this material that the best variety of porcelain 
is made. This clay is eminently plastic, and can therefore be readily 
moulded, but when baked, it shrinks very much, so that the vessels made 
from it lose their shape and often crack in the kiln. In order to prevent 
this, the clay is mixed with a certain proportion of sand, chalk, bone-ash, 
or heavy-spar ; but another difficulty is thus introduced, for these sub- 
stances diminish the tenacity of the clay, and would thus render the 
vessels brittle. A further addition must therefore be made, of some sub- 
stance which fuses at the temperature employed in baking the ware, and 
thus serves as a cement to bind the unfused particles of clay, &c, into 
a compact mass. Feldspar (silicate of alumina and potash) answers this 
purpose ; or carbonate of potash or of soda is sometimes added, to convert 
a portion of the silica into a fusible alkaline silicate. With a mixture of 
clay with sand and feldspar (or some substitutes), a vessel may be moulded 
which will preserve its shape and tenacity when baked, but it will be 



406 ENGLISH PORCELAIN — STONE- WARE. 

easily pervious to water, and thus quite unfit for ordinary use. It has, there- 
fore, to be water-proofed by the application of some easily fusible material, 
which shall either form a glaze over the surface, or shall become incor- 
porated with the body of the ware, and the vessel is then fit for all its 
uses. Handles and ornaments in relief are moulded separately, and fixed 
on the ware before baking, and coloured designs are transferred from 
paper to the porous ware before glazing. 

The manufacture of Sevres porcelain is one of the most perfect examples 
of this art. The purest materials are selected in the following propor- 
tions : — Kaolin (porcelain clay), 62 parts ; chalk, 4 parts ; sand, 17 parts ; 
feldspar, 17 parts. These materials are ground up with water before 
being mixed, and the coarser particles allowed to subside ; the creamy 
fluids containing the finer particles in suspension are then mixed in 
the proper proportions, and allowed to settle ; the paste deposited at the 
bottom is drained, thoroughly kneaded, and stored away for some months 
in a damp place, by which its texture is considerably improved, and any 
organic matter which it contains becomes oxidised and removed; the 
oxidation being effected partly by the sulphates present, which become 
reduced to sulphides. It is then moulded into the required forms, and 
dried by simple exposure to the air. The vessels are packed in cylindrical 
cases of very refractory clay, which are arranged in a furnace or kiln of 
peculiar construction, and very gradually but strongly heated by the 
flame of a wood fire. When sufficiently baked, the biscuit porcelain has 
to be glazed, and great care is taken that the glaze may possess the same 
expansibility by heat as the ware itself, for otherwise it would crack in all 
directions as the glazed ware cooled. The glaze employed at Sevres is a 
mixture of feldspar and quartz very finely ground, and suspended in 
water, to which a little vinegar is added to prevent the glaze from subsid- 
ing too rapidly. When the porous ware is dipped into this mixture, it 
absorbs the water, and retains a thin coating of the mixture of quartz and 
feldspar upon its surface. It is now baked a second time, when the glaze 
fuses, partly penetrating the ware, partly remaining as a varnish upon the 
surface. 

When the ware is required to have some uniform colour, a mineral 
pigment capable of resisting very high temperatures is mixed with the 
glaze ; but coloured designs are painted upon the ware after glazing, the 
ware being then baked a third time, in order to fix the colours. These 
colours are glasses coloured with metallic oxides, and ground up with oil 
of turpentine, so that they may be painted in the ordinary way upon the 
surface of the ware ; when the latter is again heated in the kiln, the 
coloured glass fuses, and thus contracts a firm adhesion with the ware. 

Gold is applied either in the form of precipitated metallic gold, or of 
fulminating gold, being ground up in either case with oil of turpentine, 
burnt in, and burnished. 

English porcelain is made from Cornish clay mixed with ground flints, 
burnt bones, and sometimes a little carbonate of soda, borax, and binoxide 
of tin, the last improving the colour of the ware. It is glazed with a 
mixture of Cornish stone (consisting of quartz and feldspar), flint, chalk, 
borax, and sometimes white lead to increase its fusibility. 

Stone-ware is made from less pure materials, and is covered with a glaze 
of silicate of soda, in a very simple manner, by a process known as salt- 
glazing. The ware is coated with a thin film of sand by dipping it in a 
mixture of fine sand and water, and is then intensely heated in a kiln into 



BUILDING MATERIALS. 407 

which a quantity of damp salt is presently thrown. The joint action of 
the aqueous vapour and the salt converts the sand into silicate of soda, 
which fuses into a glass upon the surface of the ware — 

2NaCl + H 2 + Si0 2 = Na 2 O.Si0 2 + 2HC1. 

Pipkins, and similar earthenware vessels, are made of common clay 
mixed with a certain proportion of marl and of sand. They are glazed 
with a mixture of 4 or 5 parts of clay, with 6 or 7 parts of litharge. The 
colour of this ware is due to the presence of peroxide of iron. 

Bricks and tiles are also made from common clay mixed, if necessary, 
with sand. These are very often grey, or blue, or yellow, before baking, 
and become red under the action of heat, since the iron, which is origin- 
ally present as carbonate (FeO.C0 2 ), becomes converted into the red 
peroxide (Fe 2 3 ) by the atmospheric oxygen. 

The impure varieties of clay fuse much more easily than pure clay, 
so that, for the manufacture of the refractory bricks for lining furnaces, 
of glass-pots, crucibles for making cast steel, &c, a pure clay is employed, 
to which a certain quantity of broken pots of the same material is added, 
to prevent the articles from shrinking whilst being dried. 

Dinas fire-bricks are made from a peculiar siliceous material found in 
the Vale of Neath, and containing alumina with about 98 per cent, of 
silica. The ground rock is mixed with 1 per cent, of lime and a little 
water before moulding. These bricks are expanded by heat, whilst 
ordinary fire-bricks contract. 

Blue bricks are glazed by sprinkling with iron scurf, & mixture of par- 
ticles of stone and iron produced by the wear of the siliceous grindstones 
employed in grinding gun-barrels, &c. "When the bricks are fired, a glaze 
of silicate of iron is formed upon them. 

CHEMISTEY OF BUILDING MATEEIALS. 

302. Chemical principles would lead to the selection of pure silica 
(quartz, rock-crystal) as the most durable of building materials, since it is 
not acted on by any of the substances likely to be present in the atmo- 
sphere ; but even if it could be obtained in sufficiently large masses for 
the purpose, its great hardness presents an obstacle to its being hewn into 
the required forms. Of the building stones actually employed, granite, 
basalt, and porjjhyry are the most lasting, on account of their capability 
of resisting for a great length of time the action of water and of atmo- 
spheric carbonic acid ; but their hardness makes them so difficult to work, 
as to prevent their employment except for the construction of pavements, 
bridges, &c, where the work is massive and straightforward, and much 
resistance to wear and tear is required. The millstone grit is also a very 
durable stone, consisting chiefly of silica, and employed for the founda- 
tions of houses. Freestone is a term applied to any stone which is soft 
enough to be wrought with hammer and chisel, or cut with a saw ; it 
includes the different varieties of sandstone and limestone. The sand- 
stones consist of grains of sand cemented together by clay or limestone. 
The Yorkshire flags employed for paving are siliceous stones of this 
description. The Craigleith sandstone, which is one of the freestones 
used in London, contains about 98 per cent, of silica, together with some 
carbonate of lime. 

The building stones in most general use are the different varieties of 



408 MORTAR — CEMENT. 

carbonate of lime. The durability of these is in proportion to their com- 
pact structure ; thus marble, being the most compact, has been found to 
resist for many centuries the action of the atmosphere, whilst the more 
porous limestones are corroded at the surface in a very short time. Port- 
land stone, of which St Paul's and Somerset House are built, and Bath 
stone, are among the most durable of these ; but they are all slowly cor- 
roded by exposure to the atmosphere. The chief cause of this corrosion 
appears to be the mechanical disintegration caused by the expansion, in 
freezing, of the water absorbed in the pores of the stone. In order to 
determine the relative extent to which different stones are liable to be 
disintegrated by frost, a test has been devised, which consists in soaking 
the stone repeatedly in a saturated solution of sulphate of soda and allow- 
ing it to dry, when the crystallisation of the salt disintegrates the stone, 
as freezing water would, so that if the particles detached from the surface 
be collected and weighed, a numerical expression for the resistance of the 
material will be obtained. Magnesian limestones (carbonate of lime with 
carbonate of magnesia) are much valued for ornamental architecture, on 
account of the ease with which they may be carved, and are said to be 
more durable in proportion as they approach the composition expressed by 
the formula CaO.C0 2 , MgO.C0 2 .* The magnesian limestone from Bol- 
sover Moor, of which the Houses of Parliament are built, contains 50 per 
cent, of carbonate of lime, 40 of carbonate of magnesia, with some silica 
and alumina. 

It is probable that a slow corrosion of the surface of limestone is effected 
by the carbonic acid continually deposited in aqueous solution from the 
air ; and it is certain that in the atmosphere of towns the limestone is 
attacked by the sulphuric acid which results from the combustion of coal 
and the operations of chemical works. The Houses of Parliament have 
suffered severely, probably from this cause. Many processes have been 
recommended for the preservation of building stones, such as waterproof- 
ing them by the application of oily and resinous substances, and coating or 
impregnating them with solution of soluble glass and similar matters ; but 
none seems yet to have been thoroughly tested by practical experience. 

Purbeck, Ancaster, and Caen stones are well-known limestones employed 
for building. 

303. The mortar employed for building is composed of 1 part of freshly 
slaked lime and 2 or 3 parts of sand intimately mixed with enough water 
to form an uniform paste. The hardening of such a composition appears 
to be due, in the first instance, to the absorption of carbonic acid from 
the air, by which a portion of the lime is converted into carbonate, 
and this, uniting with the unaltered hydrate of lime, forms a solid layer 
adhering closely to the two surfaces of brick or stone, which it cements 
together. In the course of time the lime would act upon the silica, pro- 
ducing silicate of lime, and this chemical action would render the adhesion 
more perfect. The chief use of the sand here, as in the manufacture of 
pottery (p. 405), is to prevent excessive shrinking during the drying of 
the mortar. 

In constructions which are exposed to the action of water, mortars of 
peculiar composition are employed. These hydraulic mortars or cements, 
as they are termed, are prepared by calcining mixtures of carbonate of 

* Any excess of carbonate of lime above that required by this formula may be dissolved 
out by treating the powdered magnesian limestone with weak acetic acid. 



NITRE OR SALTPETRE. 409 

lime with from 10 to 30 per cent, of clay, when the carbonic acid is 
expelled, and the lime combines with a portion of the silicic acid from the 
clay, producing a silicate of lime, and probably also, with the alumina, to 
form aluminate of lime. When the calcined mass is ground to powder 
and mixed with water, the silicates of alumina and lime, and the alumina fce 
of lime, unite to form hydrated double silicates and aluminates, upon 
which water has no action. Roman cement is prepared by calcining a 
limestone containing about 20 per cent, of clay, and hardens in a very 
short time after mixing with water. 

lor Portland cement (so called from its resembling Portland stone) a 
mixture of river mud (chiefly clay) and limestone is calcined at a very 
high temperature. 

Concrete is a mixture of hydraulic cement with small gravel. A speci- 
men of this material from a very ancient Phoenician temple was as hard 
as a rock, and contained nearly 30 per cent, of pebbles. 

Scott? 8 cement is prepared by passing air containing a small quantity of 
sulphurous acid, evolved from burning sulphur, over quick-lime heated to 
dull redness. The setting of this cement appears due to the presence of 
a small proportion of sulphate of lime very intimately mixed with the 
quick-lime. The mixture of these substances yields the cement by a less 
circuitous process. 

GUNPOWDER. 

304. Gunpowder is a very intimate mixture of saltpetre (nitre or 
nitrate of potash), sulphur, and charcoal, which do not act upon each 
other at the ordinary temperature, but when heated together, arrange 
themselves into new forms, evolving a very large amount of gas. 

In order to manufacture gunpowder capable of producing the greatest pos- 
sible effect, great attention is requisite to the purity of the ingredients, the 
process of mixing, and the form ultimately given to the finished powder. 

Chemistry op the Ingredients of Gunpowder — Saltpetre. — Nitrate 
of potash (KN0 3 or K 2 O.N 2 5 ), nitre or saltpetre, is found in some parts 
of India, especially in Bengal and Oude, where it sometimes appears as a 
white incrustation on the surface of the soil, and is sometimes mixed with 
it to some depth. The nitre is extracted from the earth by treating it 
with water, and the solution is evaporated, at first by the heat of the sun, 
and afterwards by artificial heat, when the impure crystals are obtained, 
which are packed in bags and sent to this country as grough (or impure) 
saltpetre. It contains a quantity of extraneous matter varying from 1 to 
10 per cent., and consisting of the chlorides of potassium and sodium, 
sulphates of potash, soda, and lime, vegetable matter from the soil, sand, 
and moisture. The number representing the weight of impurity present 
is usually termed the refraction of the nitre, in allusion to the old method 
of estimating it by casting the melted nitre into a cake and examining its 
fracture, the appearance of which varies according to the amount of foreign 
matter present. 

Peruvian or Chili saltpet re is the nitrate of soda (NaN0 3 or Na 2 O.N 2 5 ) 
found in Peru and Chili in beds beneath the surface soil. It is often spoken 
of as cubical saltpetre, since it crystallises in rhombohedra, easily mistaken 
for cubes, whilst prismatic saltpetre, nitrate of potash, crystallises in six- 
sided prisms. Mtrate of soda cannot be substituted for nitrate of potash as 
an ingredient of gunpowder, since it attracts moisture from the air, becoming 



410 



ARTIFICIAL PRODUCTION OF NITRE. 



damp, and appears to be less powerful in its oxidising action upon com- 
bustible bodies at a high temperature. The Peruvian saltpetre, however, 
forms a very important source from which to prepare the nitrate of potash 
for gunpowder, since it is easily converted into this salt by double decom- 
position with chloride of potassium. The latter salt is now imported in so 
large a quantity from the salt mines of Stassfurth (p. 260), that it enables 
nitrate of soda to be very cheaply converted into nitrate of potash, and 
renders Indian saltpetre of less importance to the manufacturer of gun- 
powder. 

In order to understand the production of saltpetre by the decomposi- 
tion of nitrate of soda with chloride of potassium, it is necessary to be 
acquainted with the solubility of those salts and of the salts produced by 
their mutual decomposition. 



100 parts of boiling water dissolve 
218 parts of nitrate of soda, 

53 , , chloride of potassium, 
200 , , nitrate of potash, 

37 ,, chloride of sodium. 



100 parts of cold water dissolve 
50 parts of nitrate of soda, 
33 ,, chloride of potassium, 
30 „ nitrate of potash, 
36 ,, chloride of sodium. 



It is a general rule that when two salts in solution are mixed, which are 
capable of forming, by exchange of their metals, a salt which is less 
soluble in the liquid, that salt will be produced and separated. 

Thus when nitrate of soda and chloride of potassium are mixed, and 
the solution boiled down, chloride of sodium is deposited, and nitrate of 
potash remains in the boiling liquid — 

NaN0 3 + KC1 - KM), + MaCl. 

When this is allowed to cool, the greater part of the nitrate of potash 
crystallises out, leaving the remainder of the chloride of sodium in solu- 
tion. 

The method usually adopted is to add the chloride of potassium by 
degrees to the boiling solution of nitrate of soda, to remove the chloride 
of sodium with a perforated ladle in proportion as it is deposited, and, 
after allowing the liquid to rest for some time to deposit suspended 
impurities, to run it out into the crystallising pans. 

The potash-salt required for the conversion of nitrate of soda into nitrate 
of potash is sometimes obtained from the refuse of the beet root employed 
in the manufacture of sugar. 

Nitrate of potash is sometimes prepared from the nitrates obtained in 
the nitre-heaps, which consist of accumulations of vegetable and animal 
refuse with limestone, old mortar, ashes, &c. These heaps are constructed 
upon an impermeable clay floor under a shed to protect them from rain. 
One side of the heap is usually vertical and exposed to the prevailing 
wind, the other side being cut into steps or terraces. They are occasionally 
moistened with stable drainings, which are allowed to run into grooves 
cut in the steps at the back of the heap. In such a mass, at an atmo- 
spheric temperature between 60° and 70° F., nitrates of the various bases 
present in the heap are slowly formed, and being dissolved by the 
moisture, are left by it, as it evaporates on the vertical side, in the form 
of an efflorescence. When this has accumulated in sufficient quantity, it 
is scraped off, together with a few inches of the nitrified earth, and 
extracted with water, which dissolves the nitrates, whilst the undissolved 
earth is built up again on the terraced back of the heap. After -two or 



SALTPETRE REFINING. 



411 



Km ■ ■ ■ 
nail 



three years the heap is entirely broken up and reconstructed. The prin- 
cipal nitrates which are found dissolved in the water are those of potash, 
lime, magnesia, and ammonia, the three last of which may be converted 
into nitrate of potash by decomposing them with carbonate of potash. 

The formation of nitric acid in these heaps probably results from che- 
mical changes similar to those which occur in the soils in which nitre 
is naturally formed, but, at present, these changes are not thoroughly 
explained. Some chemists are of opinion that the nitric acid is formed 
by the union of atmospheric nitrogen and oxygen, encouraged by the 
presence of porous solids, and of matters undergoing oxidation. The 
explanation which is best supported by experimental evidence is that 
which refers the formation of nitric acid to the oxidation of ammonia 
(p. 128), evolved by the putrefaction of the nitrogenised matters which 
the heaps contain, this oxidation also being much promoted by the 
presence of the strongly alkaline lime, and of the porous materials capable 
of absorbing ammonia and presenting it under circumstances favourable 
to oxidation. 

In refining saltpetre for the manufacture of gunpowder, the impure salt 
is dissolved in about an equal weight of boiling water in a copper boiler, 
the solution run through cloth filters to remove insoluble matter, and 
allowed to crystallise in a shallow wooden trough lined with copper, the 
bottom of which is formed of two inclined planes (fig. 278). Whilst 
cooling, the solution is kept in continual agitation with wooden stirrers, 
in order that the saltpetre may be deposited in the 
minute crystals known as saltpetre flour, and not in 
the large prisms which are formed when the solution 
is allowed to crystallise tranquilly, and which con- 
tain within them cavities enclosing some of the 
impure liquor from which the saltpetre has been 
crystallised. The saltpetre, being so much less 
soluble in cold than in hot water, is, in great part, 
deposited as the liquid cools, whilst the chlorides 
and other impurities being present in small propor- 
tion, and not presenting the same disparity in their 
solubility at different temperatures, are retained in 
the liquid. The saltpetre flour is drained in a 
wooden trough with a perforated bottom, and trans- 
ferred to a washing-cistern, where it is allowed to 
remain for half an hour in contact with two or three successive small 
quantities of water, to wash away the adhering impure liquor ; it is then 
allowed to drain thoroughly, and in that state, containing from three to 
six per cent, of water, according to the season, is ready to be transferred 
to the incorporating mill or to a hot-air oven, where it is dried if not 
required for immediate use. 

The mother-liquor, from which the saltpetre flour has been deposited, 
is boiled down and crystallised, the crystals being worked up with the 
next batch of grough nitre. The final washings of the flour are returned 
to the boiler in which the grough nitre is originally dissolved. When 
the saltpetre contains very much colouring matter, a little glue or animal 
charcoal is employed by the refiner to assist in its removal. 

The impurities most objectionable in the saltpetre employed for gun- 
powder would be the chlorides of potassium and sodium, which cause it 
to absorb moisture easily from the air ; the chief test, therefore, to which 




Fig. 278. 



412 TESTS FOR PURITY OF SALTPETRE. 

the refiner subjects it, is the addition, to its solution in distilled water, of 
a few drops of solution of nitrate of silver, which causes a milkiness, due 
to the separation of a precipitate of chloride of silver, if the chlorides have 
not been entirely removed. Moreover, the sample should dissolve entirely 
in water, to a perfectly clear colourless solution, which should have no 
effect on blue or red litmus paper, and should give no cloudiness with 
chloride of barium (indicating the presence of sulphates), or with oxalate 
of ammonia (indicating lime), when these are added to separate portions 
of it. Yery minute quantities of sulphates and of lime, such as may have 
been derived from the use of river water in washing the flour, are gene- 
rally disregarded. 

305. Properties of saltpetre. — Nitrate of potash is usually distinguish- 
able by the long striated or grooved six-sided prismatic form in which it 
crystallises (though it may also be obtained in rhombohedral crystals like 
those of nitrate of soda), and by the deflagration which it produces when 
thrown on red-hot coals. It fuses at about 660° F. to a colourless liquid, 
which solidifies on cooling to a translucent brittle crystalline mass. The 
sal prunelle of the shops consists of nitre which has been fused and cast 
into balls. At a red heat it effervesces from the escape of bubbles of 
oxygen, and is converted into nitrite of potash (KN0 2 ), which is itself 
decomposed by a higher temperature, evolving nitrogen and oxygen, and 
leaving a mixture of potash and peroxide of potassium. In contact with 
any combustible body, it undergoes decomposition with great rapidity, 
five-sixths of its oxygen being available for the oxidation of the com- 
bustible substance, and the nitrogen being evolved in the free state ; thus, 
in contact with carbon, the decomposition of the nitre may be represented 
by the equation — 

2(K 2 0.1Sr 2 5 ) + C 5 = 2(K 2 O.C0 2 ) + 3C0 2 + N 4 . 

Since the combustion of a large quantity of material may be thus effected 
in a very small space and in a short time, the temperature produced is 
much higher than that obtained by burning the combustible in the ordi- 
nary way. The specific gravity of saltpetre is 2*07, so that one cubic 
inch weighs 523 grains (obtained by multiplying the weight of a cubic 
inch of water, 252-5 grains by 2*07). Since 202 grains (2 molecules) of 
nitre contain 80 grains (5 atoms) of oxygen available for the oxidation of 
combustible bodies, 523 grains, or one cubic inch, of nitre, would contain 
207 grains or 605 cubic inches of available oxygen, a volume which would 
be contained in about 3000 cubic inches of air • hence, one volume of 
saltpetre represents, in its power of supporting combustion, 3000 volumes 
of atmospheric air. It also enables some combustible substances to burn 
without actual flame, as is exemplified by its use in touchpaper or slow 
port-fire, which consists of paper soaked in a weak solution of saltpetre 
and dried. 

If a continuous design be traced on foolscap paper with a "brush dipped in a solu- 
tion of 30 grains of saltpetre in 100 grains of water, and allowed to dry, it will be 
found that when one part of the pattern is touched with a red-hot iron, it will 
gradually burn its way out, the other portion of the paper remaining unaffected. 

A mixture of 90 grains of saltpetre, 30 of sulphur, and 30 of moderately fine saw- 
dust {Baumes flux) will deflagrate with sufficient intensity to fuse a small silver 
coin into a globule ; the mixture may be pressed down in a walnut shell or a small 
porcelain crucible, and the coin buried in it, the flame of a lamp being applied out- 
side until deflagration commences. 



COMPOSITION OF CHARCOAL. 



413 



Pulvis fulminans is a mixture of 3 parts of saltpetre, 1 part of sulphur, and 2 of 
carbonate of potash, all carefully dried ; when it is heated on an iron plate, no action 
takes place till it begins to melt, when it explodes very violently. 

306. Chaecoal for Gunpowder. — Charcoal has been already described 
as the residue of the destructive distillation of wood, in which process the 
hydrogen and oxygen of the wood are for the most part expelled in the 
forms of wood naphtha (CH 4 0), pyroligneous acid (C 2 H 4 2 ), carbonic 
acid, carbonic oxide, water, &c, leaving a residue containing a much 
larger proportion of carbon than the original wood, and therefore capable 
of producing a much higher temperature (p. 66) by its combustion with 
the saltpetre. The higher the temperature to which the charcoal is 
exposed in its preparation, the larger the proportion of hydrogen and 
oxygen expelled, and the more nearly does the charcoal approach in com- 
position to pure carbon ; but it is not found advantageous in practice to 
employ so high a temperature, since it yields a "dense charcoal of difficult 
combustibility, and therefore less fitted for the manufacture of powder. 

The following table exhibits the composition of dried alder-wood and 
of the charcoal obtained at different temperatures. The incombustible 
matter or ash of the wood and charcoal is here omitted. 



In 100 parts. 


Temperature 
of charring. 


Carbon. 


Hydrogen. 


Oxygen. 


Nitrogen. 


Alder-wood, . . 
Charcoal, . . . 


518° F. 


48-63 
71-0 


5-94 
4-6 


44-75 


0-68 


24-4 




662° 


77-2 


4-1 


18-7 




800° 


82-6 


1-9 


15-5 


5 J 


2000° 


83-3 


23 


14-4 


J? 


2300° 


89-2 


1-4 


9-4 


5 * 


2700° 


95-4 


0-7 


3-9 


5 > 


Above 3000° 


98-8 


0-6 


0-6 



This table shows that at temperatures between 800° and 2000° F., there 
is very little alteration in the composition of the^charcoal, and it is within 
these limits that the charcoal employed for the manfacture of gunpowder 
in this country is prepared. Between these limits, however, the density 
and consequent inflammability of the charcoal vary considerably, that 
prepared at the lower temperatures igniting most readily. Hence it is 
desirable that the temperature of carbonisation should not exceed an 
ordinary low red heat (about 1000° F.) 

The charcoal prepared between 500° and 600° F. has a brown colour 
(charbon roux), and although, it is more easily inflamed than the black 
charcoal obtained at higher temperatures, the presence of so large a pro- 
portion of oxygen so much diminishes its calorific value, that its employ- 
ment in gunpowder is not advantageous. It is used on the Continent in 
the manufacture of sporting-powder, and is prepared by exposing the 
wood, in an iron cylinder, to the action of high-pressure steam heated to 
about 540° F. 

Light woods, such as alder, willow, and dogwood,* are selected for the 
preparation of charcoal for gunpowder, because they yield a lighter and 

* Dogwood charcoal is not made from the true dogwood (comus) but from the alder 
buckthorn (Ehamnus frangnla), commonly called black dogwood. 



414 



SULPHUR FOR GUNPOWDER. 




Fig. 279. — Charcoal retort. 



more easily combustible charcoal, dogwood being employed for the best 
quality of powder for small arms. This wood is chiefly imported, since it 
has not been successfully grown in this country. The wood is stripped of 
its bark, and either exposed for a length of time to the air or dried in a hot 
chamber. Considerable loss of charcoal takes place if damp wood be charred, 
a portion of the carbon being oxidised by the steam at a high temperature. 
In order to convert the wood into charcoal, 1J cwt. of wood is packed 
into a sheet iron cylinder or slip (fig. 279), one end of which is closed 

by a tightly fitting cover, and the 
other by a perforated plate, to 
allow of the escape of the gases and 
vapours expelled during the car- 
bonisation. This cylinder is then 
introduced into a cylindrical cast- 
iron retort, built into a brick fur- 
nace, and provided with a pipe (L) 
for the escape of the products, 
which are usually carried back 
into the furnace (B) to be con- 
sumed. The process of charring 
occupies from 2J to 3J hours, and 
as soon as it is completed, which 
is known by the violet tint of the 
(carbonic oxide) flame from the 
pipe leading into the fire, the slip 
is transferred to an iron box or extinguisher, where the charcoal is allowed 
to cool. About 40 lbs. of charcoal are obtained from the above quantity 
of wood. Charcoal prepared by this process is spoken of as cylinder 
charcoal, to distinguish it from pit charcoal, prepared by the ordinary 
process of charcoal-burning described at p. 62, and which is employed 
for fuze compositions, &c, but not for the best gunpowder. The fitness 
of the charcoal for the manufacture of powder is generally judged of by its 
physical characters. It is of course desirable that the charcoal should be 
as free from incombustible matter as possible. The proportion of the ash 
left by different charcoals varies considerably, but it seldom exceeds two 
per cent. This ash consists chiefly of the carbonates of potash and lime; 
it also contains phosphate of lime, carbonate of magnesia, silicate and sul- 
phate of potash, chloride of sodium, and the oxides of iron and manganese. 
The charcoal is kept for about a fortnight before being ground, for if 
ground when fresh, before it has absorbed moisture from the air, it is 
liable to spontaneous combustion. The grinding is effected in a mill 
resembling a coffee-mill, and the charcoal is afterwards sifted. 

The properties of charcoal have been already described; its great ten- 
dency to absorb moisture from the air is of some importance in the manu- 
facture of gunpowder, from its causing a false estimate to be made of the 
proportion employed, unless the actual amount of water present in the 
charcoal is known. 

Tar charcoal is the name given to sticks of charcoal which have acci- 
dentally become coated with a shining film of carbon left behind by tar 
which has condensed upon it in the retorts; it is sometimes rejected by 
the powder manufacturer. 



307. Sulphur for gunpowder. — Distilled sulphur (p. 189) is the 



MANUFACTURE OF GUNPOWDER. 



415 



variety always employed for the manufacture of gunpowder, the sub- 
limed sulphur being employed for fuze compositions, &c. The alleged 
reason for the preference is that the sublimed sulphur, having been 
deposited in a chamber containing much sulphurous and sulphuric acid 
vapours, its pores have become charged with acid which would be inju- 
rious in the powder ; but it has been pointed out (p. 191) that distilled 
sulphur consists entirely of the soluble or electro-negative variety of sul- 
phur, whilst sublimed sulphur contains a large proportion of the insoluble 
or positive sulphur, which would probably influence its action in gun- 
powder. The sulphur should leave scarcely a trace of incombustible 
matter when burnt, and after stirring the powdered sulphur for some 
time with warm distilled water, the latter should only very feebly redden 
blue litmus. As an ingredient of gunpowder, sulphur is valuable on 
account of the low temperature (560° F.) at which it inflames, thus facili- 
tating the ignition of the powder. Its oxidation by saltpetre appears 
also to be attended with the production of a higher temperature than is 
obtained with charcoal, which would have the effect of accelerating the 
combustion and of increasing, by expansion, the volume of gas evolved. 
The sulphur is ground under edge-runners (fig. 280) and sifted. 

The difference in the inflammability of sulphur and charcoal is strikingly shown 
by heating a square of coarse wire gauze over a flame till it is red-hot in the centre, 
placing it over a jar of oxygen, allowing it to cool till it no longer kindles charcoal- 
powder sprinkled through it from a pepper-box, and whilst the cloud of charcoal is 
still floating in the gas, throwing in sulphur from a second box ; the hot gauze will 
inflame the sulphur, and this will kindle the charcoal. 

An iron rod allowed to cool below redness may be used to stir a mixture of charcoal 
with (3 parts of) nitre ; but if dipped into powdered sulphur, at once inflames it, 
and the flame of the sulphur will kindle the mixture. The effect of the same 
rod upon mixtures of nitre with charcoal alone, and with charcoal and sulphur, is 
instructive. 

The acceleration of the combustion of gunpowder by the sulphur is well shown by 
laying a train, of which one-half consists of a mixture of 75 nitre and 25 charcoal, 
and the other of 75 nitre, 15 charcoal, and 10 sulphur, a red-hot iron being applied 
at the junction of the two trains to start them together. 

308. Manufacture of gunpowder. — The proportions of the ingre- 
dients of gunpowder have been varied 
somewhat in different countries, the 
saltpetre ranging from 74 to 77 per 
cent., the charcoal from 12 to 16, and 
the sulphur from 9 to 12*5 per cent. 
English Government powder contains 
75 per cent, of nitre, 15 per cent, of 
charcoal, 10 percent, of sulphur. An 
extra pound of saltpetre is generally 
added at Waltham, to compensate for 
loss in manufacture. 

The powdered ingredients* are first 
roughly mixed in a revolving gun- 
metal drum, with mixing arms turning 
in an opposite direction, and the mix- 
ture is subjected, in quantities of about 
50 lbs. at a time, to the action of the incorporating mill (fig. 280), where 
it is sprinkled with water, poured through the funnel (F), or from a 

* The amount of water in the moist saltpetre (p. 411) is ascertained by drying and 
melting a weighed sample before the proportions are weighed out. 




Fig. 280. — Incorporating mill. 



416 MANUFACTURE OF GUNPOWDER. 

can with a fine rose, and exposed to trituration and pressure under two 
cast-iron edge-runners (B), rolling round in different paths upon a 
cast-iron bed, a very intimate mixture being thus effected by the 
same kind of movement as in a common pestle and mortar, the 
distribution of the nitre through the mass being also assisted by its solu- 
bility in water. A wooden scraper (C) tipped with copper, prevents the 
roller from getting clogged, and a, plough (D) keeps the mixture in the 
path. Of course, the water employed to moisten the powder must be as 
free from deliquescent salts (especially chlorides, see p. 411) as possible; 
at Waltham condensed steam is employed ; the quantity required varies 
with the state of the atmosphere. The duration of the incorporating 
process is varied according to the kind of powder required, the slow-burn- 
ing powder employed for cannon being sufficiently incorporated in about 
3 hours, whilst rifle-powder requires 5 hours. 

The dark-grey mass of mill-cake which is thus produced, contains 2 or 
3 per cent, of water. It is broken up by passing between grooved rollers 
of gun-metal, and is then placed, in layers of about half an inch thick, 
between copper plates packed in a stout gun-metal box lined inside and 
outside with wood, in which it is subjected for a quarter of an hour to a pres- 
sure of about 70 tons on the square foot, in a hydraulic press, which has 
the effect of condensing a larger quantity of explosive material into a 
given volume, and of diminishing the tendency of the powder to absorb 
moisture from the air and to disintegrate or dust after granulation. The 
press -cake thus obtained is very hard and compact, resembling slate in 
appearance. As far as its chemical nature is concerned, it is finished 
gunpowder, but if it be reduced to powder and a gun loaded with it, the 
combustion of the charge is found to take place too slowly to produce its 
full effect, since the pulverulent form offers so great an obstacle to the 
passage of the flame by which the combustion is communicated from one 
end of the charge- to the other. The press-cake must, therefore, be 
granulated (corned) or broken up into grains of sufficient size to allow the 
rapid passage of the flame between them, and the consequent immediate 
firing of the whole charge. The granulation is effected by crushing the 
press cake between successive pairs of toothed gun-metal rollers, from 
which it falls on to sieves, which separate it into grains of different sizes, 
the dust, or meal powder, passing through the last sieve. At Waltham, 
the R.L.G. (rifle large grain) passes through a sieve of 4 meshes to the 
inch, and is retained on one of 8 meshes, whilst the R.F.G. (rifle fine 
grain) passes through a 12 mesh and is retained on a 20 mesh sieve. 
The granulated powders are freed from dust by passing them through 
revolving cylinders of wooden frame-work covered with canvas or wire 
cloth, and the fine grain powder is glazed by the friction of its own grains 
against each other in revolving barrels. The large-grain powders are 
sometimes glazed or faced with graphite, by introducing a little of that 
substance into the glazing-barrels with the powder. The powder is dried 
in a chamber heated by steam very gradually, so as not to injure the 
grain, and is once more dusted in canvas cylinders before being packed. 

For very large charges, the grains having a diameter of J to -J inch 
(E.L.G.) are found to burn too rapidly, exerting too great a strain upon 
the gun. In such cases, pebble poivder, the grains of which vary from f 
to ^ inch in diameter, is employed. This has been made hitherto by 
breaking up the slabs of press-cake on wooden tables with mallets armed 
with bronze points. 



PROPERTIES OF GUNPOWDER. - 417 

Prismatic powder consists of large grains made of a regular six-sided 
prismatic form by compressing . the powder-meal (without previously 
making it into press-cake) in moulds, with metal punches, whereas the 
pebble powder is irregular in form. The prismatic powder is made with 
perforations in the direction of its length, to facilitate the passage of 
flame through the charge. 

Pellet powder is moulded in a similar manner into cylindrical pellets 
about \ inch long, and f inch in diameter, perforated at one end to about 
the centre. 

309. Properties of gunpowder. — Good gunpowder is composed of 
hard angular grains, which do not soil the fingers, and have a perfectly 
uniform dark-grey colour. Its specific gravity (absolute density) as deter- 
mined by the densimeter* varies between 1 -67 and 1 *84, and its apparent 
density (obtained by weighing a given measure of the grain against an 
equal measure of water) varies from 0'89 to 0'94, so that a cubic foot 
will weigh from 55 to 58 lbs. When exposed to air of average dryness, 
gunpowder absorbs from 0*5 to 1*0 per cent, of water. In damp air it 
absorbs a much larger proportion, and becomes deteriorated in conse- 
quence of the saltpetre being dissolved, and crystallising upon the sur- 
face of the grains. Actual contact with water dissolves the saltpetre and 
disintegrates the grains. When very gradually heated in air, gunpowder 
begins to lose sulphur, even at 212° F., this ingredient passing off rapidly 
as the temperature rises, so that the greater part of it may be expelled 
without inflaming the powder, especially if the powder is heated in 
carbonic acid or hydrogen, to prevent contact with air. If gunpowder 
be suddenly heated to 600° F. in air, it explodes, the sulphur probably 
inflaming first; but out of contact with air a higher temperature is 
required to inflame it. The ignition of gunpowder by flame is not 
ensured unless the flame be flashed among the grains of powder; it 
often takes some time to ignite powder with the flame of a piece of 
burning paper or stick, but contact with a red-hot solid body inflames 
it at once. A heap of good powder, when fired on a sheet of white 
paper, burns without sparks and without scorching or kindling the 
paper, which should exhibit only scanty black marks of charcoal after 
the explosion. If the powder has not been thoroughly incorporated, 
it will leave minute globules of fused nitre upon the paper. Two ounces 
of the powder should be capable of throwing a 68-lb. shot to a distance 
of 260 to 300 feet from an 8-inch mortar at 45° elevation. 

This mode of testing powder by the eprouvette mortar is not now 
applied to Government powders. Far more accurate results are obtained 
by measuring the velocity imparted to a projectile of known weight by a 
given charge of the powder. The velocity is measured by means of a 
chronoscope which registers the distance travelled by the shot in a 
given time by causing it to cut the wire of one electrical circuit at 
the commencement of its flight, and that of another at the conclusion, 
thus telegraphing its velocity to the instrument room at a distance. 

Cannon powder (E.L.G.) is tested by firing a charge of 1 lb. from a 
muzzle-loader rifled gun, with a 12 lb. shot. Small arm powder (E.F.G.) 
is fired from a Snider-Enfield or Martini-Henry rifle. The mean velocity 
at a distance of 105 feet from the muzzle is determined. For E.L.G. it 

* This is a simple apparatus for determining the weight of mercury displaced by a given 
weight of gunpowder from which all the air has been exhausted. 

2 D 



418 PRODUCTS OF EXPLOSION OF GUNPOWDER. 

amounts to about 1000 feet per second. A charge of 70 grs. of B.F.G. 
in the Snider-Enfield rifle gives a velocity somewhat greater than this. 

Very fortunately, it is difficult to explode gunpowder by concussion, 
though it has been found possible to do so, especially on iron, and acci- 
dents appear to have been caused in this way by the iron edge-runners in 
the incorporating mill, when the workmen have neglected the special pre- 
cautions which are laid down for them. The use of stone upon iron in 
the incorporation is avoided, because of the great risk of producing sparks, 
and copper is employed in the various fittings of a powder mill wherever 
it is possible. 

The electric spark is, of course, capable of firing gunpowder, though 
it is not easy to ensure the inflammation of a charge by a spark unless 
its conducting power is slightly improved by keeping it a little moist, 
which may be effected by introduciug a minute quantity of chloride of 
calcium. 

310. Products of explosion of gunpowder. — In the explosion of gun- 
powder, the oxygen of the nitre converts the carbon of the charcoal chiefly 
into carbonic acid (C0 2 ), part of which assumes the gaseous state, whilst 
the remainder combines with the potash of the nitre to form carbonate of 
potash (K 2 O.C0 2 ). The greater part of the sulphur is converted into 
sulphuric acid (S0 3 ), which forms sulphate of potash (K 2 O.S0 3 ). The 
chief part of the nitrogen contained in the nitre is evolved in the uncom- 
bined state. The rough chemical account of the explosion of gunpowder, 
therefore, is that the mixture of nitre, sulphur, and charcoal is resolved 
into a mixture of carbonate of potash, sulphate of potash, carbonic acid, 
and nitrogen, the two last being gases, the elastic force of which, when 
expanded by the heat of the combustion, accounts for the mechanical 
effect of the explosion. 

But in addition to these, several other substances are found among the 
products of the explosion. Thus, the presence of sulphide of potassium 
(K 2 S) may be recognised by the smell of hydrosulphuric acid produced on 
moistening the solid residue in the barrel of a gun, and hydrosulphuric 
acid (H 3 S) itself may often be perceived in the gases produced by the 
explosion, the hydrogen being derived from the charcoal. A little marsh- 
gas (CH 4 ) is also found among the gases, being produced by the decom- 
position of the charcoal, a portion of the hydrogen of which is also 
disengaged in the free state. Carbonic oxide (CO) is always detected 
among the products. It is evident that the collection for analysis of the- 
products of explosion must be attended with some trouble, and that con- 
siderable differences are to be expected between the results obtained by 
different operators, from the variation of the circumstances under which 
the powder is fired and the products collected. When the powder is 
slowly burnt, a considerable proportion of the nitrogen in the saltpetre is 
evolved in the form of nitric oxide gas (NO), which is not found among 
the products of the rapid explosion of powder. 

Some of the most recent experiments upon the explosion of gunpowder 
have been made under conditions very similar to those which occur in 
practice, the powder having been confined in a thin iron case and sus- 
pended in the centre of a strong iron globe exhausted of air, in which the 
powder was fired by electricity, so that the gaseous and solid products of 
the explosion remained within the globe, and could be submitted to 
analysis. Two samples of powder were thus examined, but their com- 



PRODUCTS OF EXPLOSION OF GUNPOWDER. 



419 



position differed from that of English Government powder stated above, 
as will be seen by the following table : — 







I. 


II. 


Nitre, . 




7378 


77-15 


Sulphur, 




12-80 


8-63 


Charcoal, viz. 


, Carbon, . 


10-88 


11-78 




Hydrogen, 


0-38 


0-42 




Oxygen, . 


1-82 


1-79 




Ash, 


0-31 


0-28 



99-97 



100-05 



About 570 grs. of powder were exploded in each experiment. The gas 
collected was found to be inflammable, as would be expected from the 
flash which is always perceived at the muzzle when a gun is discharged. 

100 grs. of sample I. gave 107*4 cub. in. of gas at 32° F. and 30 in. Ear. 

55 55 II- 55 117*0 ,, „ ,, 

The gases contained, in 100 cubic inches — 

Nitrogen 

Carbonic acid (C0 2 ), 
Carbonic oxide (CO), 
Hydrogen, .... 
Sulphuretted hydrogen (H 2 S), 
Marsh-gas (CH 4 ), . 

100-00 100-00 



I. 


II. 


37-58 


35-33 


42-74 


48-90 


10-19 


5-18 


5-93 


6-90 


0-86 


0-67 


2-70 


3-02 



The products of explosion furnished by 100 grains of each powder 
were — 

I. II. 

Sulphate of potash (K 2 O.S0 3 ), 
Carbonate of potash (K 2 O.C0 2 ), 
Hyposulphite of potash (K 2 O.S 2 2 
Sulphide of potassium (K 2 S), 
Sesquicarbonate of ammonia, 
Charcoal, 
Sulphur, 
Nitrogen, 

Carbonic acid (C0 2 ), 
Carbonic oxide (CO), 
Hydrogen, . 

Sulphuretted hydrogen (H 2 S) 
Marsh-gas (CH 4 ), 



36-95 


36-17 


19-40 


20-78 


2-85 


1-77 


0-11 


o-oo 


2-68 


2-66 


2~-67 


2-60 


4-69 


1-16 


9-77 


10-06 


17-39 


21-79 


2-64 


1-47 


o-ii 


0'14 


0-27 


0-23 


0-40 


0-49 



99-83 



99-32 



In both these cases, it will be seen that if the charcoal and sulphur 
which took no part in the combustion be left out of consideration, the 
sulphate and carbonate of potash formed together more than f of the 
solid products of explosion; and that the carbonic acid and nitrogen 
taken together amounted, in the one case to T 9 D , and in the other to |f of 
the gaseous products. If only the chief products of the explosion be 
taken into consideration, viz., sulphate and carbonate of potash, carbonic 
acid, carbonic oxide, and nitrogen, the following equation is the simplest 
which can be constructed from the above numerical data : — 

7(K 2 O.N 2 5 ) + S 4 + C M = 4(K 2 O.S0 3 ) + 3(K 2 O.C0 2 ) + 8C0 2 + N 14 + CO . 



420 



CALCULATION OF THE FORCE OF FTRED GUNPOWDER. 



This equation, however, would re- 
present a gunpowder composed of 

Nitre, 83 -8 

Sulphur 7*5 



Charcoal, 



8-5 



and would require the products of 
decomposition to be — 

Sulphate of potash, . . . 41*2 

Carbonate of potash, . . 24 "5 

Carbonic acid, . . . . 20*8 

Nitrogen, . . . . 11 '6 

Carbonic oxide, . . . 1 '6 



99-7 

Eeasoning from analogy with other chemical operations, it seems pro- 
bable that the explosion of gunpowder really includes a number of 
chemical changes which cannot be simply represented in one equation, 
and that whilst the above equation, or some similar one, represents the 
principal reaction which takes place during the explosion, there are other 
minor reactions in progress, the products of which are found in smaller 
quantity. 

311. Calculation of the force of fired gunpowder. — The mechani- 
cal force exerted in the explosion of gunpowder depends upon the pro- 
duction of a large volume of gas from a small volume of solid, the volume 
of the gas being increased by the expansive effect of the heat generated 
in the combustion of the charcoal and sulphur. To calculate the amount 
of this mechanical force, it is necessary to ascertain the volume of gas 
which would be evolved by a given volume of powder, and the extent to 
which this gas would be expanded by the heat at the instant of explosion. 

In order to illustrate this calculation, let it be assumed that the equa- 
tion given above correctly represents the explosion of the powder, viz. — 

7(K 2 O.N 2 5 ) + S 4 + C 12 = 4(K 2 O.S0 3 ) + 3(K 2 O.C0 2 ) + 8C0 2 + N 14 + CO. 

Now, it is calculated from the Table of Atomic Weights that 



7(K 2 O.N 2 6 ) 



(202 
( 32 
( 12 



Gunpowder, 



7) = 1414 grains. 
4) = 128 ,, 
12) = 144 ,, 

1686 „ 



8CO a 

14N 

CO 



At 60° F., and 30 in. Bar. 
(44 x 8) = 352 grains = 744*0 cub. inches. 
(14 x 14) = 196 ,, = 650-8 
= 28 ,, = 93-0 



1487- 



Hence it appears that 1686 grains of gunpowder would yield 1487 '8 
cubic inches of gas measured at 60° F. and 30 in. barometric pressure. 

If one cubic foot of the powder weighs 58 lbs., one cubic inch will 
weigh 234*9 grains, and will evolve 207 cubic inches of gas measured at 
60° F. and 30 in. Bar.* 

But the mechanical force exerted by the powder depends upon the 
volume of this gas at the period of explosion, and in order to calculate 
this, we must ascertain what would be its temperature at that period. 

A carefully conducted experiment has shown that the explosion of one 
part by weight of gunpowder is able to raise the temperature of 619*5 

* It will be remembered that this is only the apparent density of the powder, as obtained 
by the old method of weighing a cubic foot of the loose powder. The density of a rammed 
down charge would of course be greater than this. 



CALCULATION OF THE FORCE OF FIRED GUNPOWDER. 421 

parts by weight of water from 0° C. to 1° C, or to raise the temperature of 
one part by weight of water from 0° C. to 6 19° -5 C, supposing the water 
to be capable of bearing so great an elevation of temperature without 
change of state. 

This result is generally expressed by saying that the combustion of the 
powder evolves 619*5 units of heat (the unit of heat being the quantity 
required to raise 1 part by weight of water from 0° C. to 1° C.) 

But the products of the explosion of powder will be raised to a higher 
temperature than 619°*5 C, because their specific heat is lower than that 
of water. 

For the purpose of this calculation, the specific heat of a substance may 
be defined as the quantity of heat required to raise 1 gr. of the substance 
through 1° of the thermometer, water being taken as the unit. 

It is evident that if the specific heat of each product of the explosion 
be multiplied by the actual weight of that product, the result will be the 
quantity of heat required to raise that product 1° in temperature. 

The specific heats of the products have been ascertained by experiment, 
and are contained in the first column of figures in the following table. 
The actual weight of each product from the explosion of 1 gr. of powder 
is contained in the second column, and the third column shows the 
quantity of heat required to raise each product 1° C. (representing as 
unity the quantity of heat required to raise 1 gr. of water from 0° C. 
to 1° C.) 





Spec. Heat. 


From 1 gr. 
powder. 


Sulphate of potash, . 


. 0-1901 x 


0-412 = 0-07832 


Car Donate of potash, 


. 0-2162 x 


0-246 = 0-05319 


Carbonic acid, 


. 0-2164 x 


0-209 = 0-04523 


Nitrogen, 


. 0-2440 x 


0-116 = 0-02830 


Carbonic oxide, 


. 0-2479 x 


0-017 = 0-00421 



0-20925 

The quantity of heat, therefore, which is required to raise, through 
1° C, the joint products of the explosion of one grain of gunpowder is 
0*20925 of the above-mentioned unit. 

Dividing the 619*5 units of heat generated in the explosion, by the 
quantity of heat required to raise the joint products through one degree, 
viz., 0*20925, we obtain 2960° C. (= 5328° F.) for the number of de- 
grees through which the products will be raised by the explosion, i.e., for 
the temperature of the products at the moment of explosion.* 

It remains to be ascertained what volume would be occupied, at 5328° 
F., by the 207 cubic inches of gas at 60° F. evolved from one cubic inch 
of powder. 

The expansion which gases suffer when heated amounts to ¥ -^ T of their 
volume at 32° F. for each degree Fahrenheit. 

Thus 491 volumes of gas at 32° F. become 
492 „ „ 33° F., 

and, if heated 28° above 32°, i.e., to 60° F., they would become 491 + 28, 
or 519 volumes. If the 491 volumes be heated to 5328° F., or 5296 c 
above 32°, they will expand to 491 + 5296, or 5787 volumes. 

The volume of the gas at the moment of explosion, therefore, will be 
ascertained from the following proportion — 

* Strictly speaking, 32° F. should be added, on account of the different positions of the 
zero in the two scales, but it would not materially affect the result. 



422 PRESSURE OF FIRED GUNPOWDER. 

Vols, at 60° F. Vols, at 5328° F. Cub. in. at 60° F. Cub. in. a,t 5328° F. 

519 : 5787 : : 207 : 2308 

from which it appears that one cubic inch of powder would evolve a 
quantity of gas measuring 2308 cubic inches at the moment of ex- 
plosion. 

Since the pressure exerted by gases upon the sides of a containing 
space is inversely as their volume, the gas evolved from a cubic inch of 
powder, if developed in a space exactly filled by the powder, would exert 
a pressure of 2308 atmospheres, or 34,620 lbs., or 15J tons upon the 
square inch. 

It is here supposed, of course, that the whole of the gas is evolved at 
once, and is immediately raised to the same temperature, conditions never 
fulfilled in the use of gunpowder in small arms or in cannon, where the 
combustion of the charge is not instantaneous, but rapidly progressive, 
where the confining space is rapidly enlarged by the movement of the 
projectile long before the whole of the charge has exploded, and where 
the heated gas is cooled by contact with the metal of the piece. 

The calculation given above can be regarded only as an illustration of the method, 
as there are several circumstances which vitiate the conclusion arrived at. The 
chemical equation on which it is based is confessedly imperfect. 

"We know little or nothing of the real condition of the products at the moment 
of the explosion ; it is probably very different from that after cooling, when we 
examine them. From what is known of the effect of heat upon carbonic acid and 
carbonic oxide, it is almost certain that these gases are at least partially resolved into 
their elements at the moment of explosion, and it is scarcely likely that the complex 
molecules of sulphate and carbonate of potash would exist at so high a temperature. 
Any breaking up of the molecules of carbonic acid, sulphate and carbonate of potash, 
would increase the expansion, and render the above estimate of the force of fired 
powder too low. 

Again, the specific heats have been stated on the supposition that the gases were 
perfectly unconfined, whereas in the circumstances under which powder is fired, their 
expansion is opposed by the projectile. The subjoined table shows that the specific 
heats of the gases, when restrained from expanding, are much lower :— 





Specific Heats. 




At constant pressure and vary- At varying pressure and con 




ing volume (unconfined). stant volume (confined). 


N 


. 0-2440 . . . 0-1717 


CO 


. 0-2479 . . . 0-1753 


CO, . 


. 0-2164 . . . 0-1702 



Any diminution in the specific heats of the products would obviously increase the 
temperature at the moment of explosion, and therefore the force of the fired powder. 

The actual rate of expansion of gases at so high a temperature is inferred from our 
experience of their behaviour at comparatively low temperatures, and there are some 
indications of a want of agreement under the two conditions. 

The experiments of Andrews have shown that, even at a pressure of 100 atmo- 
spheres, carbonic acid exhibits striking deviations from the law that the pressure 
exerted by a gas is inversely as its volume. 

Noble's experiments, made upon a similar plan to those of Karolyi (p. 418), but 
with much larger charges of powder, and in a vessel provided with a crusher gauge, 
which registers the pressure at the moment of explosion by the compression of a soft 
copper cylinder, indicate the highest pressure of fired powder in a closed space, as 
about 40 tons per square inch. 

_ In criticising all attempts to determine the pressure caused by an explosion, it 
must be remembered that the effects of a given pressure are very different when 
gradually and when suddenly applied, the same amount of force which produces little 
effect as a push, may act very destructively as a blow. 

The period over which the combustion of a given weight of powder 
extends will, of course, depend upon the extent of surface over which it 



EXPLOSION OF POWDER UNDER VARIED CONDITIONS. 423 

can be kindled; thus a single fragment of powder weighing 10 grains, 
even if it were instantaneously kindled over its entire surface, could not 
evolve so much gas in a given time as if it had been broken into ten 
separate grains, each of which was kindled at the same instant, since the 
inside of the large fragment can only be kindled from the outside. Upon 
this principle a given weight of powder in large grains will occupy a 
longer period in its explosion than the same weight in small grains, so 
that the large grain powder is best fitted for ordnance, where the ball is 
very heavy, and the time occupied in moving it will permit the whole of 
the charge to be fired before the ball has left the muzzle, whilst in small 
arms with light projectiles, a finer grained and more quickly burning 
charge is required. If the fine grain powder were used in cannon, the 
whole of the gas might be evolved before the containing space had been 
sensibly enlarged by the movement of the heavy projectile, and the gun 
would be subjected to an unnecessary strain ; on the other hand, a large 
grain powder, in a musket, would evolve its gas so slowly that the ball 
might be expelled with little velocity by the first half of it, and the re- 
mainder would be wasted. There is good reason to believe that even 
under the most favourable circumstances, a large proportion of every charge 
of powder is discharged unexploded from the muzzle of the gun, and is 
therefore wasted. In blasting rocks and other mining operations, the 
space within which the powder is confined is absolutely incapable of en- 
largement until the gas evolved by the combustion has attained sufficient 
pressure to do the whole work, that is, to rend the rock, for example, 
asunder. Accordingly, a slowly burning charge will produce the effect, 
since the rock must give way when the gas attains a certain pressure, 
whether that happens in one second or in ten. Indeed, a slowly burning 
charge is advantageous, as being less liable to shatter the rock or coal, and 
bringing it away in larger masses with less danger. Nitrate of baryta and 
nitrate of soda are sometimes substituted for a part of the nitrate of 
potash in mining powder, its combustion being thus retarded. 

The same charge of the same powder produces very different results when heated 
in different ways. If 5 grs. of gunpowder be placed in a wide test-tube, and fired by 
passing a heated wire into the tube, a slight puff only is perceived ; but if the same 
amount of powder be heated in the tube by a spirit lamp, it will explode with a loud 
report, and perhaps shatter the tube (a copper or brass tube is safer). In the first 
case, the combustion is propagated slowly from the particle first touched by the wire ; 
in the second, all the particles are raised at once to pretty nearly the same tempera- 
ture, and as soon as one explodes, all the rest follow instantaneously. 

When gunpowder is slowly burnt, the products of its decomposition are 
different from those mentioned above ; thus, nitric oxide (NO), arising 
from incomplete decomposition of the nitre, is perceived in considerable 
quantity, and may be recognised by the red colour produced when it is 
brought in contact with air. 

The white smoke resulting from the explosion of gunpowder consists 
chiefly of the sulphate and carbonate of potash in a very finely divided 
state ; it seems probable that at the instant of explosion they are con- 
verted into vapour, and are afterwards deposited in a state of minute 
division as the temperature falls. The fouling or actual solid residue in 
the gun is very trifling when the powder is dry and has been well incor- 
porated ; a damp or slowly burning powder leaves, as might be expected, 
a larger residue. The residue always becomes wet on exposure to air, 
from the great attraction for moisture possessed by the carbonate of potash 
and sulphide of potassium, 



424 EFFECT OF ATMOSPHERIC PRESSURE ON FIRED GUNPOWDER. 



When 10 grains of Walthani Abbey gunpowder are fired in a strong air-tight cylin- 
der, about an inch high, and half an inch in diameter, by the galvanic battery, the 
interior of the cavity is covered with a snow-white powder composed of sulphate and 
carbonate of potash, which deliquesces rapidly in a damp atmosphere. No nitric 
oxide is found in the gas formed by the explosion. 

312. Effect of variations of atmospheric pressure on the combustion of 
gunpowder. — From the circumstance that the combustion of gunpowder is 
independent of any supply of oxygen from the air, it might be supposed 
that it would be as easily inflamed in vacuo as under ordinary atmo- 
spheric pressure. This is not found to be the case, however, for a 
mechanical reason, viz., that the flame from the particles which are first 
ignited escapes so rapidly into the vacuous space, that it does not inflame 
the more remote particles. For a similar reason, charges of powder in 
fuzes are found to burn more slowly under diminished atmospheric 
pressure, the flame (or heated gas) escaping more rapidly and igniting less 
of the remaining charge in a given time. It has been determined that if 
a fuze be charged so as to burn for thirty seconds under ordinary atmo- 
spheric pressure (30 inches barometer), each diminution of one inch in 
barometric pressure will cause a delay of one second in the combustion of 
the charge, so that the fuze will burn for thirty-one seconds when the 
barometer stands at 29 inches. 

The manufacture of gunpowder may be illustrated by the following experiments on 
a small scale : — 

Preparation of the ingredients — Charcoal. — A few small pieces of wood are placed 
in a clay crucible, which is then filled up with dry 
sand and heated in a moderate fire as long as any 
vapours are evolved, when it may be' set aside to 
cool. 

Sulphur. — 500 grains of roll sulphur may be dis- 
tilled in a Florence flask, using another flask, the 
neck of which has been cut off (fig. 281), for a receiver, 
from which the sulphur is afterwards poui-ed, in a 
melted state, upon a piece of tin-plate. 

Nitre. — 1000 grains of impure nitre are dissolved, 
at a moderate heat, in four measured ounces of 
distilled water, in an evaporating dish (fig. 282) ; 
the solution is filtered into a beaker which is placed 
in cold water, and stirred with a glass rod until it 
is quite cold. The saltpetre flour thus obtained is collected upon a filter, thoroughly 
drained, the filter removed from the funnel, spread out, the saltpetre transferred to 
another piece of filter paper, and pressed between 
the paper to remove as much of the liquid as pos- 
sible ; it is then spread out on paper and dried on a 
hot brick. (For the mode of testing its purity see 
p. 412.) 

Mixture of the ingredients. — 60 grains of the char- 
coal, reduced to a very fine powder, 40 grains of the 
sulphur, also previously powdered, and 300 grains of 
the dried nitre, are very intimately mixed in a mortar ; 
50 grains of the mixture are set aside for comparison. 
To the remainder enough water is added to make 
it into a stiff cake, which is well incorporated under 
the pestle for some time. It is then scraped out of 
the mortar and allowed to dry slowly at a very gentle 
heat. When perfectly dry it is crumbled to a coarse 
powder, and the dust sifted out through a piece of wire 
gauze. It will be found instructive to compare, in 
trains and otherwise, the firing of the powder in grains, 
of the dust, and of the mixed ingredients without incorporation, observing especially 
the difference in rapidity of burning and in the amount of residue. 




Fig. 281.— Distillation of 
sulphur. 




Fig. 282. 



CALCULATION OF CALORIFIC VALUE OF FUEL. 425 



CHEMISTEY OF FUEL. 

313. Several of the applications of chemical principles in the combus- 
tion of fuel have been already explained and illustrated. The object of 
this chapter is to compare the chemical composition of the most important 
varieties of fuel, and to exemplify the principles upon which their heating 
power may be calculated from the results furnished by the analysis of the 
fuel. 

All the varieties of ordinary fuel, of course, contain a large proportion 
of carbon, always accompanied by hydrogen and oxygen, and sometimes 
by small proportions of nitrogen and sulphur. Certain mineral substances 
are also contained in all solid fuels, and compose the ash when the fuel is 
burnt. 

For all practical purposes it may be stated, that the amount of heat 
generated by the combustion of a given weight of fuel depends upon the 
weights of carbon and hydrogen, respectively, which enter into combina- 
tion with the oxygen of the air in the act of combustion of the fuel. 

It has been ascertained by experiment that 1 grain of carbon (in the 
form in which it exists in wood charcoal), when combining with oxygen to 
form carbonic acid, produces a quantity of heat which is capable of raising 
8080 grains of water from 0° to 1° of the centigrade thermometer. This 
is usually expressed by saying that the calorific value of carbon is 8080, 
or that carbon produces 8080 units of heat during its combustion to 
carbonic acid. If the fuel, therefore, consisted of pure carbon, it would 
merely be necessary to multiply its weight by 8080 to ascertain its calorific 
value. 

1 grain of hydrogen, daring its conversion into water by combustion, 
evolves enough heat to raise 34,400 grains of water from 0° C. to 1° C, so 
that the calorific value of hydrogen is 34,400. 

If the fuel consisted of carbon and hydrogen only, its calorific value 
would be calculated by multiplying the weight of the carbon in one grain 
of the fuel by 8080, and that of the hydrogen by 34,400, when the sum 
of the products would represent the calorific value. But if the fuel 
contains oxygen already combined with it, the calorific value will be 
diminished, since this oxygen will consume a part of the combustible 
without generating heat, because it already exists in a state of combina- 
tion with the carbon and hydrogen of the fuel. For example, 1 grain of 
wood contains 0'5 grain of carbon, 0'06 of hydrogen, and 0'44 of oxygen. 
Now, oxygen combines with one-eighth of its weight of hydrogen to 
form water, so that the 0*44 grain of oxygen will convert '44 -r- 
8 = -055 of the hydrogen into water, without evolution of available 
heat, leaving only 0*005 available for the production of heat. The 
calorific value of the wood, therefore, would be represented by the sum of 
0-005 x 34,400 (=172) and 0-5 x 8080 ( = 4040), which would amount 
to 4212 ; or 1 grain of wood should raise 4212 grains of water from 
0° C. to 1° C. 

These considerations lead to the following general formula for calculat- 
ing the calorific value of a fuel containing carbon, hydrogen, and oxygen, 
where c, h, and o respectively represent the carbon, hydrogen, and oxygen 
in one grain of fuel. 

The calorific value (or number of grains of water which might be heated 



426 CALCULATION OF CALOJRIFIC INTENSITY OF FUEL. 



by the fuel from 0° C. to 1° C.) = 8080 c + 34,400 (h - ~ ) or 



(*-0 



8080 c + 34,400 h - 4300 o. 

The calorific value of a fuel, as determined by experiment, is generally 
less than would be calculated from its chemical composition, in consequence 
of the absorption of a certain amount of heat attending the chemical 
decomposition of the fuel. In the case of compounds of carbon and hydro- 
gen, it has been observed that even when they have the same composition 
in 100 parts, they have not of necessity the same calorific value, the latter 
being affected by the difference in the arrangement of the component par- 
ticles of the compound, which causes a difference in the quantity of heat 
absorbed during its decomposition. Thus olefiant gas (C 2 H 4 ) and cetylene 
(C 16 H 32 ) have the same percentage composition, and their calculated calorific 
values would be identical, but the former is found to produce 11,858 units 
of heat, and the latter only 11,055. As a general rule, however, it is found 
that the calorific values of the hydrocarbons which contain a multiple of 
CH 2 , agree more nearly with the calculated numbers than do those of 
hydrocarbons which belong to the marsh- gas series. 

It must be remembered that the calorific value of a fuel represents the 
actual amount of heat which a given weight of it is capable of producing, 
and is quite independent of the manner in which the fuel is burnt. Thus, 
a hundredweight of coal will produce precisely the same amount of heat in 
an ordinary grate as in a wind-furnace, though in the former case the fire 
will scarcely be capable of melting copper, and in the latter it will melt 
steel. The difference resides in the temperature or calorific intensity of 
the two fires ; in the wind-furnace, through which a rapid draught of air 
is maintained by a chimney, a much greater weight of atmospheric oxygen 
is brought into contact with the fuel in a given time, so that, in that 
time, a greater weight of fuel will be consumed and more heat will be 
produced ; hence the fire will have a higher temperature, for the tem- 
perature represents, not the quantity of heat present in a given mass of 
matter, but the intensity, or extent to which that heat is accumulated at 
any particular point. In the case of the wind-furnace here cited, a further 
advantage is gained from the circumstance, that the rapid draught of air 
allows a given weight of fuel to be consumed in a smaller space, and, of 
course, the smaller the area over which a given quantity of heat is distri- 
buted, the higher the temperature within that area (as exemplified in the 
use of the common burning-glass). In some of the practical applications, 
of fuel, such as heating steam-boilers and warming buildings, it is the 
calorific value of the fuel which chiefly concerns us, but the case is different 
where metals are to be melted, or chemical changes to be brought about 
by the application of a very high temperature, for it is then the calorific 
intensity, or actual temperature of the burning mass, which has to be con- 
sidered. No trustworthy method has yet been devised for determining 
by direct experiment the calorific intensity of fuel, and it is therefore 
ascertained by calculation from the calorific value. 

Let it be required to calculate the calorific intensity, or actual tempera- 
ture, of carbon burning in pure oxygen gas. 

12 grains of carbon combine with 32 grains of oxygen, producing 44 
trains of carbonic acid; hence 1 grain of carbon combines with 2*67 
grains of oxygen, producing 3*67 grains of carbonic acid. It has been 
seen above that 1 grain of carbon evolves 8080 units of heat, or is capable 



CALCULATION OF CALORIFIC INTENSITY OF FUEL. 427 

of raising 8080 grains of water from 0° to 1° C, or, on the supposition 
*hat the water would bear such an elevation of temperature, the 1 grain 
of carbon would raise 1 grain of water from 0° to 8080° C. If the specific 
heat (or heat required to raise 1 grain through 1°, see p. 421) of carbonic 
acid were the same as that of water, 8080° divided by 3*67 would repre- 
sent the temperature to which the 3 "67 grains of carbonic acid would be 
raised, and therefore the temperature to which the solid carbon producing 
it would be raised in the act of combustion. But the specific heat of 
carbonic acid gas is only 0*2163, so that a given amount of heat would 
raise 1 grain of carbonic acid to nearly five times as high a temperature 
as that to which it would raise 1 grain of water. 

Dividing the 8080 units of heat (available for raising the temperature 
of the carbonic acid) by 0*2163, the quantity of heat required to raise 1 
grain of carbonic acid 1°, we obtain 37,355 for the number of degrees 
through which 1 grain of carbonic acid might be raised by the combustion 
of 1 grain of carbon. But there are 3 '6 7 grains of carbonic acid formed 
in the combustion, so that the above number of degrees must be divided 
by 3 67 in order to obtain the actual temperature of the carbonic acid at, 
the instant of its production, that is, the temperature of the burning mass. 
The calorific intensity of carbon burning in pure oxygen is, therefore, 
(37,355° C.- 3-67 = ) 10,178° C. or 18,352° F. But if the carbon be 
burnt in air, the temperature will be far lower, because the nitrogen of 
the air will absorb a part of the heat, to which it contributes nothing. 
The 2 '6 7 grains of oxygen required to burn 1 grain of carbon would be 
mixed, in air, with 8' 9 3 grains of nitrogen, so that the 8080 units of 
heat would be distributed over 3*67 grains of carbonic acid and 8*93 
grains of nitrogen. Since the specific heat of carbonic acid is 0*2163, 
the product of 3*67 x 0*2163 (or 0*794) represents the quantity of heat 
required to raise the 3*67 grains of carbonic acid from 0° to 1° C. 

The specific heat of nitrogen is 0*2438 ; hence 8*93 x 0*2438 (or 2*177) 
represents the quantity of heat required to raise the 8*93 grains of atmo- 
spheric nitrogen from C to 1° C. 

Adding together these products, we find that 0*794 + 2*177 = 2*971 
represents the quantity of heat required to raise both the nitrogen and 
carbonic acid from 0° to 1° C. 

Dividing the 8080° by 2*971, we obtain 2720° C. (4928° F.) for the 
number of degrees through which these gases would be raised in the com- 
bustion, i.e., for the calorific intensity of carbon burning in air. By heat- 
ing the air before it enters the furnace (as in the hot-blast iron furnace), 
of course the calorific intensity would be increased ; thus if the air be 
introduced into the furnace at a temperature of 600° F., it might be stated, 
without serious error, that the temperature producible in the furnace 
would be 5528° F. (4928° + 600°). The temperature might be further 
increased by diminishing the area of combustion, as by employing very 
compact fuel and increasing the pressure of the blast 

In calculating the calorific intensity of hydrogen burning in air, from 
its calorific value, it must be remembered that in the experimental deter- 
mination of the latter number, the steam produced in the combustion was 
condensed to the liquid form, so that its latent heat was added to the 
number representing the calorific value of the hydrogen ; but the latent 
heat of the steam must be deducted in calculating the calorific intensity, 
because the steam goes off from the burning mass and carries its latent 
heat with it. 



428 CALCULATION OF CALORIFIC INTENSITY OF FUEL. 

1 grain of hydrogen, burning in air, combines with 8 grains of oxygen, 
producing 9 grains of steam, leaving 26*77 grains of atmospheric nitrogen, 
and evolving 34,400 units of heat. 

It has been experimentally determined that the latent heat of steam is 
537° C, that is, 1 grain of water, in becoming steam, absorbs 537 units 
of heat (or as much heat as would raise 537 grains of water from 0° to 1° 
C.) without rising in temperature as indicated by the thermometer. The 
9 grains of water produced by the combustion of 1 grain of hydrogen will 
absorb, or render latent, 537 x 9 = 4833 units of heat. Deducting this 
quantity from the 34,400 units evolved in the combustion of 1 grain of 
hydrogen, there remain 29,567 units of heat available for raising the tem- 
perature of the 9 grains of steam and 26*77 grains of atmospheric nitrogen. 
The specific heat of steam being 0*480, the number (0*480 x9 = ) 4*32 
represents the quantity of heat required to raise the 9 grains of steam 
through 1° C. ; and the specific heat of nitrogen (0*2438) multiplied by 
its weight (26*77 grains), gives 6*53 units of heat required to raise the 
26*77 grains of nitrogen through 1° C. By dividing the available heat 
(29,567 units) by the joint quantities required to raise the steam and nitro- 
gen through 1° C. (4*32 + 6*53 = 10*85), we obtain the number 2725° C. 
(4937° F.) for the calorific intensity of hydrogen burning in air. 

The method of calculating the calorific intensity of a fuel composed of carbon, 
hydrogen, and oxygen, will now be easily followed. 

Let c and h respectively represent the weights of carbon and hydrogen in 1 gr. 

of fuel, and o that of the oxygen. Then ~ = weight of hydrogen required to convert 

o 
the oxygen into water, and 7i - ^ represents the hydrogen which is available for the 



production of heat. / 

"(*-D 



8080 c + 34,400 (A - 5 ) represents the 



calorific value in °C, = 8080 c + 34,400 h - 4300 0. 
2 '67 c = atmospheric oxygen consumed by the carbon ; 

S\h- - ) or 8 h - = atmospheric oxygen consumed by the hydrogen available 
* 8 

as fuel. 

3-34 (2*67 c + 8 h - 0) = atmospheric nitrogen = 8*92 c + 26'72/e. - 3*34 0. 

Multiplying this by the specific heat of nitrogen 0*2438, we obtain — 
2*17 c + 6*51 h - 0*81 for the heat required to raise the nitrogen through 1° C. 

0*794 c represents the quantity of heat required to raise the carbonic acid through 
1° C, and 4*32 h is the heat required to raise the steam through 1°. Accordingly, 
the available heat, 8080 c + 34,400 h - 4300 0, must be divided by 0*794 c + 4*32 h 
+ (2*17 c + 6-51 h - 0*81 0), or 2*96 c + 10*83 h - 0*81 in order to obtain the 
calorific intensity. 

Hence, the calorific intensity, in centigrade degrees, of a fuel composed of carbon, 
hydrogen, and oxygen, is represented by the formula — 

8080 c + 3 1, 400 h - 4300 ■ 
2*96 c + 10*83 h - 0*81 0. 

The actual calorific intensity of the fuel is not so high as it should be 
according to theory, because a part of the carbon and hydrogen is con- 
verted into gas by destructive distillation of the fuel, and this gas is not 
actually burnt in the fire, so that its calorific intensity is not added to 
that of the burning solid mass. Again, a portion of the carbon is con- 



COMPOSITION AND VALUE OF FUELS. 



429 



verted into carbonic oxide (CO), especially if the supply of air be imperfect, 
and much, less heat is produced than if the carbon were converted into 
carbonic acid ; although it is true that this carbonic oxide may be con- 
sumed above the fire by supplying air to it, the heat thus produced does 
not increase the calorific intensity or temperature of the fire itself. 

One grain of carbon furnishes 2 "33 grains of carbonic oxide. These 2 -33 
grains of carbonic oxide evolve, in their combustion, 5599 units of heat. 
But if the 1 grain of carbon had been converted at once into carbonic 
acid, it would have evolved 8080 units of heat, so that 8080 — 5599, or 
2481, represents the heat evolved during the conversion of 1 grain of 
carbon into carbonic oxide, showing that a considerable loss of heat in the 
fire is caused by an imperfect supply of air. It has been already pointed 
out, in the section relating to Coal, that the formation of carbonic oxide is 
sometimes encouraged with a view to the production of a flame from non- 
flaming coal, such as anthracite. 

The following table exhibits the average percentage composition of the 
principal varieties of fuel (exclusive of ash), together with their calculated 
calorific values and intensities. 





Carbon. 


Hydrogen. 


Oxygen. 


Nitrogen. 


Sulphur. 


Calorific 

Value. — Intensity. 


Wood (Oak), . 


50-18 


6-08 


43-74 






4212° C. 


2380° C. 


Peat, .... 


61-53 


5-64 


32-82 






5654 


2547 


Lignite (Bovey), 


67-86 


5-75 


23-39 


0-57 


2-41 


6569 


2628 


Bituminous coal, 


79-38 


5-34 


13-01 


1-85 


0-39 


7544 


2694 


Charcoal, . . . 


90-44 


2-91 


6-63 






8003 


2760 


Anthracite, . . 
Coke, .... 


91-86 
97-32 


3-33 

0-49 


3-02 


0-84 


0-92 


8337 
8009 


2779 
2761 


2-17 



In all ordinary fires and furnaces, a large amount of heat is wasted in 
the current of heated products of combustion escaping from the chimney. 
Of course, a portion of this heat is necessary in order to produce the 
draught of the chimney. In boiler furnaces it is found that, for this pur- 
pose, the temperature of the air escaping from the chimney must not be 
lower than from 500° to 600° F. If the fuel could be consumed by sup- 
plying only so much air as contains the requisite quantity of oxygen, a 
great saving might be effected, but in practice, about twice the calculated 
quantity of air must be supplied, in order to effect the removal of the 
products of combustion with sufficient rapidity. 

Much economy of fuel may be expected from the use of furnaces con- 
structed on the principle of Siemens' regenerative furnace, in which the 
waste heat of the products of combustion is absorbed by a quantity of 
fire-bricks, and employed to heat the air before it enters the furnace, two 
chambers of fire-bricks doing duty alternately, for absorbing the heat from 
the issuing gas, and for imparting heat to the entering air, the current 
being reversed by a valve as soon as the fire-bricks are strongly heated. 

(For the principles of smoke prevention, and other particulars of the 
chemistry of fuel, see Coal.) 



ORGANIC CHEMISTRY. 



314. Although, it is impossible to propose a definition of the term 
organic substance which shall not be applicable to some of the substances 
commonly regarded as inorganic, it is found advantageous for the purposes 
of study to treat organic chemistry as a separate division of the science, 
dealing especially with those substances which are usually obtained, 
either directly or indirectly, from animals and vegetables. 

One very important distinction between organic and inorganic substances 
is, that the former are for the most part composed of carbon, hydrogen, 
nitrogen, and oxygen, in different proportions and in various modes of 
arrangement, and that they are, therefore, much more frequently con- 
vertible into each other by metamorphosis, without extraneous addition 
of matter, than inorganic substances are. 

It has been already pointed out that the chemist is gradually 
learning to produce, though by somewhat clumsy and circuitous processes, 
many of the substances which were formerly believed incapable of being 
formed, except through the intervention of life ; but no substance possess- 
ing an organised, structure, such as woody fibre or muscular fibre, and no 
absolutely indispensable organic constituent of animal or vegetable frames, 
has yet been artificially procured. 

It will not escape notice that the four elements which compose the 
greater number of organic substances, viz., hydrogen, oxygen, nitrogen, 
and carbon, are, respectively, monatomic, diatomic, triatomic, and tetra- 
tomic elements (p. 158),' and are, therefore, capable of forming a greater 
variety of compounds than would be the case if they were elements of 
equal atomicities. 

In the following pages, no strictly scientific classification of organic 
substances has been adopted, since it would often render it necessary to 
describe, in separate sections, substances which are, in nature, closely con- 
nected with each other, but an empirical arrangement has been followed, 
so that the reader may find his memory assisted and the interest of the 
subject sustained, by being enabled to bring the facts and explanations 
into immediate connection with familiar processes of ordinary life.* 

One of the most conspicuous substances standing upon the boundary 
between organic and inorganic chemistry is the compound of carbon and 
nitrogen known as cyanogen, which is intimately connected with inorganic 
substances through some of the processes for its production, and through 
its similarity to the chlorine group of elements, whilst the origin and 

* The number of organic substances known to the chemist is so great that a mere list of 
them would occupy a volume. In the present work a selection has been made of those 
which are interesting for their practical applications or instructive from theoretical con- 
siderations. 



HISTORY OF CYANOGEN. 431 

chemical properties of a large number of its compounds give them a claim 
to be ranked among organic substances. The study of this substance, 
therefore, will form a fit introduction to organic chemistry. 

CYANOGEN AND ITS COMPOUNDS. 

315. In the beginning of the last century, a manufacturer of colours at 
Berlin accidentally obtained a blue powder when precipitating sulphate of 
iron with potash. This substance was used as a colour, under the name 
of Prussian blue, for several years, before any explanation of its production 
was attempted, or even before the conditions under which it was formed 
were exactly determined. In 1724 it was shown that Prussian blue could 
be prepared by calcining dried animal matters with carbonate of potash, 
and mixing the aqueous solution of the calcined mass, first with sulphate 
of iron and afterwards with hydrochloric acid ; but the most important step 
towards the determination of its composition was made by Macquer, who 
found that by boiling it with an alkali, Prussian blue was decomposed, 
yielding a residue of red oxide of iron, and a solution which reproduced 
the blue when mixed with a salt of iron, from which he inferred that the 
colour was a compound of the oxide of iron with an acid for which the 
alkali had a more powerful attraction, — a belief confirmed, in 1782, by 
Scheele's observations, that when an alkaline solution prepared for mak- 
ing the blue was exposed to the air, or to the action of carbonic acid, it 
lost the power of furnishing the colour, but the escaping vapour struck a 
blue on paper impregnated with oxide of iron. Scheele also prepared this 
acid in a pure state, and it soon after obtained the name oi prussic acid. 

In 1787 Berthollet found prussic acid to be composed of carbon, 
hydrogen, and nitrogen, but he also showed that the power of the alka- 
line liquor to produce Prussian blue depended upon the presence of a 
yellow salt crystallising in octahedra, and containing prussic acid, potash, 
and oxide of iron, though the latter was so intimately bound up with the 
other constituents, that it could not be separated by those substances 
which are usually employed to precipitate iron. 

Porrett, in 1814, applying the greatly increased resources of chemistry 
to the investigation of this subject, decomposed Prussian blue with baryta, 
and subsequently removed the baryta from the salt thus obtained by 
means of sulphuric acid, when he obtained a solution of the acid, which 
he named fervuretted chyazic acid. 

In 1815, Gay-Lussac, having boiled Prussian blue (or prussiate of iron, 
as it was then called) with red oxide of mercury and water, and crystal- 
lised the so-called prussiate of mercury, exposed it, in the dry state, to the 
action of heat, and obtained a gas, having the composition CN, which 
was called cyanogen* in allusion to its connection with Prussian blue. It 
was then seen that the substance which had been called ferruretted chyazic 
acid contained iron and the elements of cyanogen, whence it was called 
ferrocyanic acid, and its salts were spoken of as ferrocyanates. Eobiquet 
first obtained this acid in the crystallised state, having the composition 
C 6 H 4 N 6 Fe ; and since it was found that, when brought in contact with 
metallic oxides, it exchanged the H 4 for an equivalent quantity of the 
metal, according to the equation — 

H 4 .C 6 N 6 Fe + 2M ,/ = M 2 ".C 6 N 6 Fe + 2H 2 , 

* From Kvaveos, blue. 



432 YELLOW PRUSSIATE OF POTASH. 

it was concluded that the CglSTgFe composed a distinct group or radical, 
which was named ferrocyanogen, the acid being called hydroferrocyanic 
acid, and the salts ferrocyanides. 

316. Prussiate of potash. — The yellow prussiate of potash or ferro- 
cyanide of potassium (K 4 C 6 ISr 6 Fe.3Aq.) is manufactured upon a large scale 
by a process which is the more interesting because it turns to account 
some of the commonest kinds of refuse, such as old leather, hoof parings, 
blood, and, in short, any animal matter rich in nitrogen, and not appli- 
cable to any more economical purpose. Sometimes these substances are 
first subjected to destructive distillation for the carbonate of ammonia 
which they are capable of yielding, and the residual highly nitrogenised 
charcoal is then used for the production of the ferrocyanide of potassium. 
Such matters are fused in an iron vessel with carbonate of potash and iron 
filings, and the fused mass is heated with water in open boilers, when a 
yellow solution is obtained, which, after evaporation, deposits truncated 
pyramidal crystals of ferrocyanide of potassium, containing 3 molecules 
of water. 

The theory of this process has been elucidated by the researches of 
Liebig. If carbonate of potash be strongly heated in contact with 
pure carbon, there result (page 259) carbonic oxide and potassium, 
K 2 O.C0 2 + C 2 = 3CO + K 2 j but if the carbon be associated with nitrogen, 
the reduction will be effected at a much lower temperature, and the potas- 
sium will combine with an atom of carbon and an atom of nitrogen, to 
form the cyanide of potassium (KCN). When this salt, dissolved in 
water, is heated with metallic iron in the presence of air, oxygen is 
absorbed, and the iron dissolved to form ferrocyanide of potassium — ■ 

6KC2n t + Fe + = K 4 .C 6 N 6 Fe + K 2 . 

The oxygen may also be acquired from, the water, an equivalent quantity 
of hydrogen being evolved. 

Prussian blue. — For the preparation of Prussian blue it is usual to 
mix solutions of ferrocyanide of potassium and persulphate of iron, when 
the blue is precipitated, having been produced according to the equation — 

3K 4 Fcy + 2(FeA.3S0 3 ) = 6(K 2 O.S0 3 ) + Fe 4 Fcy, , 

3S8 Prussians. 

in which the symbol Fey represents the group C 6 N 6 Fe (ferrocyanogen), 
which is capable of playing the same part in many decompositions as if 
it were an elementary substance. This compound radical has never yet 
been obtained in the separate state, but it can be traced through a com- 
plete series of compounds, in which it exactly resembles chlorine in its 
chemical relations • thus the hydroferrocyanic acid (H 4 Fcy), and the fer- 
rocyanides of the metals, are perfectly analogous to hydrochloric acid and 
the chlorides, though containing a compound radical instead of a simple 
one ; but whereas chlorine is a monatomic radical, combining only with 1 
atom of hydrogen, ferrocyanogen is tetratomic • and hence Prussian blue, 
the sesauiferrocyanide of iron, has the composition Fe/'Tcy/*, whilst the 
sesquichloride is Fe/"C1/. When Prussian blue is prepared by pouring 
solution of persulphate of iron into an excess of ferrocyanide of potassium, 
it is found that, as soon as the excess of the latter has been washed away, 
the precipitate dissolves in pure water, forming what is used by dyers 
under the name of soluble Prussian blue. Oxalic acid is capable of dis- 
solving the blue, and this solution forms the basis of ordinary blue ink. 






PKUSSIAN BLUE. 433 

Prussian blue is sometimes prepared with the green protosulphate of 
iron (FeO.SOJ, but in that case it is necessary to expose the precipitate 
for some time to the air, since the first result is a nearly white precipitate 
which may be regarded as a double ferrocyanide of iron and potassium 
(K 4 Fcy,Fe 2 Fcy). 

2(K 4 Fcy) + 2(FeO.SCQ = 2(K 2 O.S0 3 ) + K 4 Fcy.Fe 2 Fcy. 

When this precipitate is exposed to the air, it gradually acquires a dark-blue 
colour, becoming eventually converted into Prussian blue by oxidation — 

3(K 4 Fcy.Fe 2 Fcy) + 3 = 3K 4 Fcy + Fe 2 3 + Fe 4 Fcy 3 . 

Prussian blue is easily decomposed by alkalies, a brown residue of ses- 
quioxide of iron being left, Fe 4 Fcy 3 + 12KHO = 3K 4 Fcy + 2Fe. 2 3 + 6H 2 0. 
This decomposition is turned to account by the calico-printer for pro- 
ducing a buff or white pattern upon a blue ground. The stuff having 
been dyed blue by passing, first through a solution of a per-salt of iron, 
and afterwards through one of ferrocyanide of potassium, the pattern is 
discharged by an alkali, which leaves the brown peroxide of iron capable 
of being removed by a dilute acid, when the stuff has been rinsed, so as to 
leave the design white. 

Hydroferrocyanic acid. — By decomposing a cold saturated solution of 
the ferrocyanide of potassium with about an equal volume of hydrochloric 
acid, colourless crystals of hydroferrocyanic acid (H 4 Fcy) are obtained, 
which are insoluble in hydrochloric acid, but readily soluble in water. 
When a solution of this acid is heated, it evolves hydrocyanic acid (HCN), 
and deposits a white precipitate of cyanide of iron Fe(CN) 2 which be- 
comes blue on exposure to the air, being converted into Prussian blue ; 
the simplest way of explaining this, as well as many other decompositions 
of hydroferrocyanic acid r,nd the ferrocyanides, is to view the radical 
ferrocyanogen as formed by the union of six molecules of cyanogen (CN) 
and one atom of iron, when hydroferrocyanic acid becomes H 4 .Cy 6 Fe, and 
Prussian blue Fe 4 .3Cy 6 Fe.* 

The decomposition of the hydroferrocyanic acid by heat would then be 
represented by the equation — 

H 4 .Cy 6 Fe = 4HCy + FeCy 2 , 

Hydroferrocyanic Hydrocyanic Protocyanide 

acid. acid. of iron. 

and the formation of Prussian blue from this last compound on exposure 
to air — 

9FeCy 2 + 3 = Fe 4 .3Cy 6 Fe + Fe 2 3 . 

Prussian blue. 

Hydrocyanic or prussic acid. — Advantage is taken of the decomposition 
of the ferrocyanide of potassium by acids, in the preparation of solution 
of hydrocyanic acid for medicinal use. For this purpose, 2 parts of the 
ferrocyanide of potassium in powder are distilled with 1J parts of oil of 
vitriol diluted with 2 parts of water, the vapour of hydrocyanic acid 
being carefully condensed (see fig. 47). The change is represented by 
the equation — 

2K 4 (Cy ? Fe) + 3(H 2 O.S0 3 ) = 3(K 2 O.S0 3 ) + K 2 Fe(Cy 6 Fe) + 6HCy. 

Ferrocyanide of Ferrocyanide of Hydrocyanic 

potassium. iron and potassium. acid. 

* Since Cy' is monatomic, Cy/Fe" should be tetratonric. 

2 E 



434 HYDROCYANIC OR PRUSSIC ACID. 

There is left in the retort a pale greenish salt, which rapidly becomes blue 
when exposed to the air, and is probably identical with the double ferro- 
cyanide of potassium and iron produced when protosulphate of iron is 
decomposed by ferrocyanide of potassium (p. 433). 

The solution of hydrocyanic acid thus obtained is colourless, and 
exhales the remarkable odour of the acid ; its acid characters are very 
feeble indeed, even more so than those of carbonic acid, but it is extremely 
poisonous, a very small dose destroying life almost immediately. Hydro- 
cyanic acid is found in laurel-water, and in water distilled from the kernels 
of many stone-fruits, such as the peach, apricot, and plum. In minute doses 
hydrocyanic acid is a very valuable remedy, and is employed in medicine 
in solutions of different strengths. One of these, which is known as the 
acid of the London Pharmacopoeia, contains 2 per cent, of hydrocyanic 
acid, and is prepared by the process mentioned above. Seheele's acid 
varies in strength, but usually contains between 4 and 5 per cent, of true 
hydrocyanic acid. This acid is prepared from Prussian blue, by the 
process originally employed by Scheele when the acid was discovered. 
It consists in boiling Prussian blue with water and red oxide of mercury, 
until the blue colour disappears ; peroxide of iron is separated, and 
cyanide of mercury (HgCyJ passes into solution ; the latter is filtered, 
mixed with diluted sulphuric acid, and shaken with iron-filings, which 
precipitate the mercury in the metallic state, leaving free hydrocyanic 
acid in the liquid, which is then distilled — 

HgCy 2 + Fe + H 2 O.S0 3 = 2HCy + FeO.S0 3 + Hg. 

In order clearly to understand this process, it must be known that the 
mercury exhibits a special tendency to combine with cyanogen, which is 
sufficiently powerful, in this instance, to bring about the decomposition 
of the ferrocyanogen existing in the Prussian blue, a part of the cyanogen 
being exchanged for the oxygen of the oxide of mercury. 

It is from the cyanide of mercury that the pure anhydrous hydrocyanic 
acid and cyanogen itself are prepared. For these purposes, it may be 
obtained by dissolving the red oxide of mercury in hydrocyanic acid, 
when a double decomposition takes place, exactly as with hydrochloric 
acid, HgO + 2HCy = IJgCy 2 + H 2 0, and the cyanide of mercury is 
obtained in square prismatic crystals on evaporating the solution. If 
these crystals be dried and gently warmed with strong hydrochloric 
acid, chloride of mercury will be formed, and hydrocyanic acid evolved, 
HgCy 2 + 2HC1 = HgCl 2 + 2HCy. The mixed vapours of hydrochloric and 
hydrocyanic acid are passed over fragments of marble (CaO.C0 2 ), which 
absorb the hydrochloric acid (CaO.C0 2 + 2HC1 = CaCl 2 + H 2 + C0 2 ), 
but not the hydrocyanic, since the latter is too weak an acid even to 
displace carbonic acid. The mixture of hydrocyanic and carbonic acids 
is passed over chloride of calcium to remove aqueous vapour, and after- 
wards through a tube cooled in a mixture of ice and salt, when the 
hydrocyanic acid is condensed to a colourless liquid, which evaporates so 
rapidly when exposed to the air that it lowers the temperature to the 
freezing point of the acid, which is about 0° F. ; at a little above the 
ordinary temperature (79° F.) it boils, and emits a vapour which burns 
with a blue flame. When kept for some time it is liable to undergo a 
spontaneous decomposition, evolving ammonia, and being converted into 
a brown mass of uncertain composition. The aqueous solution of the 
acid suffers a similar change, and since exposure to light favours the 



PREPARATION OF CYANOGEN. 435 

decomposition, the medicinal acid is usually kept in bottles covered with 
paper. The presence of a very small quantity of sulphuric acid prevents 
this change, and hence the acid prepared by distilling ferrocyanide of 
potassium with sulphuric acid, which usually contains traces of the latter, 
can be preserved much better than that prepared by other methods. 

"When hydriodic acid gas is passed into anhydrous hydrocyanic acid cooled by ice, 
a crystalline body is formed, -which has the composition HCN.HI. It is readily 
soluble in water and alcohol, but not in ether, and may be sublimed with little decom- 
position. This substance is not acid, and does not answer to the tests for hydrocyanic 
acid. "When decomposed by potash, it gives ammonia, formiate of potash, and iodide 
of potassium, so that it may be regarded as the hydriodate of an ammonia formed 
by the substitution of one molecule of the triatomic radical formyle (CH) for the 
three atoms of hydrogen ; or hydriodate of formylo/mine N(CH)'".HI. 

317. Cyanogen itself (C^N") can be prepared by the mere action of heat 
upon the cyanide of mercury (in a test-tube provided with a glass jet for 
burning the gas, fig. 283). This salt resolves itself into metallic mercury 
cyanogen, and a brown substance which has been 
called paracyanogen (C 3 ]N" 3 ), and appears to have » 

been formed by the union of three molecules / 

of cyanogen. Cyanogen gas is easily distin- A *—, 

guished from all others by its peculiar odour and ' I tBl 

its property of burning with a fine peach-coloured •. jj WP 

flame. Being nearly twice as heavy as air (sp. gr. J// Eg 

1 # 8), it may be collected by downward displace- W J8 

ment, for water dissolves about four times its jj^ _-l§L -^ 

volume of the gas, yielding a solution which is j^Jgjjm^ . ._ ■ . : l pliib 
prone to undergo a spontaneous decomposition ^ =^^^m BS^^~ 
remarkable for the comparatively complex pro- Fig. 283. 

ducts which it furnishes, amongst which we trace 

the oxalate (xsH 4 ) 2 C 2 4 and formiate (XH 4 CH0 2 ) of ammonia, and urea 
(CH 4 XO), all derived, be it remembered, from the elements of cyanogen 
and water. In its chemical relations, cyanogen presents a striking resem- 
blance to chlorine. Thus, at a slightly elevated temperature, potassium 
and sodium take fire in it, forming the cyanides of those metals, precisely 
as the chlorides would be formed. Again, when cyanogen is absorbed 
by a solution of potash, the cyanide of potassium and cyanate of potash 
are formed — 

2KHO + Cy a - KCyO + KCy + H 2 0, 

Cyanate of Cyanide of 
potash. potassium. 

just as the chloride of potassium and hypochlorite of potash result from 
the action of chlorine upon potash, 2KHO + Cl 2 = KCIO + KC1 + H 2 0. 
A pressure of about 4 atmospheres is required to liquefy cyanogen, when 
it forms a colourless liquid of sp. gr. 0*87, freezing to a crystalline mass 
at - 30° F. 

Cyanide of potassium. — The most useful of the cyanides is the cyanide 
of potassium, which is extensively employed in electro-plating and gilding, 

This salt may be formed by a very interesting process, which is one of 
the few in which the atmospheric nitrogen takes part, and consists in 
passing air over red-hot charcoal which has been previously soaked in a 
strong solution of carbonate of potash and dried, when the nitrogen requi- 



436 CYANIDE OF POTASSIUM. 

site for the formation of the cyanide is absorbed from the air, and carbonic 
oxide is disengaged — 

K 2 O.C0 2 + C 4 + N 2 = 2KCN (Cyanide of potassium) + 3CO . 

It is probably by a similar Change that the cyanide of potassium is pro- 
duced in the blast-furnaces (page 302) in which iron ores are reduced, 
the potash being derived from the ash of the fuel. The cyanide is always 
prepared for use from the ferrocyanide, which is resolved by a very high 
temperature into cyanide of potassium and carbide of iron, with evolution 
of nitrogen. 

K 4 C y6 Fe<*3S = 4KCy«S£$ + FeC 2 + N, . 

In order to avoid the loss of the two molecules of cyanogen, it is usual 
to fuse the ferrocyanide with carbonate of potash in the proportion of 3 
parts of the dry carbonate to 7 parts of the dried ferrocyanide ; the mixture 
is fused in a covered earthen crucible, and occasionally stirred until gas 
ceases to be evolved ; the crucible is then removed from the fire, allowed 
to stand for a minute or two that the metallic iron may subside, and the 
clear fused, cyanide poured out on to a stone. The change involved in 
this process is represented by the following equation — 

K 4 Cy 6 Fe + K 2 O.C0 2 = 5KCy + KCyO + Fe + C0 2 , 

Cyanate of potash. 

whence it will be seen that the commercial cyanide of potassium is con- 
taminated with cyanate of potash. It also contains a considerable quan- 
tity of carbonate of potash, so that the proportion of cyanide is often only 
60 per cent. The white porcelain-like masses of cyanide of potassium 
deliquesce when exposed to the air, and emit the odour of hydrocyanic acid 
as well as that of ammonia ; the former is disengaged from the cyanide by 
the action of the atmospheric carbonic acid, whilst the ammoniacal odour 
is due to the carbonate of ammonia produced by the action of moisture 
upon the cyanate of potash — 

2KCM) + 4H 2 = K 2 O.C0 2 + (NH 4 ) 2 O.C0. 2 . 

Cyanate of potash. 

Pure cyanide of potassium is deposited in colourless cubical crystals 
when vapour of hydrocyanic acid is passed into an alcoholic solution of 
potash, or it may be obtained by boiling the commercial cyanide with 
alcohol and filtering while hot, when the cyanide crystallises out as the 
solution cools. 

The use of cyanide of potassium in electro-plating and gilding depends 
upon the power of a solution of the salt to dissolve the cyanides of gold 
and silver, forming compounds which are easily decomposed by the gal- 
vanic current, with deposition of metallic gold or silver upon any object 
capable of conducting the current, which may be attached to the negative 
pole (p. 361). Solution of cyanide of potassium is also able to dissolve 
metallic silver and sulphide of silver, which is taken advantage of in 
removing photographic stains from the hands, and in cleaning silver or 
gold lace. 

At a high temperature, cyanide of potassium is a very powerful reducing 
agent, abstracting an atom of oxygen from most of the metallic oxides, 
so as to liberate the metals, being itself converted into cyanate of 
potash. Thus, when the binoxide of tin is fused with cyanide of potas- 



SULPHOCYANIDE OF POTASSIUM. 437 

sium, Sn0 2 + 2KCy = Sn + 2KCyO. This property of the cyanide is 
often applied in chemical experiments. The cyanate of potash is readily 
distinguished by the peculiar pungent odour of cyanic acid, which it emits 
when treated with dilute sulphuric acid, though the greater part of the 
cyanic acid is decomposed with effervescence, yielding sulphate of ammonia 
and carbonic acid — 

2KCTO + 2(H 2 O.S0 3 ) + 2H 2 = K 2 O.S0 3 + (NH 4 ) 2 O.S0 3 + 2C0 2 . 

When fused cyanate of potash is triturated with dried oxalic acid, and 
the mass treated with water, a white insoluble substance is left, which has 
been called cyamelide, and has the composition CHNO, being metameric 
with hydrated cyanic acid, HCNO ; when this substance is distilled, 
hydrated cyanic acid passes over as a colourless liquid, which can only be 
preserved at a very low temperature, for if the receiver containing it be 
removed from the freezing mixture employed to condense the cyanic acid, 
the latter becomes hot and turbid, soon begins to boil violently, and is 
converted into a white mass of cyamelide resembling porce]ain. 

Cyanide of potassium when fused with sulphur, forms a compound cor- 
responding to cyanate of potash, but containing sulphur in place of 
oxygen, and having the formula KCyS, which is commonly spoken of as 
sulphocyanide of potassium, being represented as containing a compound 
radical, sidphocyanogen CyS = Scy. The sulphocyanide of potassium 
is generally prepared by fusing 3 parts of dried ferrocyanide of potas- 
sium and 1 part of carbonate of potash (the materials for making cyanide 
of potassium) with 2 parts of sulphur, in a covered crucible. By washing 
the cooled mass with boiling water, the sulphocyanide is extracted, and 
may be obtained by evaporating the solution, in prismatic crystals 
resembling nitre. By decomposing the sulphocyanide of potassium with 
acetate of lead, the sulphocyanide of lead (Pb(CyS).,) is obtained, and 
this, when acted upon with sulphuretted hydrogen, yields sulphide of 
lead and hydrosidphocyanic acid, HCyS, the latter being a colourless 
oily liquid which may be crystallised by cold. This acid is remarkable 
for the dark red colour (due to sulphocyanide of iron) which it gives with 
the per-salts of iron, for which sulphocyanide of potassium is frequently 
employed as a test. A very delicate test (Liebig T s test) for hydrocyanic 
acid, in cases of poisoning, is also founded upon that circumstance, for if a 
watch-glass moistened with yellow sulphide of ammonium (p. 271) be 
exposed to the action of vapour of hydrocyanic acid, the latter is absorbed 
and converted into sulphocyanide of ammonium — 

(NHJ 8 S + S 2 + 2HCy - 2NH 4 CyS + H 2 S , 

Yellow sulphide Sulphocyanide 

of ammonium. of ammonium. 

by applying a gentle heat to the watch-glass, any excess of sulphide of 
ammonium is volatilised, and a drop of perchloride of iron will then give 
the blood-red colour with the sulphocyanide. 

318. Ferricyanide of potassium.- — When chlorine is passed into a solu- 
tion of ferrocyanide of potassium, the liquid assumes a brown colour, and, 
when evaporated, deposits beautiful red rhombic prisms, which are found, 
on analysis, to have the composition K 3 Cy 6 Fe, having been formed from 
the ferrocyanide according to the equation — 

KfV T?o (ferrocyanide pi _ T ,- n tj (Ferricyanide jT-pi 

4^J6 Xe of potassium) + ^ L - J-V 3 W 6 re of potassium) T lv ^ i » 



438 EED PRUSSIATE OF POTASH. 

This salt is known as red prussiate of potash, or ferricyanide of potas- 
sium, and is used in dyeing ; for if a piece of stuff be heated in a solution 
of the ferricyanide acidulated with acetic acid, a blue compound similar to 
Prussian blue is deposited in the fibre. 

Ferricyanide of potassium is also employed for the preparation of Turn- 
bull's blue (ferricyanide of iron), which is precipitated when a solution of 
that salt is mixed with one of sulphate of iron. 

3(FeO.S0 3 ) + 2K 8 (Cy 6 ¥e) = 3(K 2 O.S0 3 ) + Fe/Cy.Fe), . 

Ferricyanide Ferricyanide 

of potassium. ' of iron. 

In calico-printing, a mixture of the ferricyanide of potassium with potash 
is employed as a discharge for indigo, such a mixture acting as a powerful 
bleaching agent, in consequence of its tendency to impart oxygen to any 
substance in need of that element, the ferricyanide being converted into 
the ferrocyanide ; thus — 

2K 3 (Cy 6 Fe) g£g2? + 2KHO = 2K 4 (Cy^e) <£[££? + + H 2 . 

The ferricyanide of potassium is assumed to contain a compound radical 
ferricyanogen (Cy 6 Fe), which differs from ferrocyanogen in containing 
triatomic iron Fe"', instead of diatomic iron, Fe". The formula Cy/Fe'" 
shows that this radical must be triatomic, and not tetratomic like Cy 6 / Fe // . 
The hydroferricyanic acid (H 3 Cy 6 Fe) can be obtained in a crystallised 
state, and many of the corresponding ferricyanides have been examined. 

Ferrocyanogen and ferricyanogen are not the only compound radicals of 
this description ; there are cobalticyanogen (Cy 6 Co), manganicyanogen 
(Cy 6 Mn), chromicyanogen (Cy 6 Cr), platinocyanogen (Cy 4 Pt), palladio- 
cyanogen (Cy 4 Pd), and iridiocyanogen (Cy 6 Ir), but none of these have 
received any useful applications. The platinocyanides are remarkable for 
their brilliant colours. 

319. Chlorides of cyanogen. — When moist cyanide of mercury is shaken 
up in a bottle of chlorine' gas, and set aside for some time in a dark place, 
the yellow colour of the chlorine disappears, and the bottle is filled with 
a colourless gas having a remarkably pungent and tear-exciting odour; this 
is the gaseous chloride of cyanogen (CyCl) ; HgCy 2 + Cl 4 = HgCl. 2 + 2CyCl. 
If light have access during this experiment, an oily liquid chloride of 
cyanogen, Cy. 2 Cl. 2 , is produced. 

The chloride of cyanogen gas may be liquefied by a pressure of four 
atmospheres, and if the liquid is kept for some days in a sealed tube, it is 
converted into a white mass of solid chloride of cyanogen, Cy 3 Cl 3 . When 
this is acted on by water, it yields cyanuric acid, H 3 Cy 3 3 , according to 
the equation Cy 3 Cl 3 + 3H 2 = 3HC1 + H 3 Cy 3 3 . This acid is very 
interesting on account of its polymeric relation to cyanic acid (HCyO), 
which may be obtained from it by distillation. It is a tribasic acid, and 
forms, like tribasic phosphoric acid (p. 233), three series of salts, having 
the formulas, respectively, M'Cy 3 3 , M/HCy 3 3 , M'H 2 Cy 3 3 . 

The cyanide of phosphorus, PCy 3 , has been sublimed in tabular crystals 
from a mixture of cyanide of silver and terchloride of phosphorus heated 
in a sealed tube to 280° F. for some hours, and afterwards distilled in 
a current of dry carbonic acid. Cyanide of phosphorus inflames at a very 



PREPARATION OF FULMINATE OF MERCURY. 439 

low temperature, and is decomposed by water, yielding cyanic and phos- 
phorous acids. 

320. Nitroprussides. — "When ferrocyanide of potassium is boiled with dilute nitric 
acid, a point is attained at which the solution gives a slate-coloured precipitate with 
a per-salt of iron ; if it be then boiled with an excess of carbonate of soda, filtered, 
and evaporated, it deposits ruby-red prismatic crystals of nitroprusside of sodium 
(Na 4 Cy 10 N 2 O 3 Fe 2 .4AcL.), from which the nitroprussides of other metals may be 
obtained. 

The hydronitroprussic acid (H 4 Cy 10 N 2 O 3 Fe 2 .2Aq,) has also been prepared and 
crystallised. 

The nitroprussides were found by Hadow to be formed from a double mole- 
cule of the ferricyanides by the exchange of two molecules of cyanogen for a 
molecule of nitrons acid (N 2 3 ), and the simultaneous removal of two atoms of the 
metal with which the ferricyanogen was combined. Thus the double molecule of 
ferricyanide of potassium, K 6 .Cy 12 Fe 2 , becomes nitroprusside of potassium, K 4 , 
Cy 10 N 2 O 3 Fe 2 , when boiled with nitric acid, other products being formed at the same 
time by the oxidising action of the nitric acid. 

Based upon this view of its constitution, a more certain and economical process 
for the production of nitroprusside of sodium was devised by Hadow, which consists 
in acting upon the ferricyanide of potassium with nitrite of soda, acetic acid, and 
bichloride of mercury (corrosive sublimate), when the mercury removes two molecules 
of cyanogen, and the chlorine two atoms of potassium, the nitrous acid of the nitrite 
of soda entering into the residue of the ferricyanide, and converting it into nitro- 
prusside of potassium, which, by double decomposition with the acetate of soda, yields 
acetate of potash and nitroprusside of sodium. The cyanide of mercury crystallises 
out first, and the nitroprusside of sodium may be obtained in crystals from the 
evaporated solution. 

The more recent researches of Stadeler have still further simplified the constitution 
of the nitroprussides. By the action of cyanide of potassium upon ferrous sulphate, 
he obtained an orange precipitate composed of KFe 2 "Cy 5 , in which two atoms of 
diatomic iron have replaced four atoms of monatomic potassium in five molecules of 
the cyanide ; 5KCy + 2Fe"S0 4 = 2K 2 S0 4 + KFe 2 "Cy 5 . 

When this precipitate was treated with nitrite of potash, it furnished nitroprusside 
of potassium; K'Fe 2 "Cy.' + KN0 2 = K 2 'Fe"(NO)'Cy 5 + FeO. 

According to this, the hypothetical radical of the nitroprussides would contain 
Cy 5 (NO)'Fe", representing ferricyanogen Cy 6 Fe" in which (NO)' has replaced Cy'. 
The monatomic character of the NO is shown in the nitrite of potash KN0 2 or 
K'(NO)'0". It will be observed that Stadeler's formula for the nitroprussides differs 
from Hadow's only by a single atom of oxygen in Hadow's molecule, thus — 

Double molecule of nitroprusside of potassium (Stadeler), K 4 Fe 2 N 2 O 2 Cy 10 
Nitroprusside of potassium (Hadow), K 4 Fe 2 N 2 O 3 Cy 10 , 

so that whereas Hadow believed in the substitution of nitrous acid (N 2 O s ) for a part 
of the cyanogen, Stadeler finds that it is really NO, the radical of the nitrous acid 
((NO)'(NO)'0") which replaces the cyanogen. 

On the latter view, the diatomic character of the assumed radical Cy 5 '(NO)'Fe" is 
at once explained, for it evidently requires two atoms of potassium to complete the 
saturation of the Cy 5 . 

The nitroprusside of sodium is used as a test for the alkaline sulphides, with a very 
slight trace of which it gives a magnificent purple colour. Thus, an inch or two of 
human hair, fused with carbonate of soda before the blowpipe, will yield sufficient 
sulphide of sodium to strike a purple tint with the nitroprusside. 

321. The fulminates. — The violently explosive compound known as 
fulminate of mercury, which is so largely employed for the manufacture 
of percussion caps, is connected with the series of cyanogen compounds. 

Preparation of fulminate of mercury. — This substance is prepared by 
the action of alcohol upon a solution of mercury in excess of nitric acid j 
and as this action is of a violent character, some care is necessary in order 
to avoid an explosion. On a small scale, the fulminate may be obtained 
without any risk by strictly attending to the following prescription : — 



440 PROPERTIES OF FULMINATE OF MERCURY. 

Weigh out, in a watch-glass, 25 grains of mercury, transfer it to a half-pint 
beaker, add half an ounce (measured) of ordinary concentrated nitric acid (sp. gr. 
1*42), and apply a gentle heat. As soon as the last particle of mercury is dis- 
solved, place the beaker upon the table, away from any flame, and pour into it, 
pretty quickly, at arm's length, 5 measured drachms of alcohol (sp. gr. 0'87). Very 
brisk action will ensue, and the solution will become turbid from the separation of 
crystals of the fulminate, at the same time evolving very dense white clouds, which 
have an agreeable odour, due to the presence of nitrous ether, aldehyde, and other 
products of the action of nitric acid upon alcohol. The heavy character of these 
clouds is caused by the presence of mercury, though in what form has not been 
ascertained ; much nitrous oxide and hydrocyanic acid are evolved at the same time. 
When the action has subsided, the beaker may be filled with water, the fulminate 
allowed to settle, and the acid liquid poured off. The fulminate is then collected 
on a filter, washed with water as long as the washings taste acid, and dried by 
exposure to air. 

The chemical change involved in the preparation of the fulminate is 
complicated by the formation of the secondary products of the action of 
nitric acid upon alcohol, but if these be left out of consideration, a clear 
idea of the reaction may be obtained. 

The fulminate of mercury is found, on analysis, to contain mercury, 
carbon, nitrogen, and oxygen in proportions corresponding to the formula 
HgC 2 N 2 2 ; if the mercury be supposed to exist in the state of oxide, into 
which it would have been converted by the nitric acid, this formula might 
be written HgO.C 2 N" 2 0. The formula for alcohol is C 2 H 6 0, and the 
fulminate of mercury appears to be derivable from alcohol by the exchange 
of H/ for IST/', and the addition of HgO. It has been remarked (p. 140) 
that the action of nitrous acid (N 2 3 ) upon organic substances frequently 
results in the removal of H 3 from the substance in the form of water ; and 
it may be supposed that this acid, resulting from the de-oxidation of the 
nitric acid by one portion of the alcohol, has acted upon another portion 
so as to eliminate the whole of its hydrogen, and to leave, in exchange, 
2 atoms of nitrogen ; thus, C 2 H 6 '+ N 2 3 - C 2 N 2 + 3H 2 0. It is 
evident that the combining value of the two atoms of triatomic nitrogen 
is equal to that of six atoms of hydrogen.* The substance C 2 N 2 0, sup- 
posed to be combined with the oxide of mercury (though never obtained 
in the separate state), has been named fulminic acid. The chemical con- 
stitution of the fulminate will be more advantageously discussed when 
its properties have been considered. 

Properties of fulminate of mercury. — This substance is deposited in 
the above process in fine needle-like crystals, which often have a grey 
colour from the accidental presence of a little metallic mercury. It may 
be purified by boiling it with water, in which it is sparingly soluble, and 
allowing the fulminate to crystallise from the filtered solution. Very 
moderate friction or percussion will cause it to detonate violently, so that 
it must be kept in a corked bottle lest it should be exploded between the 
neck and the stopper. It is usually preserved in a wet state, with about 
one-fifth its weight of water. Its explosion is attended with a bright 
flash, and with grey fumes of metallic mercury. The simplest equation 
to represent the decomposition would be HgC 2 N 2 Q 2 = Hg + 2CO + N 2 ; 
and its violence must be attributed to the sudden evolution of a large 
volume of gas and vapour from a small volume of solid, for the fulminate 
of mercury, being exceedingly heavy (sp. gr. 4*4), occupies a very small 
space when compared with the gaseous products of its decomposition, 

* This view is supported by the circumstance, that fulminate of silver is abundantly 
formed when nitrous acid is passed into an alcoholic solution of nitrate of silver. 



PREPARATION OF FULMINATE OF SILVER. 441 

especially when the latter are expanded by the heat. The evolution of 
heat during the explosion, apparently in contradiction to the rule that 
heat is absorbed in decomposition, must be ascribed to the circumstance 
that the heat evolved by the oxidation of the carbon exceeds that absorbed 
in the decomposition of the fulminate. A temperature of 360° F. explodes 
fulminate of mercury, and the same result is brought about by touching 
it with a glass rod dipped in concentrated sulphuric or nitric acid. The 
electric spark of course explodes it. 

Cap composition. — The explosion of the fulminate of mercury is so 
violent and rapid that it is necessary to moderate it for percussion-caps. 
For this purpose it is mixed with nitrate or chlorate of potash, the 
oxidising property of these salts possibly causing them to be preferred to 
any merely inactive substances, since it would tend to increase the tem- 
perature of the flash by burning the carbonic oxide into carbonic acid, 
and would thus ensure the ignition of the cartridge. For military caps, 
in this country, chlorate of potash is always mixed with the fulminate, 
and powdered glass is sometimes added to increase the sensibility of the 
mixture to explosion by percussion. Sulphide of antimony is some- 
times substituted for powdered glass, apparently for the purpose of 
lengthening the flash by taking advantage of the powerful oxidising 
action of chlorate of potash upon that compound (p. 163). Since the 
composition is very liable to explode under friction, it is made in small 
quantities at a time, and without contact with any hard substance. 
After a little of the composition has been introduced into the cap, it is 
made to adhere and water-proofed by a drop of solution of shell-lac in 
spirit of wine. 

If a thin train of fulminate of mercury he laid upon a plate, and covered, except 
a little at one end, with gunpowder, it will he found on touching the fulminate with 
a hot wire, that its explosion scatters the gunpowder, hut does not inflame it. On 
repeating the experiment with a mixture of 10 grains of the fulminate and 15 grains 
of chlorate of potash, made upon paper with a card, the explosion will he found to 
inflame the gunpowder. 

By sprinkling a thin layer of the fulminate upon a glass plate, and firing it with 
a hot wire, the separated mercury may be made to coat the glass, so as to give it all 
the appearance of a looking-glass. 

Although the effect produced by the explosion of fulminate of mercury 
is very violent in its immediate neighbourhood, it is very slightly felt at 
a distance, and the sudden expansion of the gas will burst fire-arms, 
because it does not allow time for overcoming the inertia of the ball, 
though, if the barrel escape destruction, the projectile effect of the fulmi- 
nate is found inferior to that of powder. 

The fulminate of mercury is generally contaminated with oxalate of 
mercury (HgC 2 4 ), which is one of the secondary products formed during 
its preparation. 

Fulminate of silver is prepared by a process very similar to that for 
fulminate of mercury, but since its explosive properties are far more 
violent, it is not advisable to prepare so large a quantity. 10 grains of 
pure silver are dissolved, at a gentle heat, in 70 minims of ordinary con- 
centrated nitric acid (sp. gr. 1'42) and 50 minims of water. As soon as 
the silver is dissolved, the heat is removed, and 200 minims of alcohol 
(sp. gr. 0*87) are added. If the action does not commence after a short 
time, a very gentle heat may be applied until effervescence begins, when 
the fulminate of silver will be deposited in minute needles, and may be 



442 CHEMICAL CONSTITUTION OF THE FULMINATES. 

further treated as in the case of fulminate of mercury.* When dry, the 
fulminate of silver must be handled with the greatest caution, since it is 
exploded far more easily than the mercury salt; it should be kept in small 
quantities wrapped up separately in paper, and placed in a card-board box. 
Nothing harder than paper should be employed in manipulating it. The 
violence of its explosion renders it useless for percussion caps, but it is 
employed in detonating crackers. Fulminate of silver is sparingly soluble 
in cold water, but dissolves in 36 parts of boiling water. 

If a minute particle of fulminate of silver be placed upon a piece of quartz, and 
gently pressed with the angle of another piece, it will explode with a flash and smart 
report. 

A throw-down detonating cracker may be made by screwing up a particle of the 
fulminate of silver in a piece of thin paper, with some fragments obtained by crush- 
ing a common quartz pebble. 

The explosion of fulminate of silver may be compared with that of the mercury 
salt, by heating equal quantities upon thin copper or platinum foil, when the ful- 
minate of mercury will explode with a slight puff, and will not injure the foil, but 
that of silver will give a loud crack and rend a hole in the metal. 

If a particle of fulminate of silver be placed upon a glass plate and touched with a 
glass rod dipped in oil of vitriol, it will detonate and leave a deposit of silver upon 
the glass. 

"When fulminate of silver is dissolved in warm ammonia, the solution 
deposits, on cooling, crystals of a double fulminate of silver and ammonia, 
Ag(JSTH 4 )C 2 ]S" 2 2 , which is even more violently explosive, and is dangerous 
while still moist. 

On adding chloride of potassium in excess to fulminate of silver, only 
half the silver is removed as chloride, and the double fulminate of silver 
and potassium, AgKC 2 N 2 2 , may be crystallised from the solution. By 
the careful addition of nitric acid, the K may be replaced by H, and the 
acid fulminate of silver, AgHC 2 N 2 2 , obtained, which is easily soluble 
in boiling water, and crystallises out on cooling ; by boiling with oxide of 
silver, it is converted into the neutral fulminate. 

Various other fulminates and double fulminates have been obtained. 
They are all more or less explosive. 

Chemical constitution of the fulminates. — The fact of the existence of 
double fulminates and acid fulminates renders it necessary to write the 
formula of fulminate of silver, for example, Ag 2 C 2 N 2 2 , instead of AgCNO, 
in order to show that half of the silver is capable of being exchanged for 
another metal or for hydrogen. It will be seen that this formula would 
also represent two molecules of cyanate of silver (AgCNO), but the 
properties of this salt are entirely different from those of the fulminate.' 
That a strong connection exists, however, between the fulminates and 
the cyanogen-compounds, is shown by several reactions. Thus, if fulmi- 
nate of mercury be heated with hydrochloric acid, it is dissolved with 
evolution of a powerful odour of hydrocyanic acid, whilst mercuric chloride 
and oxalate, with hydrochlorate of ammonia, remain in the solution. 
Again, if an excess of fulminate of silver be acted on by hydrosulphuric 
acid, cyanic acid may be obtained in solution, and becomes converted into 
hydrosulphocyanic acid, when the hydrosulphuric acid is in excess. 
By decomposing the double fulminate of copper and ammonia 
(Cu(NH 4 ) 2 (C 2 K 2 2 ) 2 ) with hydrosulphuric acid, there are produced, hydro- 

* If the nitric acid and alcohol are not of the exact strength here prescribed, it may be 
somewhat difficult to start the action unless two or three drops of red nitric acid (contain- 
ing nitrous acid) are added. Standard silver (containing copper) may be used for prepar- 
ing the fulminate. 



PRODUCTS FROM COAL. 443 

sulphocyanic acid and urea, the latter having the same composition as 
cyanate of ammonia — 

Cu(NH 4 ) 2 (C 2 N 2 2 ) 2 + 3H 2 S - CuS + 2H 2 + 2HCNS + 2CII 4 N 2 0. 

Hydrosulphocyanic tt^o 
acid. urea ' 

These reactions have induced many chemists to regard the fulminates 
as compounds of the metallic oxides with an acid having the composition 
Cy 4 2 , intermediate in composition between the hypothetical anhydrous 
cyanic acid (Cy 2 0) and the hypothetical anhydrous cyanuric acid (Cy 6 3 ), 
but neither the anhydrous nor the hydrated fulminic acid has yet been 
obtained in a separate form. This view of the constitution of the fulmi- 
nates, however, has the recommendation of simplicity, and enables the 
greater number of their reactions to be easily explained. 

Fulminate of mercury dissolves when boiled with solution of chloride of potassium, 
and the solution, when evaporated, yields crystals of fulminurate or isocyanurate of 
potash, KC 3 N 3 H 2 0g, which has the same percentage composition as acid cyanurate of 
potash, KH 2 Cy 3 3 , but the acid contained in fulminurate of potash forms only one 
series of salts, and is therefore monobasic. The fulminurates are feebly explosive. 
The production of fulminuric acid from the hypothetical fulminic acid may be 
represented by the equation — 

2(H 2 C 2 K 2 2 ) + H 2 = C0 2 + NH 3 + 



PKODUCTS OF THE DESTRUCTIVE DISTILLATION OE COAL. 

322. Much of the extraordinary progress made by chemistry during 
the last half century must be attributed to the introduction and great 
extension of the manufacture of coal-gas. No other branch of manufac- 
ture has brought into notice so many compounds not previously obtained 
from any other source, and, above all, offering, at first sight, so very 
little promise of utility, as to press urgently upon the chemist the necessity 
for submitting them to investigation. 

Although many important additions to chemical knowledge have re- 
sulted from the labours of those who have engaged in devising the best 
methods of obtaining the coal-gas itself in the state best fitted for con- 
sumption, far more benefit has accrued to the science from investigations 
into the nature of the secondary products of the manufacture, the removal 
of which was the object to be attained in the purification of the gas. 

Of the compounds of carbon and hydrogen, very little was known pre- 
viously to the introduction of coal-gas ; and although the liquid hydro- 
carbons composing coal-naphtha were originally obtained from other 
sources, the investigation of their chemical properties has been greatly 
promoted by the facility with which they may be obtained in large quanti- 
ties from that liquid. The most important of these hydrocarbons, benzole 
or benzine, was originally procured from benzoic acid ; but it would have 
been impossible for it to have fulfilled its present useful purposes, but 
for the circumstance that it is obtained in abundance as a secondary 
product in the manufacture of coal-gas ; for, leaving out of consideration 
the various uses to which benzole itself is devoted, it yields the nitro- 
benzole, so much used in perfumery, and from this we obtain aniline, 
from which many of the most beautiful dyes are now prepared. 

The naphthaline found so abundantly in coal-tar possesses a peculiar 
interest, as having formed the subject of the beautiful researches by which 



444 



MANUFACTURE OF COAL-GAS. 



Laurent was led to propose the doctrine of substitution, which has since 
thrown so much light upon the constitution of organic substances. 

We are also especially indebted to coal-tar for our acquaintance with 
the very interesting and rapidly extending class of volatile alkalies, of 
which the above-mentioned aniline is the chief representative, and for 
plienic or carbolic acid, from which are derived the large number of sub- 
stances composing the phenyle- series. 

The retorts in which the distillation of coal is effected are made either of 
cast-iron or of stoneware, generally having the form of a flattened cylinder, 
and arranged in sets of three or five, heated by the same coal fire (fig. 284). 
The charge for each retort is about two bushels, and is thrown on to the red- 




Fig. 284. — Manufacture of coal-gas. 



hot floor of the retort, as soon as the coke from the previous distillation has 
been raked out ; the mouth of the retort is then closed with an iron plate 
luted with clay. An iron pipe rises from the upper side of the front of the 
retort projecting from the furnace, and is curved round at the upper 
extremity, which passes into the side of a much wider tube, called the 
hydraulic main, running above the furnaces, at right angles to the retorts, 
and receiving the tubes from all of them. This tube is always kept half 
full of the tar and water which condense from the gas, and below the sur- 
face of this liquid the delivery tubes from the retorts are allowed to dip, 
so that although the gas can bubble freely through the liquid as it issues 
from the retort, none can return through the tube whilst the retort is 
open for the introduction of a fresh charge. 

The aqueous portion of the liquid deposited in the hydraulic main is 
known as the ammoniacal liquor, from its consisting chiefly of a solution 
of various salts of ammonia, the chief of which is the sesquicarbonate ; 
sulphide, cyanide, and sulphocyanide of ammonium are also found in it. 

From the hydraulic main the gas passes into the condenser, which is 



PURIFICATION OF COAL-GAS. 



445 



composed of a series of bent iron tubes kept cool either by the large sur- 
face which they expose to the air, or sometimes by a stream of cold 
water. In these are deposited, in addition to water, any of the volatile 
hydrocarbons and salts of ammonia which may have escaped condensa- 
tion in the hydraulic main. Even in the condenser the removal of the 
ammoniacal salts is not complete, so that it is usually necessary to pass 
the gas through a scrubber or case containing fragments of coke, over which 
a stream of water is allowed to trickle in order to absorb the remaining 
ammoniacal vapours. 

The tar which condenses in the hydraulic main is a very complex 
mixture, of which the following are some of the leading components — 





Boiling Point. 


Formula. 


Sp. Gr. 


Neutral Hydrocarbons. 








Liquid. 








Benzole, 


176° F. 


C 6 H 6 


0-88 


Toluole, . 


230° 


C 7 H 8 


0-87 


Xylole, 


284° 


c sHio 


0-87 


Isocumole,* 


338° 


C 9 H 12 


0-85 


Solid. 








Naphthaline, 


423° 


CioH 8 




Anthracene, 


580° 


^U^IO 




Chrysene, . 




^12^8 




Pyrene, 




C 15Hl2 




Alkaline Products. 








Ammonia, . 




NH 3 




Aniline, 


360° 


C 6 H 7 N 


1-02 


Picoline, 


271° 


C 6 H 7 N 


0-96 


Quinoline, . 


462° 


C 9 H 7 N 


1-08 


Pyridine, . 


240° 


C 5 H 5 N 




Acids. 








Carbolic acid, 


370° 


C 6 H- 6 


1-07 


Kresylic ,, 


397° 


C 7 H 8 




Rosolic ,, 




C 2 3H 22 4 




Brunolic, ,, 








Acetic „ 


243° 


2 H 4 O 2 


1-06 

1 



The gas is now passed through the lime-purifier, which is an iron box 
with shelves, on which dry slaked lime is placed in order to absorb the 
carbonic acid and sulphuretted hydrogen, and the last portions of ammonia 
are removed by passing the gas through dilute sulphuric acid. 

A great many other methods have been devised for the purification of 
the gas from sulphuretted hydrogen, but none appears to be so efficacious 
and economical as that which consists in passing the gas over a mixture 
of sulphate of iron (green vitriol or copperas), slaked lime, and saw-dust 
(which is employed to prevent the other materials from caking together). 

* Benzole, originally derived from benzoic acid ; toluole, from balsam of tolu ; xylole, 
found among the products from wood (%v\ov) ; isocumole, isomeric with cumole, obtained 
from oil of cummin. 



446 



PURIFICATION OF COAL-GAS. 



The lime decomposes the sulphate of iron, forming sulphate of lime and 
hydrated oxide of iron — 



FeO.SO, 



CaO.H 2 



CaO.SO, 



- FeO.H 2 

The action of air upon the mixture soon converts the oxide into sesqui- 
oxide of iron, which absorbs the sulphuretted hydrogen and the hydro- 
cyanic acid, producing with the former sulphide of iron, and with the 
latter Prussian blue, or some similar compound. The sulphate of lime 
existing in this purifying mixture, is useful in absorbing any vapour of 
carbonate of ammonia from the gas, forming sulphate of ammonia and 
carbonate of lime.* 

The action of the sulphuretted hydrogen on the sesquioxide of iron 
may be thus represented, Fe 2 3 + 3H 2 S = 2FeS + S + 3H 2 ; and the cir- 
cumstance which especially conduces to the economy of the process, is the 
facility with which the sulphide of iron may be reconverted into the 
sesquioxide by mere exposure to the action of atmospheric oxygen, for 
2FeS + 3 = Fe 2 3 + S 2 , thus reviving the power of the mixture to absorb 
sulphuretted hydrogen. Accordingly, if a small quantity of air be ad- 
mitted into the purifier together with the gas, it reconverts the sulphide of 
iron into sesquioxide, and the oxidation is attended with enough heat to 
convert into vapour any benzole which may have condensed in the purify- 
ing mixture, and of which the illuminating value would otherwise be lost. 
The same purifying mixture may thus be employed to purify a very large 
quantity of gas, until the separated sulphur has increased its bulk to an 
inconvenient extent, when it is distilled off in iron retorts. The various 
processes which have been devised for the removal of the bisulphide of 
carbon vapour are mentioned at p. 219. 

The purified gas is passed into the gasometers, from which it is sup- 
plied for consumption. 

In the manufacture of coal-gas, attention is requisite to the temperature 
at which the distillation is effected, for if it be too low, the solid and 
liquid hydrocarbons will be formed in too great abundance, not only 
diminishing the volume of the gas, but causing much inconvenience by 
obstructing the pipes. On the other hand, if the retort be too strongly 
heated, the vapours of volatile hydrocarbons, as well as the olefiant gas 
and marsh-gas, may undergo decomposition, depositing their carbon upon 
the sides of the retort, in the form of gas-carbon, and leaving their hydro- 
gen to increase the volume and dilute the illuminating power of the gas. 

These effects are well exemplified in the following analyses of the gas 
collected from Wigan cannel coal at different periods of the distillation : — 



In 100 volumes. 


1st hour. 


5th hour. 


10 th hour. 


Olefiant gas and volatile hydrocarbons, 
Marsh-gas, ...... 

Carbonic oxide, ..... 

Hydrogen, ...... 

Nitrogen, 


13-0 

82-5 
3-2 

o-o 

1-3 


7-0 
56-0 
11-0 
21-3 

47 


o-o 

20-0 
lO'O 
60-0 

io-o 



The increase of the carbonic oxide after the first hour must be attri- 
buted to the decomposition of the aqueous vapour by the carbon as the 
temperature rises, and the increase of the nitrogen may probably be 

* Sesquioxide of iron itself, derived from various natural and artificial sources, is also 
employed for the purification of coal-gas. 



COAL-NAPHTHA. 447 

ascribed to the decomposition of the ammonia into its elements at a high 
temperature. 

323. One of the most useful of the secondary products of the coal-gas 
manufacture, is the ammonia, and this process has been already noticed as 
a principal source of the ammoniacal salts found in commerce. 

Next in the order of usefulness stands the coal-tar, which deserves 
attentive consideration, not only on that account, but because the extrac- 
tion of the various useful substances from this complex mixture affords an 
excellent example of proximate organic analysis, that is, of the separa- 
tion of an organic mixture into its immediate components. 

For the separation of the numerous volatile substances contained in 
coal-tar, advantage is taken of the difference in their boiling points, which 
will be observed on examining the table at p. 445. 

A large quantity of the tar is distilled in an iron retort, when water 
passes over, holding salts of ammonia in solution, and accompanied by a 
brown oily offensive liquid which collects upon the surface of the water. 
This is a mixture of the hydrocarbons which are lighter than water, viz., 
benzole, toluole, xylole, and isocumole, all having, as represented in the 
table at p. 445, a specific gravity of about 0*85. 100 parts of the tar 
yield, at most, 10 parts of this light oil. 

As the distillation proceeds, and the temperature rises, a yellow oil 
distils over, which is heavier than water, and sinks in the receiver. This 
oil, commonly called dead oil, is much more abundant than the light oil, 
amounting to about one-fourth of the weight of the tar, and contains those 
constituents of the tar which have a high specific gravity and boiling 
point, particularly naphthaline, aniline, quinoline, and carbolic acid. The 
proportion of naphthaline in this oil augments with the progress of the 
distillation, as would be expected from its high boiling point, so that the 
last portions of the oil which distil over become nearly solid on cooling. 
When this is the case, the distillation is generally stopped, and a black 
viscous residue is found in the retort, which constitutes pitch, and is 
employed for the preparation of Brunswick black and of asphalt for 
paving. 

The light oil which first passed over is rectified-by a second distillation, 
and is then sent into commerce under the name of coal naphtha, a quan- 
tity of the heavy oil being left in the retort, the lighter oils having lower 
boiling points. 

This coal naphtha may be further purified by shaking it with sulphuric 
acid, which removes several of the impurities, whilst the pure naphtha 
collects on the surface when the mixture is allowed to stand. When this 
is again distilled it yields the rectified coal naphtha. 

This light oil, especially when distilled from caimel coal at a low temperature, 
contains, in addition to the hydrocarbons above enumerated, some belonging to the 
marsh-gas series (CnH-2 n + 2), and others more recently brought to light, belonging to a 
series the general formula of which is CnH 2 n— 2 ; but these last appear to be acted on 
by the sulphuric acid, employed to remove the basic substances from the light oil, in 
such a manner that they are converted into polymeric hydrocarbons, having the gene- 
~f 4n _4, of which the three following have been particularly examined: — 



Formula. 



C 14 H 24 
Ci 6 H 2 8 
The hydrocarbons, C 6 H 10 , C 7 H 12 , and C 8 H U , from which these appear to have been 



Boiling point. 
410° F. 
464° 
536° 



448 



SEPARATION OF THE HYDROCARBONS IN COAL-NAPHTHA. 



formed by the action of sulphuric acid, would evidently be the higher homologues 
of acetylene, C^Hg. 

The distillation of cannel coal, and of various minerals nearly allied to coal, at low 
temperatures, is now extensively carried on for the manufacture of paraffine and 
paraffine oil. (See Paraffine.) 

The separation of the hydrocarbons composing this naphtha is effected 
by a process in constant use for similar purposes, and known as fractional 
distillation. 

This consists in distilling the liquid in a retort (A, fig. 285) through 
the tubulure of which a thermometer (T) passes, to indicate the tempera- 
ture at which it boils. The first portion which distils over will, of course, 




Fis;. 285. — Fractional distillation. 



consist chiefly of that liquid which has the lowest boiling point ; and if 
the receiver (E) be changed at stated intervals corresponding to a certain 
rise in the temperature, a series of liquids will be obtained, containing 
substances the boiling points of which lie within the limits of temperature 
between which such liquids were collected. 

When these liquids are again distilled separately in the same way, a 
great part of each is generally found to distil over within a few degrees 
on either side of some particular temperature, which represents the boil- 
ing point of the substance of which that liquid chiefly consists ; and if the 
receivers be again changed at stated intervals, a second series of distillates 
will be obtained, the boiling points of which are comprised within a 
narrower range of temperature. It will be evident that, by repeated dis- 
tillations of this description, the mixture will eventually be resolved into 
a number of liquids, each distilling over entirely at or about one par- 
ticular degree, viz., the boiling point of its chief constituent. 

To apply this to the separation of the constituents of light coal naphtha. 

The crude light oil is first agitated with dilute sulphuric acid, which removes any 
basic substances present in it, and afterwards with a dilute solution of potash, to 
separate carbolic acid. The adhering potash is removed by shaking with water, and 
the naphtha is allowed to remain at rest, so that all the water may settle down, and 
the naphtha may be drawn off for distillation. 

The naphtha begins to boil at about 160° F., but a small quantity distils over 
before the temperature has risen to 180°, when the receiver may be changed ; between 
180° and 200° a considerable quantity of the naphtha distils over, and .at the latter 
degree the receiver is changed a second time. The receiver is changed at every 20° 






FRACTIONAL DISTILLATION. 



449 



throughout the distillation, until nearly the whole of the naphtha has passed 
over, which will he the case at about 360°.* 

Ten unequal quantities of liquid will have been thus obtained, diminishing as the 
temperature rises. 

Each of these must then be distilled in a smaller retort than the first, also pro- 
vided with a thermometer. 

The first portion (160° to 180°) will probably begin to boil at 150°, and will distil 
in great part before 160°, when the receiver may be changed. When the tempera- 
ture reaches 170° it will probably be found that nothing remains worth distilling. 
The liquid passing over in this distillation between 160° and 170° may be added to 
that which is next to be distilled (180° to 200°). 

The second portion (180° to 200°) will begin to boil at about 175°, and will distil 
over chiefly between that temperature and 185°, when the receiver may be changed. 
Nearly the whole will have passed over before 1 95°, and this last fraction may be 
added to that previously obtained from 200° to 220°. 

When all the first series of liquids have been thus distilled, it will be found that 
the second series consists chiefly of six portions distilling between the following 
degrees of temperature, viz., 150°-160°, 175°-185°, 180°-190°, 240°-250°, 300°-310°, 
340°-350°. 

By another distillation of each of these portions, a third series of liquids will be 
formed, consisting chiefly of five portions distilling between the following points, viz., 
145°-150°, 175°-180°, 230°-235°, 288°-293°, 336°-342°. 

The portion distilling between 145° and 150° is comparatively small in quantity, 
and has not yet been fully examined. 

That obtained between 175° and 180° is more abundant than either of the others, 
and is nearly pure benzole (C 6 H 6 ). 

The portion boiling between 230° and 235° is chiefly toluole (C 7 H 8 ), whilst 288° to 
293° gives xylole (C 8 H 10 ), and 366° to 342° isocumole (C 9 H 12 ). 

In order to separate the benzole completely from the hydrocarbons which still 
adhere to it, the portion boiling between 175° and 180° is exposed to a temperature 
of 32°, when the benzole alone freezes, the other hydrocarbons remaining liquid, and 
being easily extracted by pressure. 

A simpler method of separating liquids which have different boiling points con- 
sists in distilling them in a flask (F, fig. 286) connected with a spiral worm (W) of 




Fractional distillation. 



pewter or copper, surrounded by water, or some other liquid, maintained at a tem- 
perature just above the boiling point of the particular liquid which is required to 
distil over. The greater part of the less volatile liquids will condense in the worm 
and run back into the flask. Thus, in extracting benzole from the light oil, the liquid 
in A might be kept at 180° F., when the toluole, &c, would be partly condensed m 

* On the large scale, that portion of the naphtha which is distilled over between 180° and 
250° F. is sold as benzole, and employed for the preparation of aniline. 

2 F 



450 ANILINE OR PHENYLAMINE. 

the worm, and the portion which passed into the receiver would consist chiefly of 
benzole. When little more distilled over, the temperature of A might be raised to 
230° and the receiver changed, when the distillate would contain toluole as its pre- 
dominant constituent, and so on . 

324. Benzole. — The pure benzole is a brilliant colourless liquid, exhal- 
ing a powerful odour of coal-gas; it boils at 176° F., and is very inflam- 
mable, burning with a smoky flame. It mixes readily with alcohol and 
wood-spirit, but not with water. Its property of dissolving caoutchouc 
and gutta percha renders it very useful in the arts, and it is an excellent 
solvent for the removal of grease, paint, &c., from clothes and furniture. 

Benzole combines directly with chlorine to form a solid chloride of benzole, C 6 H 6 C1 6 , 
which is decomposed by an alcoholic solution of potash, yielding chlorobenzole, 
C 6 H 3 C1 3 . 

By the action of an aqueous solution of hypochlorous acid upon benzole, a crys- 
talline body has been obtained, having the composition C 6 H 9 C1 3 3 , and called tri- 
chlorhydrine of phenose. When acted on by alkalies, this substance yields a sweet 
substance called phenose, isomeric with dry grape-sugar — 

C 6 H 9 C1 3 3 + 3KHO = C 6 H 12 6 {Phenose) + 3KC1 . 

This substance has not been crystallised ; it forms a deliquescent amorphous 
mass, which is easily soluble in water and alcohol, but insoluble in ether. It reduces 
the oxides of copper and silver like grape-sugar, and when acted on by nitric acid 
is converted into oxalic acid. Phenose has not been found capable of fermentation 
by yeast. 

325. Aniline. — The chief purpose to which benzole is devoted is the 
preparation of aniline, which is subsequently converted into the brilliant 
dyes now so extensively used. It has been already noticed at p. 134, 
that when benzole is dissolved in fuming nitric acid, violent action takes 
place, and a dark red liquid is formed, from which water precipitates a 
heavy yellow oily liquid, smelling of bitter almonds, and known as nitro- 
benzole, which has the composition C 6 H 5 (N0 2 ), and may be regarded as 
derived from benzole by the substitution of a molecule of nitric peroxide 
for an atom of hydrogen — 

C 6 H 6 {Benzole) + HM) 3 = C 6 IL(N0 2 ) {Nitrobenzole) + H 2 . 

When nitrobenzole is placed in contact with diluted sulphuric acid and 
metallic zinc, the (nascent) hydrogen removes the whole of the oxygen, 
and two atoms of hydrogen are acquired instead, producing C 6 H 5 NH 2 , 
or CgHylS", aniline — 

C 6 H 5 (N0 2 ) {Nitrobenzole) + H 6 = C 6 H 7 N {Aniline) + 2H 2 . 

That aniline has been produced may be shown by neutralising the 
excess of sulphuric acid with potash, and adding chloride of lime (hypo- 
chlorite of lime), which gives a fine purple colour with aniline. 

The conversion of nitrobenzole into aniline on a large scale is more 
conveniently effected by gently heating it, in a retort, with water, iron 
filings, and acetic acid, when the deoxidising action of the acetate of 
iron Fe(C 2 H 3 2 ) 2 , first produced, materially assists the change, this 
salt being converted into a basic peracetate of iron 2[Fe 2 (C 2 H 3 2 )JFe 2 3 , 
which is left in the retort, and the aniline may be distilled over, 
accompanied by water. At the close of the distillation a red oil 
passes over, which solidifies to a crystalline mass. This is azobenzide, 
C 6 H 5 N, originally obtained by distilling nitrobenzole with an alcoholic 
solution of potash. 



DYES FROM COAL-TAR. 451 

(When nitrobenzole, in alcoholic solution, is reduced by zinc in the 
presence of hydrochloric acid, the solution neutralised by carbonate of soda 
and boiled with alcohol, a crystalline compound of aniline with chloride 
of zinc (ZnCl 2 .2C 6 H 7 N) is obtained.) 

Since aniline is only slightly soluble in water, and has the sp. gr. 1 *02, 
the larger portion of it collects at the bottom of the liquid in the receiver, 
which is milky from the presence of minute drops of aniline in suspension. 
By pouring the contents of the receiver into a tall vessel, the greater part 
of the aqueous fluid may be separated, and the aniline may be purified by 
a second distillation, when the remaining water will pass over first, the 
boiling point of aniline being 360° F. 

Aniline * presents many striking features ; though colourless when per- 
fectly pure, it soon becomes brown if exposed to the air ; its odour is 
very peculiar and somewhat ammoniacal, and its taste is very acrid. A 
drop falling upon a deal table stains it intensely yellow. But the charac- 
ter by which aniline is most easily recognised, and that which leads to 
its useful applications, is the production of a violet colour with solution 
of chloride of lime, by which a very minute quantity of aniline may be 
detected. The exact nature of the chemical change connected with the 
production of this colour has not been determined, but it is known to be 
an oxidation, and a great number of processes have been patented from 
time to time for the production of crimson, purple, and violet dyes by 
the action of various oxidising agents upon aniline. 

326. Coal-tar dyes. — The first dye ever manufactured from aniline on a large scale 
was that known as mauve, f or aniline purple, which is obtained by dissolving aniline 
in diluted sulphuric acid, and adding solution of bichromate of potash, when the 
liquid gradually becomes dark-coloured, and deposits a black precipitate, which is 
filtered off, washed, boiled with coal-naphtha to extract a brown substance, and after- 
wards treated with hot alcohol, which dissolves the mauve. The chemical change 
by which the aniline has been converted into this colouring-matter cannot at present 
be clearly traced, but the basis of the colour has been found to be a substance which 
has the composition C 27 H 24 lSr 4 , and has been termed mauveine. It forms black 
shining crystals, resembling specular iron ore, which dissolve in alcohol, forming a 
violet solution, and in acids, with production of the purple colour. Mauveine com- 
bines with the acids to form salts ; its alcoholic solution even absorbs carbonic acid 
gas. The hydrochlorate of mauveine, C 27 H 24 N 4 ,2HC1, forms prismatic needles with 
a green metallic lustre. 

Very brilliant red dyes are obtained from commercial aniline by the action of 
bichloride (tetrachloride) of carbon, bichloride of tin, perchloride of iron, chloride 
of copper, mercuric nitrate, corrosive sublimate, and hydrated arsenic acid. It will 
be noticed that all these agents are capable of undergoing reduction to a lower state 
of oxidation or chlorination, indicating that the chemical change concerned in the 
transformation of aniline into aniline red is one in which the aniline is acted on by 
oxygen or chlorine. 

The easiest method of illustrating the production of aniline-red, on the small 
scale, consists in heating a few drops of aniline in a test-tube with a fragment of 
corrosive sublimate (perchloride of mercury), which soon fuses and acts upon the 
aniline to form an intensely red mass composed of aniline-red, calomel, and various 
secondary products. By heating this mixture with alcohol the red dye is dissolved, 
and a skein of silk or wool dipped into the liquid becomes dyed of a fine red, which 
is not removed by washing. 

On the large scale, Magenta (as aniline-red is commonly termed) is generally pre- 
pared by heating aniline to about 320° F. with hydrated arsenic acid, when a dark 
semisolid mass is obtained, which becomes hard and brittle on cooling, and exhibits 
a green metallic reflection. This mass contains, in addition to aniline red, several 
secondary products of the action, and arsenious acid. On boiling it with water, a 

* Aniline derives its name from anil, the Portuguese for indigo, from which it may he 
obtained by distillation with potash. 

t French for marsh-mallow, in allusion to the colour of the flower, 



452 ROSANILINE— CHRYSANILINE. 

splendid red solution is obtained, and a dark resinous or pitchy mass is left. If 
common salt be added to the red solution as long as it is dissolved, the bulk of the 
colouring matter is precipitated as a resinous mass, which may be purified from cer- 
tain adhering matters by drying and boiling with coal naphtha. The red colouring 
matter is a combination of arsenic acid with a colourless organic base, which has been 
called rosaniline, and has the composition C 20 H 19 N 3 .H 2 O. If the red solution of 
arseniate of rosaniline be decomposed with hydrate of lime suspended in water, a 
pinkish precipitate is obtained, which consists of rosaniline mixed with arseniate of 
lime, and the solution entirely loses its red colour. 

By treating the precipitate with a small quantity of acetic acid, the rosaniline is 
converted into acetate of rosaniline (C 20 H 19 N 3 ,C 2 H 4 O 2 ), forming a red solution, which 
may be filtered off from the undissolved arseniate of lime. On evaporating the 
solution to a small bulk, and allowing it to stand, the acetate is obtained in crystals 
which exhibit the peculiar green metallic lustre of the wing of the rose-beetle, 
characteristic of the salts of rosaniline. This salt is the commonest commercial form 
of Magenta ; its colouring power is extraordinary, a very minute particle imparting 
a red tint to a large volume of water. Silk and wool easily extract the whole of the 
colouring matter from the aqueous solution, becoming dyed a fast and brilliant crim- 
son ; cotton and linen, however, have not so strong an attraction for it, so that if a 
pattern be worked in silk upon a piece of cambric, which is then immersed in a 
solution of Magenta and afterwards washed in hot water, the colour will be washed 
out of the cambric, but the red silk pattern will be left. 

If a boiling solution of the acetate of rosaniline be mixed with excess of ammonia, 
the bulk of the rosaniline will be precipitated, but if the solution be filtered while 
hot, it deposits colourless needles of rosaniline, which become red when expossd to 
the air, from absorption of carbonic acid, and formation of the red carbonate of 
rosaniline. 

Water dissolves but little rosaniline ; alcohol dissolves it abundantly, forming a 
deep red solution. Rosaniline forms two classes of salts with acids, those with one 
molecule of acid (monacid salts) being crimson, and those with three molecules 
{triacid salts) having a brown colour. Thus, if colourless rosaniline be dissolved in 
a little dilute hydrochloric acid, a red solution is obtained, which ' contains the 
monacid hydrochlorate of rosaniline, C 20 N 19 H 3 .HC1 ; but if an excess of hydro- 
chloric acid be added, the red colour disappears, and a brown solution is obtained, 
from which the triacid hydrochlorate, C 20 H 19 N 3 .3HC1, maybe crystallised in brown- 
red needles. 

For experimental illustration of the properties of rosaniline, the liquid obtained by 
boiling a solution of the acetate with a slight excess of lime diffused in water, and 
filtering while hot, is very well adapted. This solution has a yellow colour, and may be 
preserved in a stoppered bottle without alteration. If air be breathed into it through 
a tube, the liquid becomes red from production of carbonate of rosaniline. Characters 
painted on paper with a brush dipped in the solution are invisible at first, but 
gradually acquire a beautiful rose colour. 

When the red solution of hydrochlorate of rosaniline is slightly acidified with 
hydrochloric acid and placed in contact with zinc, the solution becomes colourless, 
the rosaniline acquiring two atoms of hydrogen, and becoming leucaniline (from 
kwxot, white) C 20 H 21 N 3 , the hydrochlorate of which (C 20 H 21 N 3 .3HC1) forms a 
colourless solution. Oxidising agents reconvert the leucaniline into rosaniline. It 
has been observed that^re aniline does not yield aniline-red when heated with cor- 
rosive sublimate or arsenic acid, it being necessary that it should contain another 
organic base, toluidine (C 7 H 9 N), which is derived from toluole (C 7 H 8 ) in the same 
way in which aniline is derived from benzole. Since the benzole obtained from 
coal naphtha almost invariably contains toluole, the aniline obtained from it is very 
seldom free from toluidine. What share the toluidine has in the production of the 
red colour is not understood, but if the aniline be prepared with benzole derived 
from benzoic acid, and therefore free from toluole, no red is obtained. A mixture of 
70 parts of toluidine with 30 of aniline, is said to answer best for the preparation of 
the red and violet-colouring matters. Such a mixture would contain two molecules 
of toluidine (C 7 H 9 N) and one of aniline (C 6 H 7 N), or C 20 H 25 N 3 , only requiring the 
removal of H 6 by an oxidising agent to yield rosaniline C 20 H 19 N 3 . 

Aniline-yellow or chrysanilim (from %ev<rto$, golden) is found among the secondary 
products obtained in the preparation of aniline-red. It forms a bright yellow 
powder resembling chrome-yellow, and having the composition C 20 H l7 N 3 . It is 
nearly insoluble in water, but dissolves in alcohol. Chrysaniline has basic properties 
and dissolves in acids, forming salts. On dissolving it in diluted hydrochloric acid, 
and mixing the solution with the concentrated acid, a scarlet crystalline precipitate 



ANILINE-BLUE — HYDROCYAN-ROSANILINE. 453 

of hydrochlorate of chrysaniline (C 20 H l7 N 3 .2HCT) is obtained, which is insoluble in 
strong hydrochloric acid, but very soluble in water. A characteristic feature of 
chrysaniline is the sparing solubility of its nitrate. Even from a dilute solution of the 
hydrochlorate, nitric acid precipitates the nitrate of chrysaniline (C 20 H l7 N 3 .HNO 3 ; 
in ruby-red needles. 

Aniline-blue is produced when a salt of rosaniline (the commercial acetate, for 
example) is boiled with an excess of aniline, which converts the rosaniline (C 20 H 19 N 3 ) 
into triphenylic rosaniline (C 20 H 26 (C 6 H 5 ) 3 N 3 ), which may be regarded as having been 
formed by the introduction of three molecules of the hypothetical radical phenyle 
(C 6 H 5 ) in place of three atoms of hydrogen, the latter having been evolved in the 
form of ammonia — 

C 20 H 19 N 3 .HC1 + 3[(C 6 H 5 )H 2 N] = C 20 H 16 (C l2 H 5 ) 3 tf 3 .HCl + 3NH . 

Hydrochlorate of Aniline. Hydrochlorate of 

rosaniline. triphenylic rosaniline. 

The hydrochlorate is an ordinary commercial form of aniline-blue ; it has a brown 
colour, refuses to dissolve in water, but yields a fine blue solution in alcohol. If it 
be dissolved in an alcoholic solution of ammonia, the addition of water causes a white 
precipitate of the hydrated base, triphenylic rosaniline, C 20 H 16 (C 6 H.) 3 N 3 .H 2 O, which 
becomes bluish when washed and dried. 

Just as rosaniline yields leucaniline when acted on with, nascent hydrogen, so tri- 
phenylic rosaniline yields triphenylic leucaniline (C 20 H 18 (C 6 H 5 ) 3 lSr 3 ) ; this is not basic 
like leucaniline, but a colourless neutral substance, which is reconverted into blue by 
oxidising agents. Compounds corresponding to triphenylic rosaniline, but containing 
methyle, ethyle, or amyle in place of phenyle, are obtained by digesting rosaniline 
with the iodides of these radicals, at a high temperature, in sealed tubes. Thus, by 
the action of iodide of ethyle (C 2 H S I) upon rosaniline, a blue crystalline body, in- 
soluble in water, but soluble in alcohol, is obtained, which is a compound of ethyle 
iodide with triethylic rosaniline ; C 20 H 16 (C 2 H S ) 3 N 3 . 

C 20 H 19 N 3 + 4C 2 H 5 I = C 20 H 16 (C 2 H 5 ) 3 N 3 .C 2 H 5 I + 3HI . 
Rosaniline. Ethyl-iodate of 

tii-ethyl-rosaniline. 

Aniline- violet appears to be formed in a similar manner. Other compounds have 
been obtained from aniline, presenting almost every variety of colour. A green dye 
is prepared by the action of a mixture of hydrochloric acid and chlorate of potash upon 
aniline, and under particular conditions a black may be obtained with the same agents. 
Another green has been made by acting upon Magenta with aldehyde. 

When a solution of acetate of rosaniline is treated with cyanide of potassium, it 
gradually loses its red colour, and deposits a white crystalline precipitate of a base 
which has been termed hydrocyan-rosaniline, having the formula C 21 H 20 N 4 , and con- 
tains the elements of rosaniline and hydrocyanic acid; but this acid cannot be 
detected in it by the ordinary tests, leading to the belief that the new base should 
be regarded as leucaniline (C 20 H 21 N 3 ), in which one atom of hydrogen is replaced 
by a molecule of cyanogen ((J 2 oH 20 (CN~)N 3 ). The hydrocyan-rosaniline is almost 
insoluble in water, and sparingly soluble in boiling alcohol. When precipitated from 
its salts by adding an alkali, it becomes pink on exposure to sunshine. 

The present extensive application of aniline to the manufacture of these 
dyes affords a most striking example of the direct utility of pure chemistry 
to the arts ; for only twelve or fifteen years ago, the name of this substance 
was not known to any but scientific chemists, whilst at present many 
tons are annually consumed to supply the wants of the dyers of silk and 
woollen goods. 

327. Aniline ranks as a powerful organic base, combining readily with 
acids to form salts which are, generally speaking, easily crystallised. Like 
ammonia, it unites directly with the hydrated acids, without any separation 
of water; thus, the formula of sulphate of aniline is 2C 6 H 7 N.H 2 O.S0 3 , 
just as that of sulphate of ammonia is 2NH 3 .H 2 O.S0 3 . With the 
hydrogen acids, also, aniline unites like ammonia, for hydrochlorate of 
aniline is C 6 H 7 !N".HC1, and hydrochlorate of ammonia, EH 3 .HC1 ; and 
exactly as the addition of potash to the salts of ammonia causes the sepa- 



454 HOMOLOGUES OF BENZOLE. 

ration of ammoniacal gas, so when added to the salts of aniline, it preci- 
pitates that base in the form of oily drops, which render the liquid 
milky. This resemblance in disposition between aniline and ammonia 
leads to the impression that they must be moulded after a common type, 
and, accordingly, aniline is often represented as formed from ammonia 
(NH 3 ) by the substitution of the compound radical phenyle (C 6 H 5 ) for an 
atom of hydrogen, and, upon this supposition, is termed phenylamine, 
NH.fCA) = C ( H,N. 

This view of the constitution of aniline is supported by the circum- 
stance of its formation when phenic or carbolic acid is heated with 
ammonia in a tube hermetically sealed ; for there is reason to believe that 
this acid, mentioned above as one of the chief acid products of the 
destructive distillation of coal, is phenylic hydrate (C 6 H 5 )HO, and its 
action upon ammonia would then be clearly explained by the equation — 

(C 6 H a )HO + NH 3 = 11,0 + NH 2 (C 6 H 5 ) 

«"*• * «S, 

When aniline is dissolved in alcohol and acted on by nitrous acid, two molecules 
of it loses three atoms of (monatomic) hydrogen, and acquire, in their stead, one 
atom of (triatomic) nitrogen, depositing a yellow compound, which has been called 

diazoamidobenzole — 

4C 6 H 7 N + N 2 3 = 2C 12 H n N 8 + 3H 2 . 

Aniline. Diazoamidobenzole. 

When the nitrous acid acts upon a hot solution, a base is formed isomeric with the 
above, and called amido-diphenylimide, which is identical with a yellow colouring 
matter obtained by the action of stannate of soda upon a salt of aniline. Its 
slightly acid solutions impart an intensely yellow colour to silk or wool, which is 
removed by heat, the base being volatile. The action of nitrous acid on aniline 
affords an example of a general method of producing compounds in which nitrogen 
is substituted for hydrogen. 

Accompanying the aniline in coal tar, there are found three other 
bases, viz., pyridine, picoline, and quinoline. It will be seen that pico- 
line (C 6 H 7 N) is isomeric with aniline, from which, however, it differs 
in a very striking manner, for its salts are by no means easily crystal- 
lisable, and it furnishes no violet colour with oxidising agents, such as 
chloride of lime. Picoline occurs among the products of the distilla- 
tion of bones. Quinoline is also formed when some of the vegetable 
alkaloids are distilled with hydrate of potash. 

328. The other constituents of the light coal naphtha, viz., toluole, 
xylole, and isocumole, though not so important as benzole, on account of 
their practical applications, stand in a highly interesting relation to it and 
to each other. 

These four liquids are members of a homologous series, that is, of a series 
the members of which differ by the same number of atoms of the same 
elements. Thus, toluole (C 7 H 8 ) is seen to contain CH., more than ben- 
zole (C 6 H 6 ), just as isocumole (C 9 H 12 ) contains CH 2 more than xylole 
(C 8 H 10 ). On reference to the table at p. 445, it will be seen that the 
boiling points of the members of this series are raised 54° E. for each 
addition of CH. 2 . Thus, xylole (C 8 H 10 ) boils at 284°, or 54° higher than 
toluole (C 7 H g ), which boils at 230°, whilst benzole (C H H 6 ) boils at 54° 
below this, or 176°. 



PHENOLE OE CARBOLIC ACID. 455 

The members of this group are also intimately connected with those 
of another homologous series, known as aromatic acids, including — 



Benzoic acid, . 


• C 7 H 6 2 


Toluic acid, 


• C 8 H 8 2 


Cuminic acid, . 


• C 10 H 12 O 2 



By distilling each of these acids with hydrate of baryta, the correspond- 
ing hydrocarbon is obtained, a molecule of carbonic acid being removed 
by the baryta ; thus, 

C 7 H 6 0. 2 (Benzoic acid) - CO g = C 6 H S (Benzole). 

The similarity between this decomposition and that by which marsh- 
gas (CH 4 ) is derived from acetic acid (C 2 H 4 2 ) will be at once apparent 
(see p. 95). 

Each member of this series of hydrocarbons, "when acted upon by nitric 
acid, yields a nitro-compound corresponding in composition to nitro- 
benzole, and this, under the influence of reducing agents (such as acetate 
of iron, or the hydrosulphate of an alkaline sulphide) yields a base homo- 
logous with aniline. 

Thus we have the three following homolooous series : — 



Hydrocarbon. 


N itro- compound. 


Base. 


Benzole, C 6 H 6 


Nitrobenzole, C 6 H 5 N0 2 


Aniline, C 6 H 7 N" 


Toluole, C 7 H 8 


Nitrotoluole, C 7 H 7 N0 2 


Toluidine, C 7 H 9 N 


Xylole, C 8 H 10 


Nitroxylole, C 8 *H 9 NO a 


Xylidine, C 8 H U N 



329. Carbolic or plienic acid., or phenole (C 6 H 6 0. 2 ), derives its interest 
chiefly from its constituting a great part of the ordinary commercial 
kreasote (from Kpeas, flesh, and o-w^co, to preserve). It is also present in 
cow's urine, and in that of some other animals. It is found chiefly in 
the heavy or dead oil of coal tar (p. 447), particularly in that portion 
which distils over between 300° and 400° F., when the oil is submitted 
to fractional distillation, and it appears to be the carbolic acid which 
confers upon this heavy oil its valuable antiseptic properties, leading to 
its employment for the preservation of wood from decay. 

In order to extract the acid from that portion of the dead oil which distils 
between 300° and 400° F., it is shaken with a hot concentrated solution of hydrate 
of potash and some solid hydrate of potash. A white crystalline mass is deposited, 
which is separated from the liquid portion and treated with a little water, when a 
solution of carbolate of potash is obtained. This is separated from a [quantity of 
oil which floats above it, and decomposed with hydrochloric acid, when the carbolic 
acid separates as an oily layer upon the surface. This is drawn off, digested with 
a little fused chloride of calcium to remove the water, and distilled. The distilled 
liquid, when exposed to a low temperature, solidifies to a mass of long colourless 
needles, which are liquefied even by the warmth of the hand (93° F.). 

Carbolic acid has the peculiar taste and smell of kreasote. It dissolves 
sparingly in water, but readily in alcohol. When a piece of deal is wetted 
with solution of carbolic acid, and afterwards with hydrochloric acid, it 
becomes blue on drying. 

The genuineness of a commercial sample of carbolic acid may be tested by shak- 
ing about a drachm of it with half a pint of warm water, which will dissolve the 
pure acid entirely, but will leave any "dead oil" undissolved. A solution of one 
part of caustic soda in ten parts of water should dissolve five parts of pure carbolic 
acid. 

When carbolic acid is shaken with one-fourth of its weight of water, and exposed 



456 PICRIC OR CARBAZOTIC ACID. 

to a temperature of 39° F., it deposits six-sided prismatic crystals of a hydrate, 
2C 6 H 6 O.H 2 0, which is soluble in water, alcohol, and ether, and fuses at 61° F. 

The acid properties of carbolic acid are of a very feeble and doubtful character. 
It is more properly regarded asphenylic alcohol or phenyle hydrate (C 6 H 5 )HO. 

Carbolic acid is very largely used as an antiseptic agent. In medicine 
it is found very valuable, especially for the treatment of putrid sores ; 
and, in admixture with sulphite of lime, it forms the substance known as 
MacDougalVs disinfectant. 

330. Carbazotic acid. — When carbolic, acid is boiled witb fuming nitric 
acid, the solution, on cooling, deposits beautiful yellow crystals of carba- 
zotic or picric acid, also called trinitropJienic or nitrophenisic acid, be- 
cause it appears to be formed from phenic acid by the substitution of 
3N0 2 for H 3 , just as nitrobenzole is formed from benzole by the substitu- 
tion of N0 2 for H. 

The composition of picric acid, upon this view, would be expressed by 
the formula HC 6 H 2 (N0 2 ) 3 0, the atom of hydrogen being capable of dis- 
placement by a metal, forming a picrate or carbazotate ; thus if the acid be 
added to a solution of potash, a yellow precipitate of carbazotate of potash, 
KC 6 H 2 (N0 2 ) 3 0, is obtained, which has led to the employment of this 
acid as a test for potash. 

Carbazotic acid is not easily soluble in water, but dissolves readily in 
alcohol. Its solutions have the property of staining the skin and other 
organic matters yellow, which is turned to advantage by the silk-dyer. 
The intensely bitter taste of the acid has also led to its employment for 
the adulteration of beer, to simulate the bitter of the hop. 

Carbazotic acid is a very common product of the action of nitric acid 
upon organic substances ; indigo, silk, and many resins furnish it in con- 
siderable quantity. It is economically obtained in a pure state by the 
action of nitric acid upon Botany Bay gum, but considerable quantities 
are manufactured for the dyer by treating the crude carbolic acid from 
coal tar with nitric acid. Carbazotic acid, as might be anticipated from 
its composition, explodes when sharply heated, its carbon and hydrogen 
being oxidised by the nitric peroxide. 

When carbazotic acid is distilled with chloride of lime, it yields a heavy 
colourless oil having a very pungent odour of mustard, and boiling at 
248 u F.* This substance has been called chloropicrine, and has the re- 
markable formula CC1 3 (N0 2 ), which may be represented as formed upon 
the type of marsh-gas, CH 4 , in which three atoms of the hydrogen are 
replaced by chlorine, and the fourth by nitric peroxide. Chloropicrine 
is frequently met with among the products of the action of chlorinating 
agents upon organic substances. It is almost insoluble in water, but 
dissolves easily in alcohol and ether. 

When an alcoholic solution of chloropicrine is acted on by sodium, it 
yields the subcarbonate of ethyle, and when treated with cyanide of potas- 
sium, it exchanges two atoms of chlorine for cyanogen, forming an unstable 
dark red semi-fluid substance, having the composition CClCy 2 (N0 2 ), which 
may be regarded as derived from marsh-gas (CH 4 ) by the substitution of 
two molecules of cyanogen, one atom of chlorine, and one molecule of 
nitric peroxide, for the four atoms of hydrogen. 

It will be instructive to compare the composition of the most important 

* 233° -6 (Hofniaim). 



NAPHTHALINE. 457 

members of the phenyle series, as that group of organic compounds is 
termed, which are derived from the hypothetical radical phenyle (C 6 H 5 ) — 

Benzole or hydride of phenyle, . H(C 6 H 5 ) 

Aniline or phenylamine, . . NH 2 (C 6 H 5 ) 

Phenic acid, .... H(C 6 H 5 )0. 

Trinitrophenic or picric acid, . H[C 6 H 2 (N/0 2 ) 3 ]0 . 

It is evident that whilst aniline may he regarded as ammonia in which 
the hypothetical phenyle is substituted for an atom of hydrogen, phenic 
acid can be represented as formed from a molecule of water by the substi- 
tution of phenyle for half the hydrogen, and benzole may be represented 
as a molecule of hydrogen, HH, in which one of the atoms is replaced 
by phenyle. 

Some specimens of the kreasote found in commerce boil at a higher 
temperature than carbolic acid; this is due to the presence of kresylic 
acid (C 7 H 8 2 ), corresponding to carbolic acid, but regarded as containing 
the hypothetical radical kresyle (C 7 H 7 ) in place of phenyle. The analogy 
in composition is attended with a resemblance in properties, for kresylic 
acid has the same antiseptic property as carbolic acid, and is applicable to 
similar purposes. When acted on by nitric acid, it yields trinitrokresylic 
acid (HC 7 H 4 (JSr0 2 ) 3 0), just as carbolic acid gives trinitrophenic acid 
(HC 6 H 2 (NO s ) s O). 

331. Naphthaline. — The most prominent constituent of the heavy oil 
of coal tar is the naphthaline, which is easily procured in a pure state from 
the portions obtained at the close of the distillation, by simply pressing 
the semisolid mass to remove any liquid hydrocarbons, and boiling with 
alcohol, from which the naphthaline crystallises on cooling in brilliant 
pearly flakes, which may be still further purified by the process of sub- 
limation. 

In itself naphthaline is not very interesting, being a remarkably indif- 
ferent substance,* but it has been made the subject of several beautiful 
investigations which have thrown much light upon the action of chemical 
agents on organic compounds in general. 

The most important of these researches is that upon the action of 
chlorine and bromine on naphthaline, which originated the now almost uni- 
versally accepted doctrine of substitution, and fully established the fact, 
that an element may be replaced in a given compound by an equivalent 
quantity of another element of a totally different chemical character. 

Thus, by the action of chlorine upon naphthaline, the hydrogen is re- 
moved in the form of hydrochloric acid, and there are obtained six new 
compounds by the progressive substitution of chlorine for the hydrogen, 
which Laurent distinguished by names indicating the number of atoms 
of chlorine present by means of the different vowels in the last syllable, 
introducing a new penultimate syllable when the vowels were exhausted, 
as will be seen in the following list : — 



Naphthaline, 


• C 10 H 8 


Chlonaphtuse, 


. Wanting 


Chlonaphtase, 


■ C 10 H 7 C1 


Chlonaphthalase, . 


• C 10 H 2 C1 6 


Chlonaphtese, 


• ^loHeGla 


Chlonaphthalese, . 


. Wanting 


Chlonaphtise, 


• ^ioH 5 Cl 3 


Chlonaphthalise, . 


• C 10 C1 8 . 


Chlonaphtose, 


• c ioH 4 Cl 4 







It will be observed that the original naphthaline type is here preserved 
* A new crimson dye, Magdala, has been prepared from naphthaline. 



458 SUBSTITUTION PRODUCTS FROM NAPHTHALINE. 

throughout, the sum of the atoms being always 18, and the number of 
carbon atoms 10. 

One of the most unexpected results of Laurent's investigation was the 
discovery that some of these compounds may be obtained in several dis- 
tinct forms or modifications, which are isomeric, or have the same compo- 
sition, but exhibit very different properties. Thus, there are seven varieties 
of chlonaphtese, all containing C 10 H 6 C1 2 , and yet differing from each other 
as much as substances not having the same composition. Two of them 
are liquids, and the five solid forms all fuse at different temperatures, 
ranging between 88° and 214° F. Seven different forms of chlonaphtise 
likewise exist, and four of chlonaphtose. 

To account for this, Laurent supposed it to be by no means indifferent 
which particle of hydrogen has been removed from the compound, believing 
each to have its assigned place and specific function. Thus it may easily 
be conceived that the replacement of different particles of hydrogen by 
chlorine should give the seven modifications of chlonaphtese — 

Naphthaline, C 10 HHHHHHHH 

Chlonaphtese a, C 10 C1C1HHHHHH 
Chlonaphtese /?, C 10 HHC1C1HHHH, 

and so on. Other more recent investigations have given greater proba- 
bility to this hypothesis. 

Bromine, as might be anticipated, yields results similar to those with 
chlorine; but it could not have been predicted that substitution com- 
pounds might be obtained in which one part of the hydrogen is replaced 
by chlorine and the other by bromine. Thus, by acting upon a chlorine 
substitution compound with bromine, or vice versa, the following sub- 
stances were produced :* — 

Chlorebronaphtise, C 10 H 5 Cl 2 Br 

Chlorebronaphtose, C 10 H 4 C] 2 Br 2 

Chloribronaphtose, C 10 H 4 Cl 3 Br 

Bromechlonaphtuse, C 10 H 3 Br 2 Cl 3 

Bromachlonaphtose, C 10 H 4 BrCl 3 

It will be observed that chloribronaphtose and bromachlonaphtose have 
the same composition, though they possess different properties, and are 
obtained in very different ways, the former being procured by the action of 
bromine on chlonaphtise (C 10 H 5 C1 3 ), and the latter by the action of chlorine 
upon bronaphtese (C 10 H d Br 2 ). Another confirmation is thus obtained of 
the belief, that upon the position of the hydrogen which is replaced, 
depends the character of the resulting compound. 

Naphthaline is capable of direct union with chlorine to form two 
chlorides of naphthaline, having the formulae C 10 H 8 C1 2 and C 10 H 8 C1 4 , 
which may obviously be regarded as composed of substitution products 
combined with hydrochloric acid. 

When acted upon by nitric acid, naphthaline furnishes three substitu- 
tion products, in which one, two, and three atoms of hydrogen are replacd 
by N0 2 ; and each of these compounds, under the influence of reducing 

* In naming these compounds, Laurent proceeded upon the same principle. The vowel 
immediately alter the syllable chlor- or brom-, indicating the number of atoms of that 
element, whilst the vowel in the last syllable shows how many atoms of hydrogen 
have been replaced. The name begins with chlor- when the compound has been obtained 
by the action of bromine upon a chlorine substitution product, and vice versd. 



PROXIMATE CONSTITUENTS OF WOOD. 459 

agents, yields a base, just as nitrobenzole, under similar treatment, yields 
aniline. 

By prolonging the action of boiling nitric acid upon naphthaline, 
and evaporating the solution, crystals of naphthalic or jphthalic acid, 
H 2 C 8 H 4 4 , are obtained. Through this acid, naphthaline is connected 
with the phenyle series ; for when phthalic acid is heated with lime, it 
is resolved into carbonic acid and benzole — 

H 2 C 8 H 4 4 + 2CaO = C 6 H 6 + 2(CaO.C0 2 ). 

Phthalic acid. Benzole. 

Moreover, by digesting phthalate of lime with hydrate of lime at an 
elevated temperature for several hours, it is converted into benzoate and 
carbonate of lime — 

2CaC 8 H 4 4 + CaO.H 2 - Ca(C 7 H 5 2 ) 2 + 2(CaO.C0 2 ). 

Phthalate of lime. Benzoate of lime. 

Anthracene or Paranaphthaline, C 14 H 10 , which is found among the last 
products of the distillation of coal tar, differs from naphthaline in being 
almost insoluble in alcohol, and fusing only at 356° F., whilst naphthaline 
fuses at 174° F.* 

Chrysene and pyrene are obtained at the close of the distillation of coal 
tar ; they are crystalline solids not possessing any special importance, and 
have also been observed among the products of the destructive distillation 
of fatty and resinous bodies. 



DESTRUCTIVE DISTILLATION OF WOOD. 

332. The destructive distillation of wood may be advantageously 
studied in order to gain an insight into the effects of heat upon organic 
substances comparatively free from nitrogen, just as that of coal may serve 
as a general illustration of the behaviour of nitrogenised bodies under 
similar treatment. 

The principal distinction between the two cases will be found to consist 
in the absence of basic substances from the products of the distillation of 
non-nitrogenised bodies. 

All varieties of wood (freed from sap) consist essentially of cellulose, 
lignine, and mineral substances or ash. The cellulose (C 6 H J0 -O 5 ) com- 
poses the wood-cells, and is therefore the most important constituent of 
the wood, the lignine being the material with which these cells are lined, 
and which appears to have a great influence upon the hardness of woods, 
being more abundant in the harder varieties, and particularly in such 
hard appendages as nut-shells. Lignine is far more easily dissolved by 
alkalies than cellulose, which is scarcely affected by them, but it has not 
hitherto been found possible to isolate the lignine in a state of purity for 
the purpose of determining its exact composition, since it is always accom- 
panied in the wood by resinous matters, giving rise to the differences of 
colour in woods, and by a small quantity of nitrogenised matter, and of 
ash deposited with it from the sap. 

The following results of the analysis of several woods will exhibit their 
general correspondence in composition : — 

* The production of alizarine from anthracene will be noticed hereafter. 



460 



PRODUCTS FROM WOOD. 



Wood 



in vacuo at 284° I*. 





Beech. 


Oak. 


Birch. 


Aspen. 


Willow. 


Carbon, 
Hydrogen, 
Oxygen, . . 
Nitrogen, . . 
Sulphur, . . 
Ash, . . . 


:} 


49-46 

5-96 

42-36 

1-22 

1-00 


49-58 

5-78 

41-38 

1-23 

2-03 


50-29 

6-23 

41-02 

1-43 

1-03 


49-26 

6-18 

41-74 

0-96 

1-86 


49-93 

6-07 

39-38 

0-95 

3-67 


100-00 


100-00 


100-00 


100-00 


100-00 



Cellulose in a nearly pure condition constitutes cotton, linen, and the 
best kinds of (unsized) paper, since the processes to which the woody- 
fibre is subjected in the preparation of these materials, destroy and 
separate the less resistant lignine and the matters which accompany it. 

On comparing the composition of wood with that of coal, it will be 
obvious that the large proportion of oxygen in the former must give rise 
to a great difference in the products of destructive distillation. Accord- 
ingly, it is found that water, carbonic oxide, carbonic acid, and acetic 
acid, all highly oxidised bodies, are produced in large quantity, and that 
the gaseous products of the distillation of wood burn with far less light 
than those from coal, in consequence of the smaller proportion of the 
heavier hydrocarbons. 

The principal products of the action of heat upon wood are — 







Wood Tar. 










Solids. 








Paraffine, . 


C#H2.r + 2 






Pyrene, 




C 15 H 12 


Naphthaline, . 


C10H8 






Chrysene, 




C12H8 


Cedriret, 








Eesin, 






Pittacal, 


















Liquids. 








Toluole, 


C 7 H 8 






Pyroligneous or ) 




CJFLO 


Xylole, 


Cs^io 






acetic acid, ) 






Cymole, 


C 10 H 14 






Wood naphtha, 




CH 4 


Kreasote, 


C 7 H 8 






Acetate of methyl 


3, . 


CH 3 .C 2 H 3 2 


Picamar, 








Formiate of methyle, 


CH 3 .CH0 2 


Kapnomor, . 


c io H iiC- 






Acetone, 


. 


C 3 H 6 


Eupione, 


C 5 H 12 






Water, 










Gases. 








Marsh-gas, 








CH 


4 


Carbonic oxide, 






CO 




Carbonic acid, . 








CO, 





Of these products, by far the most important are the pyroligneous acid, 
the wood naphtha, and acetone. 

The distillation of wood with a view to the preparation of these sub- 
stances, is conducted in the manner described in the section on wood 
charcoal (p. 62), when the distillate separates into two portions, the 
heavier insoluble part constituting the wood tar, whilst the light aqueous 
layer contains the pyroligneous acid, naphtha, and acetone. 

On distilling this, the two last, boiling respectively at 150° and 133° 



METHYLIC ALCOHOL. 461 

F., first distil over, and then the acetic acid, which boils at 243° F. The 
acid so obtained, however, is contaminated with tarry matters, which 
communicate the peculiar odour of wood smoke, and adapt it especially 
for the preservation of meat. In order to obtain pure acetic acid, this 
crude acid is neutralised with carbonate of soda, and the acetate of soda 
thus obtained is moderately heated to expel the foreign substances. It is 
then further purified by solution in water and crystallisation, and is dis- 
tilled with sulphuric acid, which converts the soda into sulphate, leaving 
the acetic acid to distil over. 

333. Wood naphtha — Methylic alcohol. — In order to obtain the wood 
naphtha (or pijroligneous ether, or icood spirit, or pyroxylic spirit), the 
portion which distils over below 212° F. is rectified in a still containing 
chalk, which retains the acetic acid as acetate of lime. 

The wood naphtha so obtained generally consists chiefly of methylic 
alcohol (CH 4 0), but contains also acetone, acetate of methyle, and certain 
oily substances which impart to it a peculiar odour, and cause it to be- 
come milky when mixed with water. "Wood generally yields about one 
part of naphtha to twenty of acetic acid. In order to obtain the pure 
methylic alcohol, chloride of calcium is dissolved to saturation in the 
crude wood spirit, when a definite crystallisable compound is formed, of 
4 molecules of methylic alcohol and 1 of chloride of calcium, CaCl 2 .4CH 4 0. 
This is heated in a retort, placed in a vessel of boiling water, as long as 
any acetone and acetate of methyle pass over, the above compound not 
being decomposed at 212° F. An equal weight of water is then added 
to the residue in the retort, and the distillation continued, when the 
methylic alcohol distils over, accompanied by water, and the chloride of 
calcium remains in the retort. The diluted methylic alcohol is digested 
for some time with powdered quick-lime, and again distilled, when it is 
obtained in a state of purity. 

The useful applications of crude wood naphtha depend upon its burning 
with a nearly smokeless flame in lamps (though as a source of heat only, 
not of light), and upon its power of dissolving most resinous substances 
employed in the preparation of varnishes, stiffening for hats, &c. 

Methylic alcohol is the first member of the very important homologous 
series of alcohols, of which ordinary alcohol or spirit of wine is the type, 
and the consideration of which may be postponed until the chemical 
history of that alcohol shall have been studied. The designation of 
methylic alcohol supposes the existence in the pyroligneous spirit of a 
compound radical methyle* (CH 3 ), of which methylic alcohol is the 
hydrate, (CH 3 )HO. This view is by no means unsupported by experi- 
mental evidence ; for if wood spirit be distilled with four parts of con- 
centrated sulphuric acid, it yields a gas, the composition of which is 
represented by the formula, (CH 3 ) 2 0, and this may be regarded as the 
oxide of methyle. Again, if wood spirit be distilled with iodine and 
phosphorus, the hydriodic acid formed (see p. 179) acts upon the hydrate 
of methyle, producing the compound CH 3 I, iodide of methyle. When 
this is heated in contact with zinc, iodide of zinc is produced, and a gas, 
having the composition CH 3 , which is that of the radical methyle, is 
obtained. (This important question of compound radicals will be more 
fully discussed hereafter.) 

* From fxedv, wine ; DXtj, wood. The termination -yle is generally bestowed upon com- 
pound radicals, because v\t] is put metaphorically for matter. Thus, ethyle is meant to 
imply the matter from which ether compounds are derived. 



462 PARAFFINE. 

A sulphide, bisulphide, chloride, bromide, and cyanide of methyle, may 
also be obtained, as well as compounds of the oxide of methyle with sul- 
phuric, nitric, acetic, &c, acids. The methyle series is, in fact, perfectly 
parallel with the ethyle series, the members of which are far more im- 
portant, and will therefore be more particularly considered hereafter. 

One of the most interesting compounds derived from wood spirit is the 
salicylate of methyle, or oil of winter green (CH 3 .C 7 H 5 3 ), which is ex- 
tracted from the flowers of the Gaultheria procumbens, and was one of 
the first vegetable products to be prepared artificially by the chemist. It 
is obtained by distilling wood spirit with sulphuric acid and salicylic acid 
(HC 7 H 5 3 ), the latter acid being formed by the action of fused hydrate of 
potash upon the salicine (C 13 H 18 7 ) extracted from willow bark. 

It will be noticed that the formiate of methyle, CH 3 .CH0 2 , would have 
the same composition as acetic acid, HC 2 H 3 2 , though they are very dif- 
ferent in constitution. An excellent illustration is here afforded of the 
distinction between an empirical and a rational formula, the former 
simply denoting the composition of a substance, without regard to the 
arrangement of its components, which is always indicated by the rational 
formula. Thus, the empirical formula of acetic acid, as well as of 
formiate of methyle, is C 2 H 4 2 , but the rational formula of the latter is 
CH 3 .CH0 2 , showing it to be derived from formic acid (CH 2 2 ), whilst the 
rational formula of acetic acid is HC 2 H 3 2 . Such compounds are often 
said to be metameric, the term isomeric being usually applied to com- 
pounds having the same composition, but which are not known to possess 
a different constitution, such as oil of turpentine and many of the essen- 
tial oils. 

334. Paraffine (C^H^^) is a beautiful, semi-transparent, waxy sub- 
stance, which distils over with the last portions of the tar from wood, and 
may be obtained in larger quantity by distilling peat, as well as from the 
mineral known as Boghead cannel. It is also found abundantly in the 
petroleum or mineral naphtha imported from Eangoon. 

In order to extract the paraffine from wood tar, advantage is taken of 
its great resistance to the action of most chemical agents,* for which pur- 
pose the later portions of 'the distillate are moderately heated with con- 
centrated sulphuric acid, which decomposes and chars most of the 
substances mixed with the paraffine, and allows the latter to collect as 
an oily layer upon the surface ; this is allowed to cool and solidify, when 
it may be purified by pressure between blotting paper, and solution in -a 
hot mixture of alcohol and ether, from which it is deposited, on cooling, 
in brilliant plates. 

Paraffine fuses at 110° F., and may be distilled at a higher temperature; 
it burns, like wax, with a very luminous flame, and is employed as a sub- 
stitute for wax in the manufacture of candles. It is insoluble in water, 
and dissolves sparingly in alcohol, ether being the best solvent for it. 

It will be seen from the formula above given for paraffine, that the 
exact number of atoms of carbon and hydrogen contained in it is 
unknown, since it does not form definite compounds with other sub- 
stances, and therefore its exact molecular weight cannot be ascertained ; 
it is known, however, to belong to the marsh-gas series. 

The substance known as paraffine oil, which is used for lubricating 
machinery, is the less volatile portion of the hydrocarbons obtained by 

* To which it owes its name, from parum, little; affinis, allied, 



PETROLEUM. 463 

the destructive distillation of Boghead cannel (found at Bathgate, near 
Edinburgh). The more volatile portion of the hydrocarbons so obtained 
is employed for illuminating purposes. 

Acetone will be described hereafter. 

Of the other products of the destructive distillation of wood enumerated at p. 460, 
some have been described amongst the products obtained from coal, and the remainder 
have been but little studied, and have not received any useful application. 

Eupione (C 5 H 12 ) is a liquid ligbter than water, and boiling at 116° F. 

Kapnomor is an oily liquid, which boils at 360°. 

Picamar is another oily liquid, heavier than water. 

Cedriret is a red crystalline substance. 

Pittacal is a blue solid. 

Stockholm tar is collected during the carbonisation of pine wood, con- 
taining a large quantity of resin, the tar running off through an aperture 
at the lower part of the pit, in which the imperfect combustion of the 
wood is carried on. It differs from ordinary tar in containing large quan- 
tities of resin and turpentine, the latter being separated from it by distil- 
lation, and the residue constituting the pitch of commerce. 

Petroleum. — There are found, in different parts of the earth, generally 
in or near the coal-formations, several solid or liquid hydrocarbons, pro- 
bably formed during the conversion of vegetable remains into coal, some 
of which have received useful applications. 

The Rangoon tar has already been noticed as containing a considerable 
quantity of paraffine ; the liquid part of this tar, after distillation and 
treatment with oil of vitriol to remove hydrocarbons of the benzole series,* 
is the liquid in which potassi am and sodium are . preserved ; it is com- 
monly called petroleum or rock-oil, and appears to be a mixture of several 
hydrocarbons. Petroleum is also employed occasionally as a solvent for 
caoutchouc and resinous substances. In the neighbourhood of the Cas- 
pian sea there are several springs from which rock-oil flows, together with 
water, from the surface of which it is skimmed and sent into commerce. 

American petroleum. — Within the last few years abundant supplies of 
petroleum have been obtained from wells and springs in Pennsylvania 
and Canada, and the demand for it to serve as an illuminating agent, and 
for the lubrication of machinery, has created a new branch of commerce, 
giving rise to the rapid growth of " oil cities" in the neighbourhood of the 
wells. These rock-oils have a very peculiar unpleasant odour, and appear 
to consist chiefly of hydrocarbons belonging to the homologous series of 
which marsh-gas (CH 4 ) is a member. Thus, the Pennsylvanian petroleum 
has furnished the hydrocarbons, C 4 H l0 , C 5 H 12 , C 6 H 14 , C 7 H 16 , C 8 H ]8 , C 9 H 2U . 
In addition to these, the hydrocarbons, C 10 H 20 , C n H 22 , C 12 H 24 , homologous 
with olefiant gas (C 2 H 4 ), have been obtained from it. Some of the mem- 
bers of the benzole series appear also to be present in the Canadian 
petroleum. 

The mineral substance known as bitumen or asphaltum contains a 
hydrocarbon, apparently isomeric with oil of turpentine, together with a 
resinous substance, and a black matter resembling pitch, and containing 
oxygen. It is employed for making water-proof cements and black var- 
nishes, being dissolved for this purpose in turpentine. 

Bituminous shale, when distilled, furnishes products which, as far as 
they are known, are closely allied to those obtained from wood and coal. 

* These hydrocarbons, when treated with oil of vitriol, form acids which are soluble in 
water. Thus benzole is converted into sulphobenzolic acid, HC 6 H 5 .S0 3 . 



464 OIL OF TURPENTINE. 

Oil op Turpentine and Substances Allied to it. 

335. Turpentine is the generic name given to the viscous exudation 
obtained by incising the bark of various species of pine. Several varieties 
of turpentine are met with in commerce, of which the two best known 
are the common turpentine which is obtained from the Scotch fir, and 
Venice turpentine from the ]arch. 

These are both solutions of colophony or common rosin (C 20 H 30 O 2 ) in 
the essential oil of turpentine (C 10 H 16 ), and when distilled, yield from 
75 to 90 per cent, of rosin, which remains in the retort, and from 25 
to 10 per cent, of the essential oil, commonly sold as spirits of turpentine. 

This essence of turpentine boils at 320° E., and floats upon water (sp. 
gr. 0*864), in which it is very sparingly soluble, its proper solvents being 
alcohol and ether. Its great inflammability renders it useful as a fuel for 
lamps, but the large proportion of carbon which it contains causes it to 
burn with a smoky flame, rendering it necessary either to employ lamps 
constructed especially to afford an extra supply of air to the flame, or to 
mix it with a certain proportion of alcohol. Gampliine is distilled from 
the turpentine of the Boston pine. 

The property of turpentine to dissolve resinous and fatty substances 
renders it exceedingly useful in the preparation of paints and varnishes, 
and for the removal of such substances from fabrics. It is also an excel- 
lent solvent for caoutchouc. 

One of the most remarkable features of this essential oil is the facility with which 
it changes into isomeric or metameric modifications, exhibiting great differences 
in their physical and chemical properties. 

When heated in a closed vessel to about 480° F. for some hours, oil of turpentine 
is converted into two isomeric modifications differing greatly from the original oil in 
the temperature at which they boil ; for whilst oil of turpentine distils over entirely 
at 320° F., one of these modifications, known as isoterebenthene, boils at 350° F., and 
the other, metaterebenthene, at 660°. 

When digested, in the cold, with a small proportion of oil of vitriol, oil of tur- 
pentine yields terebene and colophene, the former boiling at 320° F., but differing 
from oil of turpentine in its odour, which resembles thyme, and in its want of action 
upon polarised light. 

Colophene has a far higher boiling point (600°), and is much heavier than tur- 
pentine (sp. gr. 0*940), from' which it is also distinguished by its indigo-blue colour 
when seen obliquely, though it is colourless by directly transmitted light. More- 
over, the specific gravity of the vapour of colophene is 9 '52, whilst that of turpentine 
is 4 '76, or one-half that of colophene, rendering it probable that if the composition of 
turpentine be C^H^ (= 2 vols.), that of colophene is C 20 H 32 (= 2 vols.), a relation 
expressed by saying that colophene is polymeric with turpentine. Colophene is also 
obtained by the distillation of colophony, 

The ordinary oil of turpentine appears to be really itself a compound of two 
isomeric hydrocarbons, for when hydrochloric acid gas is passed into it, two distinct 
isomeric compounds are formed, both expressed by the formula, C 10 H 16 .HC1, but one 
being a solid, and the other a liquid even at 0° F. 

The solid compound, which is known as artificial camphor or hydrochlorate ofdadyle, 
forms white prismatic crystals very similar to camphor, and when its vapour is 
X>assed over heated quick-lime, the latter removes the hydrochloric acid, and the 
hydrocarbon known as camphilene or dadyle @k$, a pine-torch) is obtained, which is 
isomeric with oil of turpentine, but boils at 273 u instead of 320° F., and is without 
any action upon polarised light. 

The liquid compound formed by the action of hydrochloric acid upon oil of tur- 
pentine is called hydrochlorate of pcucyle; and when distilled with quick-lime yields 
terebilene or peucyle {<xtvKn, the pine), also isomeric with oil of turpentine, but without 
action on polarised light. 

Although oil of turpentine is not miscible with water, it is capable of forming 
three compounds with it in different proportions. When the oil is long kept in 
contact with water, crystals are deposited which have the composition C 10 H 16 .3H,,O ; 



ESSENTIAL OILS. 465 

boiling water dissolves these, and deposits them in a prismatic form on cooling. The 
crystals fuse at about 217° F. ; and when further heated, lose a molecule of water, 
yielding another crystalline hydrate, which sublimes without alteration at about 
480° F. When exposed to the air this hydrate again absorbs a molecule of water. 

By distilling the aqueous solution of either of the preceding hydrates with a 
little sulphuric acid, a liquid hydrate smelling of hyacinths is obtained ; it contains 
(C 10 H 16 ) 2 H 2 O, and is called terpinole. 

When oil of turpentine is exposed to the air, it slowly becomes solid, 
absorbing oxygen, and becoming converted into resinous bodies. 

Common rosin or colophony* — This substance is composed of two 
isomeric acids known as sylvic and pinic. When common rosin is treated 
with cold alcohol, the greater portion of it is dissolved; and if the 
alcohol be evaporated, it leaves an amorphous substance, which is pinic 
acid. The residue, left undissolved by cold alcohol, is dissolved by hot 
alcohol, and deposited in colourless prisms, which are sylvic acid. These 
acids have the composition HC 20 H 29 O 2 . The pinate and sylvate of soda 
obtained by dissolving rosin in solution of soda or carbonate of soda, are 
largely used in the manufacture of yellow soap, and of the size for paper- 
makers. By distilling common rosin with the aid of superheated steam, 
it is obtained nearly free from colour. 

336. The turpentine series of hydrocarbons. — Oil of turpentine is the 
representative of a large class of hydrocarbons, derived like itself from 
the vegetable kingdom, and all having a percentage composition corres- 
ponding to the formula C 10 H 16 . All the individuals of this group resemble 
turpentine in their liability to suffer conversion into isomeric modifica- 
tions, in their solidification by absorption of oxygen when exposed to 
the air, in their combination with water to form crystalline hydrates, and 
above all, in their tendency to form artificial camphors by combining with 
hydrochloric acid. 

The oils of bergamotte, birch, camomile, carraway, cloves, hops, juniper, 
lemons, orange, parsley, pepper, savin, tolu, thyme, and valerian, contain 
the same hydrocarbon C 10 H 16 , generally accompanied, in the natural oil, 
by the product of its oxidation, bearing a relation to the hydrocarbon 
similar to that which colophony bears to turpentine. 

These essential oils are generally extracted from the flowers, fruit, 
leaves, or seeds, by distillation with water, the portion of the plant 
selected being suspended in the still by means of a bag or perforated 
vessel, so that there may be no danger of its being scorched by contact 
with the hot sides of the still, and so contaminating the distillate with 
empyreumatic matters (iixTrvpcvoi, to scorch). The water which distils over 
always holds a little of the essential oil in solution, and it is in this way 
that the fragrant distilled waters of the druggist are obtained. When the 
essential oil is present in large proportion, it collects as a separate layer 
upon the surface of the water, from which it is easily decanted. The oil 
which is dissolved in the water may be separated from it by saturating 
the liquid with common salt, when the oil rises to the surface, or by 
shaking it with ether, which dissolves the oil and separates from the 
water, the ethereal solution floating upon its surface, and leaving the oil 
when the ether is evaporated. 

In cases like that of jasmine, where the delicate perfume of the flower 
would be injured by the heat, the flowers are pressed between woollen 

* Colophon, a city of Ionia. 

2 G 



466 CAMPHOE. 

cloths saturated with oil of poppy seeds, which thus acquires a powerful 
odour of the flower. 

Bisulphide of carbon is also sometimes employed as a solvent for extract- 
ing the essential oils. 

Oil of peppermint contains a hydrocarbon called menthene (C 10 H 18 ) ; 
essence of cedar-wood contains cedrene (C 16 H 26 ). 

337. Camphors. — Closely allied to the essential oils are the different 
varieties of camphor, which appear to be formed by the oxidation of 
hydrocarbons corresponding to the essential oils. 

Common camphor (C 10 H 16 O) is found deposited in minute crystals in 
the wood of the Laurus campliora or camphor laurel, from which it is 
obtained by chopping up the branches and distilling them with water in 
a still, the head of which is filled with straw, upon which the camphor 
condenses. It is purified by subliming it in large glass vessels containing 
a little lime. 

Camphor passes into vapour easily at the ordinary temperature of the 
air, and is deposited in brilliant octahedral crystals upon the sides of the 
bottles in which it is preserved. It fuses at 347° F., and boils at 399° P., 
and is very inflammable, burning with a bright smoky flame. It is some- 
times dissolved in the oil used for the lamps of magic lanterns, to increase 
its illuminating power. Camphor is lighter than water (sp. gr. 0*996), 
and whirls about upon its surface in a remarkable way, dissolving mean- 
while very sparingly (1 part in 1000), alcohol and ether being its appro- 
priate solvents. 

When distilled with anhydrous phosphoric acid, camphor loses a molecule of water, 
and yields the hydrocarbon cymole (C 10 H U ) homologous with benzole. 

Borneo camphor (C^H^O) is obtained from the exudation of the Dryobalanops 
camphora. "When this exudation is distilled, a hydrocarbon called borneene (C 10 H 16 ), 
isomeric with oil of turpentine, first passes over, and afterwards the camphor, which 
is neither so fusible nor so volatile as!ordinary camphor, and emits quite a different 
odour ; it also crystallises in prisms instead of octahedra, and may be converted 
into ordinary camphor by the action of nitric acid, which oxidises two atoms of 
hydrogen — 

C 10 H 18 O {Borneo camphor) — H 2 = C 10 H 16 O (Common camphor). 

The Borneo camphor appears to have been formed by the combination of borneene 
with water, for if this hydrocarbon be distilled with solution of potash, it combines 
with a molecule of water, and is converted into the camphor. On the other hand 
when Borneo camphor is distilled with anhydrous phosphoric acid, it loses a molecule 
of water, and yields borneene. It is interesting to remark that this hydrocarbon is 
also found in the essential oil of valerian. 

The oil of camphor which accompanies the camphor distilled from the camphor 
laurel, contains an atom of oxygen less than common camphor, its formula being 
(C 10 H 16 ) 2 O. 

338. Balsams. — The vegetable exudations known as balsams are mix- 
tures of essential oils with resins and acids probably produced by the 
oxidation of the oils. 

Balsam of Peru contains an oily substance termed cinnameine 
(C 27 H 26 4 ), a crystalline body, styracine (C ? H 8 0), a crystalline volatile acid, 
the cinnamic (C 9 H 8 2 ), and a peculiar resin. 

Balsam of Tolu also contains cinnamic acid and styracine, together 
with certain resins, which appear to have been formed by the oxidation 
of styracine. 

Storax f also a balsamic exudation, contains the same substances, accom- 
panied by a peculiar hydrocarbon, which has been named styrole, and has 
the composition C 8 H 8 . This liquid is characterised by a remarkable 



RESINS. 467 

change which it undergoes when heated to about 400° F., being converted 
into a colourless solid, metastyrole, which is polymeric with styrole, into 
which it is reconverted by distillation. 

339. Resins. — Colophony is the best known member of the class of 
resins, which are generally distinguished by their resinous appearance^ 
fusibility, inflammability, burning with a smoky flame, insolubility in 
water, and solubility in alcohol. 

As to their chemical composition, they are all rich in carbon and hydro- 
gen, containing generally a small proportion of oxygen, and appear to 
have been formed, like colophony (p. 465), by the oxidation of a hydro- 
carbon analogous to turpentine. 

Most of the resins also resemble colophony in their acid characters, 
their alcoholic solutions reddening blue litmus paper, and the resins 
themselves being soluble in the alkalies. This is the case with sandarach 
and guaiaeum resin, the former of which contains three, and the latter 
two, resinous acids. 

Copal appears to contain several resins, some neutral and some acid, 
and is distinguished by its difficult solubility in alcohol, in which it can 
be dissolved only after long exposure to the vapour of the solvent ; but 
if it be exposed to the air for some time, at a moderately high tempera- 
ture, it absorbs oxygen, and becomes far more easily soluble. Copal is 
readily dissolved by acetone. Animi and elemi resins are somewhat 
similar in properties to copal. 

All these resins are used in the manufacture of varnishes. 

Guaiaeum resin is distinguished by its tendency to become blue under 
the influence of the more refrangible and chemically active (violet) rays 
of the solar spectrum, as well as under that of certain oxidising agents, 
such as chlorine and ozone. 

Lac, so much used in the arts, belongs to the class of resins, being the 
exudation of certain tropical trees punctured by an insect. In its crude 
natural state, encrusting the small branches, it is known as stick-lac, and 
has a deep red colour ; when broken off the branches and boiled with 
water containing carbonate of soda, it furnishes a red colouring matter, 
very largely used in dyeing, leaving a resinous residue termed seed-lac, by 
fusing which the shell-lac is obtained. This resin is very complex, con- 
taining several distinct resinous bodies. It is largely used in the manu- 
facture of hats, of sealing-wax, and of varnishes. The lacquer applied to 
brass derives its name from this resin, being an alcoholic solution of shell- 
lac, sandarach, and Venice turpentine. Indian ink is made by mixing 
lamp-black with a solution of 100 grains of lac in 20 grains of borax and 
4 ounces of water. 

Amber, a fossil resinous substance, more nearly resembles this class of 
bodies than any other, and contains several resinous bodies. It is distin- 
guished by its insolubility, for alcohol dissolves only about one-eighth, 
and ether about one-tenth of it. After fusion, however, it becomes soluble 
in alcohol, and is used in this state for the preparation of varnishes. 

The distinguishing peculiarity of amber is, that it yields succinic acid, 
H 2 C 4 H 4 4 (succinum, amber), when digested with alkalies, distilled, or 
oxidised by nitric acid ; in the latter case ordinary camphor is formed at 
the same time. 

Succinic acid is also found in some of the resins of coniferous trees, and 
in the leaves of the wormwood. It is among the products of the action 



468 



BENZOIC ACID. 



of nitric acid upon most fatty and waxy substances, and is present in 
wines and other fermented liquors, being produced during the fermenta- 
tion of sugar. The acid is characterised by the cough-provoking vapour 
which it emits when heated. * 

Varnishes are prepared by dissolving resins in alcohol, or wood spirit, 
or acetone,t a little turpentine or some fixed oil being added to prevent 
the resin from cracking when the solvent has evaporated. In order to 
promote the solution of the resin, it is usually powdered before being 
treated with the solvent, and mixed with coarsely powdered glass to pre- 
vent it from becoming lumpy. Methylated spirit is now very generally 
used for the preparation of varnishes ; it is simply spirit of wine, to which 
a little wood naphtha has been added, to deter persons from drinking 
it, and to prevent other frauds upon the Excise. 

Benzoin, or gum benzoin, as it is erroneously called, is also a vege- 
table resinous product, and is distin- 
guished by the presence of benzoic 
acid (HC 7 H 5 2 ), which may be ob- 
tained from it by heating the resin 
in an iron or earthen vessel (fig. 287) 
covered with a perforated sheet of 
stout paper, over which a drum or 
cone of paper is tied. When the heat 
of a sand-bath is applied, benzoic acid 
rises in vapour, and is condensed in 
beautiful feathery crystals in the 
paper drum. It may also be ex- 
tracted by boiling the resin with water 




Fig. 287. 



and lime, when the benzoic acid is 



dissolved in the form of benzoate of 
lime Ca(C 7 H 5 2 ) 2 , and being but sparingly soluble in water, may be pre- 
cipitated by adding hydrochloric acid to the filtered solution. 

Benzoic acid is generally recognised by its feathery appearance and 
peculiar agreeable odour, though this does not really belong to the acid, 
but to a little essential oil which is not easily separated ; the vapour of 
the acid itself is very irritating and produces coughing. It fuses when 
moderately heated, and burns with a smoky flame. Benzoic acid dissolves 
in about 200 parts of cold and 25 parts of boiling water. Alcohol and 
ether dissolve it easily. 

The salts of benzoic acid, or benzoates, have no practical importance, 
but the behaviour of benzoic acid when distilled with an excess of lime 
or baryta has already been referred to as furnishing that important hydro- 
carbon, benzole (see p. 455). 



Oil of Bitter Almonds, and its Derivatives. — Benzoyle Series. 

340. Benzoic acid results from the oxidation of the essential oil of 
bitter almonds (C 7 H 6 0), which slowly absorbs an atom of oxygen from 
the air, and is converted into benzoic acid (C 7 H 6 2 ). 

* Succinic acid has been obtained artificially by the action of cyanide of potassium upon 
a solution of chloropropionic acid ; 



KCN 



C 3 H 5 C10 2 + 
Chloropropionic. 

f Acetone readily dissolves copal, mastic, taid sandarach 



+ 2H 2 = C 4 H 6 4 + KC1 + NH 3 . 
Succinic. 



OIL OF BITTER ALMONDS. 46 ( J 

The formation of the essential oil of bitter almonds is one of the most 
interesting processes of vegetable chemistry. 

Both the bitter and the sweet almond contain a large quantity of a 
fixed oil, which may be extracted from them by pressure, but which has 
no particular taste or odour, and differs entirely from the essential oil of 
bitter almonds, being, in fact, very similar to ordinary olive oil. The 
residue, or almond-cake, which is left after expressing the oil, contains, in 
the case of the bitter almond only, a bitter principle, amounting to about 
^o-th of the weight of the almond, which may be extracted from the cake 
by hot alcohol, and may be crystallised from the solution ; this substance 
is called amygdaline, and is represented by the formula C 20 H 27 NO 115 the 
crystals containing, in addition, three molecules of water. 

Now, if the residue left after extracting the amygdaline with alcohol 
be mixed with water and distilled, it does not yield any essential oil, 
although this may be obtained in abundance from the original cake after 
maceration in water, particularly if it be digested with water for several 
hours before distillation. 

The sweet almond, which contains no amygdaline, does not afford any 
essential oil when distilled with water, showing that the amygdaline is 
really the source of the essence. Again, if boiling water be poured over 
the bitter almond cake, no essential oil is produced, even when the mix- 
ture is allowed to stand for some time, but if to this mixture there be 
added an emulsion of sweet almonds prepared with cold water, the bitter 
almond oil is at once formed, which is not the case, however, if the emul- 
sion be prepared with boiling water. 

From this it is evident that a substance exists in both sweet and bitter 
almonds which is capable of developing the essence from the amygdaline 
contained in the latter, but which loses its power when acted upon by 
hot water. This may be s^ill further proved by dissolving pure amygda- 
line in water, and adding an emulsion of sweet almonds, when the essence 
is at once produced. 

When the emulsion of sweet almonds is filtered and mixed with alcohol, 
a white substance resembling albumen is precipitated, which contains 
carbon, hydrogen, nitrogen, and oxygen, and very easily putrefies when 
exposed to the air in a moist state. If this substance, which is called 
emulsine or synaptase (ywaTTTw, to hring into action), be dissolved in cold 
water, and mixed with a solution of amygdaline, the oil of bitter almonds 
is soon formed in abundance, but if the solution of emulsine be boiled, it 
is no longer capable of developing the essence. On examining the solu- 
tion of amygdaline in which the essential oil has been produced by the 
action of emulsine, it is found to contain, in addition, hydrocyanic acid 
(CHJST), grape-sugar (C 6 H 14 7 ), and formic acid (CH 2 2 ), so that the 
decomposition may be thus represented — 
2C 20 H 27 £rO u - 4C 7 H 6 + 2CHN + C 6 H u 7 + 4CH 2 2 + 3H 2 . 

Amygdaline. Bitter^almond Hydrocyanic Grape sugai . Formic 

The formation of the essential oil of bitter almonds must be regarded, 
therefore, as dependent upon a species of fermentation or metamorphosis 
of the bitter principle amygdaline, induced by contact with an albuminous 
substance, emulsine, itself very prone to undergo decomposition when 
exposed to air in the presence of moisture. 

This essential oil may also be obtained from laurel leaves, and from the 
kernels of most stone fruit. 



470 BENZOYLE SERIES. 

When the oil of bitter almonds is distilled over, it is accompanied by 
the hydrocyanic acid formed at the same time, and it is this which ren- 
ders the ordinary commercial oil so powerful a poison, for if it be purified 
by distillation from a mixture of lime and chloride of iron (see Prussian 
blue), which retains the hydrocyanic acid, it becomes comparatively harm- 
less. A better process for obtaining the pure oil of bitter almonds con- 
sists in shaking the crude oil with an equal volume of a strong solution 
of bisulphite of soda, with which it forms a white crystalline compound. 
If this be distilled with solution of carbonate of soda, the pure oil passes 
over. 

The poisonous properties of laurel-water, and similar preparations, are 
also due to the presence of hydrocyanic acid. 

The crude essential oil of bitter almonds also contains a crystalline substance called 
benzoine (C 14 H 12 2 ), which is interesting as being polymeric with the essence, into 
which it may be converted by passing its vapour through a red-hot tube. The crude 
oil may be entirely converted into this substance by shaking it with an alcoholic 
solution of potash. 

When the pure essential oil of bitter almonds (C 7 H 6 0) is acted upon by dry 
chlorine, it evolves hydrochloric acid, and becomes converted into a colourless liquid, 
having an odour of horse-radish, . and containing C 7 H 5 C10, an atom of hydrogen 
having been removed, and its place filled by an atom of chlorine. If this liquid be 
acted upon by the bromides, iodides, cyanides, or sulphides of the metals, the 
chlorine is removed in its turn, the vacancy being filled up by bromine, iodine, 
cyanogen or sulphur, compounds being obtained which have the formulae — 

C 7 H 5 BrO, C 7 H 5 IO, C 7 H 5 CyO, (C 7 H 5 0) 2 S. 

When boiled with water, this chlorine compound is converted into benzoic acid — 

C 7 H 6 C10 + H 2 = C 7 H 5 2 .H + HC1. 

On comparing the composition of these compounds with that of the essential oil 
from which, they are derived, our attention is called to the existence of C 7 H 6 in all 
of them — • 

Oil of bitter almonds, . (C 7 H 5 0)H 

Benzoic acid, . . . (C 7 H 6 0)HO 

Chlorine compound, . (C 7 H 5 0)C1 

Bromine „ . . (C 7 H 5 0)Br, &c. 

This circumstance led many chemists to assume the existence in these compounds 
of the radical benzoyle (C 7 H 5 0), capable of playing the part of an elementary sub- 
stance in uniting with oxygen, chlorine, &c, and therefore resembling the elements 
in its chemical tendencies, from which resemblance it is spoken of as a quasi-element 
or compound radical. 

If this radical be represented by Bz, the formation of the members of the benzoyle 
scries from oil of bitter almonds will be simply and easily traced. 



Oil of bitter almonds, hydride of benzoyle, 


BzH 


Benzoic acid, benzoyle hydrate, 


BzHO 


Chloride of benzoyle 


BzCl 


Bromide ,, .... 


BzBr 


Iodide ,, .... 


Bzl 


Cyanide ,, .... 


. BzCy 


Sulphide ,, 


Bz 2 S 



The radical benzoyle itself has been recently obtained in' a separate state by the 
action of sodium on chloride of benzoyle. It forms prismatic crystals, which fuse 
easily, and may be sublimed without decomposition. They are sparingly soluble in 
alcohol and ether. The formula C 7 H 5 should be doubled to express correctly a 
molecule of this radical (see Alcohol radicals). 

It will be noticed that benzoic anhydride is not included in the above enumeration 
of the benzoyle series. This compound, which may be represented as Bz a O, or 
(C 7 H 6 ) a O, is obtained by heating benzoate of soda with chloride of benzoyle — 

NaBzO + BzCl 



GLUCOSIDES. 471 

This substance has no acid properties whatever. It does not dissolve in cold 
water, but if boiled with water, is slowly converted into benzoic acid. 

When oil of bitter almonds is decomposed by hydrate of potash dissolved in 
alcohol, it yields benzoic alcohol (C 7 H 8 0), which will be more particularly noticed 
hereafter. 

341. Very closely connected with the essential oil of bitter almonds are the essences 
of cinnamon and cassia, which consist chiefly of an oxidised essence, represented 
by the formula C 9 H 8 0, and convertible by boiling with nitric acid into the essence 
of almonds. By heating the essence of cinnamon with hydrate of potash, it is 
oxidised and converted into cinnamate of potash — 

C 9 H 8 + KHO = KC 9 H 7 2 + H a . 

. Oil of cinnamon. <*%££« 

On dissolving this salt in water, and adding an acid, the cinnamic acid is precipi- 
tated in feathery flakes, closely resembling benzoic acid, both in appearance and 
chemical characters.* 

The same reasons exist as in the case of the benzoyle series, for assuming the 
existence in the compounds derived from oil of cinnamon of the radical cinnamyle, 
C 9 H 7 0, so that the oil of cinnamon would be a hydride of cinnamyle (C 9 H 7 0)H, and 
cinnamic acid the cinnamyle hydrate (C 9 H 7 0)HO. 

Essential oil of cummin is a mixture of the hydrocarbon cymole (C 10 H 14 ), which has 
been already noticed, with an oxidised essence, C 10 H 12 O, which is closely analogous 
to those of almonds and cinnamon, and is called hydride of cumyle (C 10 H n O)H ; 
when acted upon by oxidising agents it yields cuminic acid (HC 10 H u O 2 ), which 
resembles benzoic acid, but is characterised by an odour similar to that of the bug. 
From the hydride of cumyle an oily compound has been obtained, which is poly- 
meric with the supposed radical cumyle, having the composition C 20 H 22 O 2 , and that 
it is really composed of a double molecule of that radical is rendered very probable 
by its behaviour when fused with hydrate of potash, its hydrogen converting one 
molecule of cumyle into hydride of cumyle, whilst its oxygen converts the other into 
cuminic acid — 

C 20 H 22 O a + KHO = (O 10 H n O)H + K(C 10 H u O)O. 

H c y uml d ll 0f Cuminate of potash. 

The essential oils of aniseed, fennel, and tarragon contain, in addition to a hydro- 
carbon isomeric with turpentine, a solid crystalline oxidised essence (C 10 H 12 O) 
isomeric with the hydride of cumyle. That this substance is not hydride of cumyle, 
however, is at once proved by the action of oxidising agents, which convert it into 
hydride of anisyle (C 8 H 7 2 )H, and anisic acid, HC 8 H 7 3 , the latter being isomeric 
with winter-green oil (see p. 462). 

342. Salicine and its derivatives — Glucosides. — Oil of spircea, or 
meadow sweet, consists chiefly of the compound (C 7 H 6 2 ) isomeric with 
benzoic acid ; this compound is easily obtained artificially by the oxidation 
of salicine, a bitter substance extracted from willow bark, by boiling it in 
water, removing the colouring matter and tannin from the solution by 
boiling with hydrated oxide of lead, precipitating the excess of lead by 
bydrosulphuric acid, and evaporating the filtered liquid, when the salicine 
crystallises out, and may be obtained by recrystallising from alcohol, 
in beautiful white needles having the composition C 13 H 18 7 . 

Salicine is sparingly soluble in cold water and insoluble in ether, but 
dissolves readily in boiling water and in alcohol. It is readily distin- 
guished by the red colour which it gives with concentrated sulphuric acid, 
which manifests its presence when applied to the inner bark of the willow. 
When distilled with dilute sulphuric acid and bichromate of potash, it 
yields the oil of spiraea. 

The changes suffered by salicine when boiled with a dilute mineral acid (as sul- 
phuric) are very remarkable, for after the boiling has been continued for a few 

* Oil of bitter almonds has been converted into cinnamic acid by heating it with acetic 
oxy chloride ; C 7 H 6 +(C 2 H 3 0)C1=C 7 H 5 (C 2 H 3 0)0 + HC1. 



472 



SALICYLE SERIES. 



minutes, the solution is found to contain grape-sugar, together with a crystalline 
substance called saligenine, which is distinguished by the intense blue colour which 
it gives with perchloride of iron. The change is easily explained, for the addition 
of 2 molecules of water to salicine would provide the elements of grape-sugar and 
saligenine — 

C 13 H 18 7 + 2H 2 = C 7 H 8 2 + C 6 H 14 7 . 
Salicine. Saligenine. Grape-sugar. 

Emulsine or synaptase is capable of effecting this change in salicine, 
be remembered that grape-sugar is one of the products of the action of 
upon amygdaline. If the ebullition of the diluted acid be continued 
of time, the liquid deposits a resinous substance, saliretine, which is i 
oil of bitter almonds (C 7 H 6 0). 

A very striking example of the stability of types, notwithstanding* the substitution 
of one element for another, is found in the circumstance that salicine, under the 
influence of chlorine, yields three different products containing chlorine in place 
of hydrogen, and that when these are boiled with dilute acids, they yield other 
products containing chlorine, and bearing the same relation to their chlorinated 
primitive which saligenine and saliretine respectively bear to salicine. 

Thus we have — 



Salicine, . . . 
Chlorosalicine, . 

Dichlorosalicine, 

Trichlorosalicin e, 



H 3 
»C1 

H 3 

■< H x 
' 13 Ch 



e 13 cT I °7 



c 13 3-[o 7 



15 o 7 



Saligenine, . . . 
Chlorosaligenine, . 

Dichlorosaligenine, 

Trichlorosaligenine, 



C 7 ^J0 2 
C 7 H«|o 3 



j H 5 

' 7 CL 



0, 



"When salicine is fused with hydrate of potash, the mass dissolved in water, and 
hydrochloric acid added, beautiful needles of salicylic acid (HC 7 H 5 3 ) are separated. 
This acid may also be obtained from the oil of spiraea by a similar process, and it 
will be seen that salicylic acid bears the same relation to this oil as benzoic acid 
bears to oil of bitter almonds — 

Oil of bitter almonds, C 7 H 6 Oil of spiraea, . . . C 7 H 6 2 

Benzoic acid, • . . C 7 H 6 2 Salicylic acid, . . . C 7 H 6 3 . 

Salicylic acid has been obtained in a most interesting manner by the simultaneous 
action of carbonic acid and sodium upon phenole — 

C 6 H 6 + C0 2 + Na = NaC 7 H 5 3 + H. 
Phenole. Salicylate of 

soda. 

Exactly as chemists have been led to consider the bitter almond oil as hydride of 
benzoyle, so they have regarded oil of spiraea as hydride of salicyle (C 7 H 5 2 .H), 
assuming the existence of the radical salicyle (C 7 HgO), of which salicylic acid would 
be the hydrate. "We find this view of the constitution of these compounds sup- 
ported by the circumstance, that when the oil of spiraea is heated with chloride of 
benzoyle, a substance is obtained which may be regarded as composed of the two 
radicals salicyle and benzoyle — 

C 7 H 5 2 .H + C 7 H 5 0.C1 = C 7 H 5 O.C 7 H 5 2 + HC1. 
Oil of spiraea. ^nioyle?* Benzoyle-salicyle. 

From a careful study of the behaviour of salicine under the action of various 
re-agents, the inference has been drawn that it is a compound of saligenine (C 7 H 8 2 ) 
with a substance (C 6 H 10 O 5 ), which becomes converted into grape-sugar, by assimila- 
tion of water, as soon as it is separated from the saligenine. 

Salicine is occasionally employed in medicine as a febrifuge, and is 
a common adulteration of quinine. 

Salicine is the chief member of the class of substances termed glucosides, 
from the presence of grape-sugar (glucose) among their products of decom- 
position. To this class belong several other substances much resembling 
salicine, and, like it, extracted from the barks of different trees. 



SULPHURETTED ESSENTIAL OILS. 473 

343. Populine, (C 20 H 22 O 8 ) is a sweet crystalline substance obtained from the bark 
and leaves of the aspen, and especially interesting from its close connection with 
the benzoyle and salicyle series ; for when boiled with solution of baryta, it is decom- 
posed into benzoic acid (which unites with the baryta) and salicine — 

2C 20 H 22 O 8 + BaO.H 2 = Ba(C 7 H 5 2 ) 2 + 2C 13 H 18 7 . 
Populine. Benzoate of baryta. Salicine. 

Nor is this the only connecting link, for populine yields oil of spirsea when distilled 
with sulphuric acid and bichromate of potash, and when boiled with dilute acids it 
furnishes benzoic acid, saliretine, and grape-sugar — 

C 20 H 22 O 8 + 2H 2 = HC 7 H 5 2 + C 7 H 6 '+ C 6 H 14 7 . 
Populine. Benzoic acid. Saliretine. Grape-sugar. 

In order to explain this production of benzoyle and salicyle compounds from popu- 
line, it is usual to regard this substance as formed from salicine (C 13 H 18 7 ) by the 
introduction of a molecule of benzoyle (C 7 H 5 0), in the place of an atom of hydrogen — 

C 20 H 22 O8 = ^13 H 17( C 7 H 5^)0 7 • 

Populine. Benzoyle-salicine. 

Phloridzine (C 21 H 24 O 10 ) is extracted from the bark of the apple, pear, plum, and 
cherry tree ; it crystallises readily, is slightly bitter, and when boiled with dilute 
acids, yields grape-sugar and a resinous substance called phloretine (C ]5 H u 5 ). Its 
most interesting property is that of forming a red compound (phloridzeine) when 
exposed to the joint influences of air and ammonia — 

C 2 iH 24 O 10 + 3 + 2NH 3 = C 21 H 3o N 2 13 . 

Phloridzine. Phloridzeine. 

This red compound combines with ammonia to form a purple mass with a coppery 
lustre, which dissolves in water with a fine blue colour. The production of this 
colouring matter from phloridzine is an excellent example of that conjoined action 
of air and ammonia by which certain natural colouring matters, such as litmus, are 
formed from substances which are themselves destitute of colour. 

Quercitrine (C 33 H 30 O 17 ) is the yellow colouring matter extracted by alcohol from 
the bark of the quercitron. It is a crystallisable substance, and is decomposed by 
boiling with acids into grape-sugar and a yellow crystalline body called quercetine 
(C 27 H 18 12 ). 

Esculine (C 2] H 24 13 ) is extracted from the bark of the horse-chestnut by boiling 
water. If the tannin and colouring matter be precipitated from the infusion by 
acetate of lead, the filtered liquid treated with sulphuretted hydrogen to remove the 
excess of lead, and the solution, after a second filtration, evaporated, the esculine is 
obtained in colourless needles. It is remarkable for its fluorescence ; although its 
solution is colourless by transmitted light, it appears of a beautiful deep blue colour 
when viewed at certain angles. This substance is -also a glucoside, for when 
boiled with dilute acids, it yields grape-sugar and a crystalline substance known as 
esculetine. 

C 21 H 24 13 + 5H 2 = C 9 H 6 4 + 2C 6 H 14 7 . 
Esculine. Esculetine. Grape-sugar. 

P amine also occurs in the horse-chestnut bark, but in far larger quantity in the 
bark of the ash. It is distinguished from esculine by exhibiting a green 
fluorescence. 

Saponine is a substanee closely allied to the glucosides, and is found in the soap- 
wort, the fruit of the horse-chestnut, the pimpernel, the root of the pink, and in 
many other plants. It may be extracted by boiling alcohol, which deposits it in an 
amorphous state on cooling. Saponine is soluble in water, and its solution is char- 
acterised by the readiness with which it lathers, like soap and water, although it 
may contain a very small quantity of saponine. This property leads to the use of 
decoctions containing it, such as those of the soap-wort, and of the soap-nut of 
India, for the purpose of cleansing certain delicate fabrics. 

Picrotoxine (C 5 H 6 2 " 

of Cocculus indicus are due. It appears to have feeble acid tendencies, and is ex- 
tracted from an acidified solution by shaking with ether. On evaporating the 
ethereal solution it leaves prismatic needles of an intensely bitter taste. 

344. Essential oils containing sulphur — Allyle series. — The essen- 
tial oils of asafo°Uda, of cress, garlic, horseradish, leeks, mustard, onions, 



474 ALLYLE SERIES. 

and radishes, differ from those which have been already described by con- 
taining sulphur. 

Those of asafoetida, cress, garlic, leeks, onions, and radishes, are com- 
posed essentially of the same substance, represented by the formula 
C 6 H 10 S. The essence of mustard and that of horseradish are composed of 
C 4 H 5 NS. 

The chemistry of the origin of essential oil of mustard is analogous to 
that of essence of almonds. The oil is obtained from the seeds of the 
black mustard after removing the fixed oil (which has no pungency what- 
ever) by pressure; on moistening the crushed seed with water, the pro- 
duction of the essential oil is indicated by its peculiar odour, and it may 
be separated from the seeds by distillation. The mustard seeds con- 
tain a salt of potash with a peculiar acid called myronic acid,* 
(H 2 C 20 H 38 ]Sr 2 S 4 O 19 ), together with a substance similar to the emulsine of 
almonds, which has been termed myrosine, and is capable of inducing the 
decomposition of the myronic acid, and the consequent production of 
essence of mustard, just as the emulsine of almonds developes the essential 
oil by the decomposition of the amygdaline ; in the case of mustard, how- 
ever, the nature of the decomposition has not been so clearly made oat, 
but is probably represented by the equation — 

HAfAAS.Ou = 2C 4 H 5 NS + 2C 6 H 14 7 + H 2 + 2S0 2 . 

Myronic acid. "SSSf GluCOse - 

The essence of mustard has been produced artificially in a very inter- 
esting and remarkable manner, 

When glycerine (the sweet principle of the fats and fixed oils) is dis- 
tilled with the biniodide of phosphorus, a colourless ethereal liquid is 
obtained, which has the composition C 3 H 5 I,.and is called iodide of allyle, 
because when distilled with sodium, it yields iodide of sodium and a 
volatile liquid composed of C 3 H 5 , and called allyle, in allusion to its pecu- 
liar odour (allium, garlic). The formation of iodide of allyle is explained 
by the following equation — 

2C 3 H 8 3 4- 2PI 2 = 2C 3 H 5 I + 3H 2 O.P 2 3 + I 2 . 

Glycerine. Iodide of allyle. 

When iodide of allyle is distilled with sulphocyanido of potassium, 
an oily liquid is obtained, identical in properties and composition with 
oil of mustard, which must therefore be regarded as a sulphocyanide of 
allyle, its artificial production being thus explained — 

C 3 H 5 I + K(CISrS) - C 8 H 6 .OTS 4- KI. 

Additional interest is created in this artificial formation of oil of mus- 
tard when it is found to be convertible into oil of garlic, by being heated 
with sulphide of potassium, when sulphocyanide of potassium is formed 
at the same time, thus — 

2(C 3 H 5 .OTS) 4- K 2 S = (C 3 H 5 ) 2 S 4- 2K(CNS) . 

Essence of mustard. Essence of garlic. JjJS^ 

Hence it is inferred that the essence of garlic is a sulphide of allyle, of 
which essence of mustard is a sulphocyanide. 

* From ixvpov, an unguent. 



GUM-RESINS, 475 

The oil of Cochlearia officinalis is sometimes sold as essential oil of 
mustard, which it much resembles ; but the former is sulphocyanide of 
butyle C 4 H 9 .CNS, and boils at 160° C, whilst the latter boils at H7° C. 

A considerable number of compounds are included in the allyle series, but are not 
at present possessed of any practical importance. 

The allylic alcohol (C 3 H 6 HO) is interesting as the prototype of a new class of 
alcohols, parallel with that represented by common alcohol (C 2 H s HO). In order 
to obtain it, the iodide of allyle is decomposed by oxalate of silver, when oxalate of 
allyle is obtained — 

2C 3 H 5 I + Ag 2 C 2 4 = (C 3 H 5 ) 2 C 2 4 + 2AgI . 
Iodide of allyle. Oxalate of allyle. 

By treating oxalate of allyle with ammonia, allylic alcohol and oxamide are 
obtained — 

(C 3 H 6 ) 2 C 2 4 + 2NH 3 = 2C 3 H 5 HO .+ C 2 H 4 ¥ 2 2 . 

Oxalate of allyle. Allylic alcohol. Oxamide. 

Allylene (C 3 H 4 ), the olefiant gas of the allyle series, is homologous with acetylene 
(C 2 H 2 ), and much resembles it in its chemical relations. It has been prepared by 
heating chlorinated propylene in a sealed tube with sodium-alcohol. The chlorin- 
ated propylene is a product of the action of pentachloride of phosphorus upon 
acetone — 

C 3 H 6 + PC1 5 = C 3 H 5 C1 + PCI3O + HC1; 

Acetone. Chlorinated 

propylene. 

C 3 H 5 C1 + C 2 H s FaO = C 3 H 4 + FaCl + C 2 H 6 . 

Sodium-alcohol. Allylene. Alcohol. 

By its action on ammoniacal nitrate of silver, it yields argentallylene, C 3 H 3 Ag. 
"When sodium is heated in allylene, carbon and hydrogen are liberated, and sodic 
acetylide is formed, C 3 H 4 + Na 2 = C 2 Na 2 + C + H 4 , a little propylene (C 3 H 6 ) is 
formed at the same time. 

345. Gum-resins. — The gum-resins consist of a mixture of gum with 
resin, and occasionally with essential oil, and are distinguished by their 
behaviour when triturated with water, which dissolves the gum and leaves 
the oil and resin suspended, giving the liquid a milky appearance. They 
also differ from most resins in being only partially soluble in alcohol. The 
gum-resins exude from the plants producing them in a milky state, 
gradually solidifying by exposure to the air. 

Asafoetida contains a resin of the composition C. 20 H 26 O 5 , and owes its 
powerful odour to an essential oil containing sulphur, which has been 
already noticed. Galbanum, ammoniacum, aloes, olibanum or frankincense, 
scammony, gamboge, myrrh, and euphorbium, also belong to the class of 
gum-resins. 

Caoutchouc (C 5 H 8 ) is so far allied to the gum-resins, that it is procured 
from a milky exudation furnished by several tropical plants, particularly 
by the Hcevcea guianensis and Jatropha elastica. Incisions are made in 
these trees, and the milky liquid thus obtained is spread upon a clay 
bottle-shaped mould, which is then suspended over a fire; a layer of 
caoutchouc is thus deposited upon the mould, and its thickness is after- 
wards increased by repeated applications of the milky liquid, the mould 
being eventually broken out of the caoutchouc bottle thus formed. The 
dark colour of the caoutchouc found in commerce is believed to be due 
to the smoke from the fire over which it is dried, for pure caoutchouc is 
white, and may be obtained in this state by dissolving in washed ether 



476 VULCANISED INDIA-RUBBER. 

and precipitating it by the addition of alcohol, in which it is insoluble. 
The caoutchouc of commerce contains a small quantity of albumen, derived 
from the original milky liquid, this being really a solution of albumen 
holding in suspension about 30 per cent, of caoutchouc, which rises to the 
surface like cream, when the juice is diluted with water and allowed to 
stand, becoming coherent and elastic when exposed to air. It will be 
remembered that many of the chief uses of caoutchouc depend upon its 
physical rather than its chemical properties, its lightness (sp. gr. 0*9 3) 
and impermeability to water adapting it for the fabrication of waterproof 
articles of clothing, of life-buoys, &c, whilst its remarkable elasticity gives 
rise to a still greater variety of applications. 

For the manufacture of waterproof cloth, caoutchouc is dissolved in 
rectified turpentine, and the solution is spread, in a viscid state, over the 
surfaces of two pieces of cloth of the same size, which are then laid face 
to face and passed between rollers, the pressure of which causes perfect 
adhesion between the two surfaces. Bisulphide of carbon, benzole, and 
coal naphtha, petroleum, the oils, both fixed and volatile, are also 
capable of dissolving caoutchouc. 

Marine glue is a solution of caoutchouc with a little shell-lac in coal 
tar naphtha. 

Waterproof felt is made by matting together fibres of cotton im- 
pregnated with a solution of caoutchouc in naphtha, and passing the felt 
between rollers. When kept for a length of time, its strength and water- 
proof qualities are deteriorated, in consequence of the oxidation of the 
caoutchouc, which is thus converted into a resinous substance resembling 
shell-lac, and easily dissolved by alcohol. 

The alkalies and diluted acids are without effect upon caoutchouc. 
When gently warmed, it becomes far more soft and pliable ; it fuses at 
about 250° F., and is converted into an oily liquid which becomes viscid 
on cooling, but will not again solidify, and is useful for lubricating stop- 
cocks. When further heated in air, it burns with a bright smoky flame. 
Heated in a retort, caoutchouc is decomposed into several hydrocarbons, 
one of which, called isoprene, boils at about 100° F., and has the com- 
position C 5 H 8 , while caoutchine has the same composition as oil of 
turpentine, and boils at .340° F. ; they are well adapted for dissolving 
caoutchouc. 

Vulcanised caoutchouc is produced by incorporating this substance with 
2 or 3 per cent, of sulphur, which not only increases in a remarkable 
manner its elasticity, but prevents it from cohering under pressure, and 
from adhering to other surfaces unless strongly heated. The vulcanised 
caoutchouc is also insoluble in turpentine and naphtha. Ordinary vul- 
canised caoutchouc generally contains more sulphur than is stated above, 
which causes it to become inelastic and brittle after it has been some 
time in use ; and for some purposes, such as the manufacture of overshoes, 
it is found advantageous to add some carbonate of lead as well as sulphur. 

When a sheet of caoutchouc is allowed to remain for some time in fused 
sulphur at 250° F, it absorbs 12 or 15 per cent, of that element without 
suffering any material alteration ; but if it be heated for a short time to 
300° F., it becomes vulcanised ; and when still further heated, is converted 
into the black horny substance called vulcanite or ebonite, and used for the 
manufacture of combs, &c. By treating the vulcanised caoutchouc w r ith 
sulphite of soda, the excess of sulphur above 2 or 3 per cent, may be dis- 
solved out. The whole of the sulphur may be removed, and the caout- 



GUTTA PERCHA. 477 

chouc devulcanised, by boiling it with a 10 per cent, solution of caustic 
soda. 

There are several processes employed for the manufacture of vulcanised 
caoutchouc; sometimes the sulphur is simply incorporated with it by 
mechanical means. Another process consists in immersing the caoutchouc 
in a mixture of 100 parts of bisulphide of carbon with 2 '5 parts of chloride 
of sulphur (fc^Cy,* or in dissolving the sulphur in oil of turpentine, which 
is afterwards used to dissolve the caoutchouc ; when the turpentine has 
evaporated, a mixture of caoutchouc and sulphur is left, which may easily 
be moulded into any desired form, and afterwards vulcanised by exposure 
to high pressure steam having a temperature of about 280° F. 

The true chemical constitution of vulcanised caoutchouc is not yet 
understood ; it has been suggested that the sulphur has been substituted 
for a portion of the hydrogen in the original caoutchouc, but it does not 
seem improbable that this hydrocarbon may combine directly with sulphur. 

Caoutchouc is by no means rare in the vegetable world, being found in 
the milky juices of the poppy (and thence in opium), of the lettuce, and 
of the euphorbium and asclepia families. 

Guttapercha, like caoutchouc, is originally a milky juice which exudes 
from, incisions made into the wood of the Isonandra perclia, a native of 
the Eastern archipelago. This juice soon solidifies when exposed to air, 
to a brownish mass heavier than caoutchouc (sp. gr. 0*98), and differing 
widely from it by being tough and inelastic at the ordinary temperature, 
becoming quite soft and plastic when heated nearly to the boiling point 
of water. Being impervious to water, it is employed as a waterproof 
material and for water-pipes, whilst its want of conducting power for 
electricity is turned to account in the coating of wires for the electric 
telegraph. 

Gutta percha is dissolved by the same substances which dissolve 
caoutchouc. It dissolves very slowly in ether, but is not affected by 
diluted acids and alkalies, and is employed for the manufacture of bottles 
in which hydrofluoric acid is kept. It liquefies at a moderately high 
temperature, and is afterwards decomposed, yielding products similar to 
those obtained from caoutchouc. 

The gutta percha of commerce appears to contain only about 80 per 
cent, of pure gutta percha (C 20 H 32 ), which is soluble in ether, the re- 
mainder consisting of two resins which may be dissolved out by boiling 
with alcohol, when a white crystalline resin (C 20 H 32 O 2 ) is deposited on 
cooling, leaving an amorphous resin (C 20 H 32 O) in solution. 

Pure gutta percha, exposed to air, is gradually converted into these 
resinous bodies, unless light be excluded. 

346. Gums. — Connected with the substances just described as being 
immediate products of vegetable life, are the gums, which, though resem- 
bling the resins in transparency and lustre, are at once distinguished from 
them by their solubility or softening in water, and by their insolubility in 
alcohol. 

Gum arable, which may be studied as the representative of this class, 
.is an exudation from certain species of acacia, and consists essentially of 
arabine, which has the composition C 12 H 22 O n . It dissolves readily, even 
in cold water, in large proportion, forming a viscid liquid, from which the 
arabine is precipitated in white flakes on adding alcohol. 

* A mixture of sulphur and chloride of lime is said to be sometimes employed. 



478 GUM — STARCH. 

When arabine is boiled with diluted sulphuric acid, it is converted slowly 
into grape-sugar (C 6 H 14 7 ) by assimilating the elements of water, a pro- 
perty connecting it closely with starch, which is susceptible of a similar 
conversion. 

But a chemical property distinguishing the gums is their behaviour 
with nitric acid, which furnishes mucic acid (H 2 C 6 H 8 8 ) and oxalic acid 
(H 2 C 2 4 ). The latter acid is also formed by the action of nitric acid upon 
starch and sugar, whilst mucic acid may be obtained by a similar process 
from sugar of milk and from manna sugar (mannite). 

Gum Senegal is often used in place of. gum arabic, especially by calico- 
printers to thicken their colours. It is darker in colour than gum arabic, 
but also consists essentially of arabine. 

Gum tragaeanth (C 12 H 20 O 10 ), which exudes from the Astragalus traga- 
cantha, is far less transparent than gum arabic, from which it also differs 
by not dissolving in water, but merely swelling up to a soft gelatinous 
mass. This variety of gum, which is also called mucilage, cerasine, or 
bassorine, is found, together with arabine, in the gum which exudes 
from the cherry, plum, almond, and apricot trees, and gives the mucila- 
ginous character to the watery decoctions prepared from certain seeds, such 
as linseed and quince-seed, and from the root of the marsh-mallow. 

Starch. 

347. Starch (C 6 H ]0 O 5 ) differs widely from the vegetable products just 
noticed, in being an indispensable constituent of certain parts of plants, 
in possessing an organised structure, and playing a very important part in 
the nutrition of the plant. 

In composition, it is seen to correspond with cellulose, which has also, 
it will be remembered, an organised structure ; but the function of cel- 
lulose in the plant appears to be chiefly, if not entirely, a mechanical one, 
since it forms the skeleton or framework of the plant, for which its resist- 
ance to chemical change especially adapts it ; whilst it will be seen that 
starch suffers chemical changes in the vegetable, which may be compared 
in some measure to the digestion of the food in the animal body. 

Starch is manufactured chiefly from potatoes, wheat, and rice. 

The solid portion of the potato consists chiefly of starch, as appears in 
the following result of analysis : — 

Composition of the Potato. 

Water, 75'9 

Vegetable albumen, 2*3 

Oily matter, 0'2 

Woody fibre, 0*4 

Starch, ....... 20'2 

Mineral substances, . . . . . l'O 

- 100-0 

In order to extract the starch, the potatoes are rasped to a pulp, which 
is washed upon a sieve, under a stream of water, as long as the latter is 
rendered milky by the starch suspended in it, the woody fibre being left* 
behind upon the sieve. The milky liquid is allowed to settle, and the 
clear water drawn off; the deposited starch is then stirred up with fresh 
water, and again allowed to subside, this process being repeated as long 
as the water is coloured, after which the starch is mixed with a small 



MANUFACTURE OF STARCH. 479 

quantity of water, and passed through a fine sieve to separate mechani- 
cally mixed impurities ; it is finally drained and dried, first, in a current 
of air, and afterwards by a gentle heat. 

Starch cannot be extracted from wheat so easily as from potatoes, on 
account of the much larger proportion of other solid matters from which 
■it must be separated. 

Composition of Wheat. 



Water, 

Vegetable albumen, 

Oily matter, 

Woody fibre, 

Starch, 

Dextrine and sugar/ 

Gluten, 

Mineral substances, 



12-1 

2-0 

1-1 

1-5 

60'8 

10-5 

10-5 

1-5 

ioo-o 



To extract the starch, the coarsely-ground wheat is moistened with 
water, and allowed to putrefy, as it easily does, in consequence of the alter- 
able character of the gluten (which contains carbon, hydrogen, nitrogen, 
oxygen, and sulphur) \ the putrefying gluten excites fermentation in the 
sugar and part of the starch, producing acetic and lactic acids. These 
acids are capable of dissolving the remainder of the gluten, which may 
then be washed away by water, the subsequent processes being similar to 
those employed in the extraction of potato starch. 

A far more economical and scientific method of extracting the starch 
consists in dissolving the gluten by means of a weak alkaline solution, 
which leaves the starch untouched. This process is especially applied in 
the manufacture of starch from rice, the composition of which is here 
given : — 

Composition of Rice. 

Water, 5*0 

Starch, . . . . . . . 83*0 

Gluten, 6*0 

Woody fibre, 4 '8 

Sugar, ) - VQ 

Dextrine, ) 

Oily matter, ...... "1 

Mineral matters, . . . . . '1 



ioo-o 



The whole rice is allowed to soak for twenty-four hours in water con- 
taining ^ £ o-th of its weight of caustic soda ; it is then washed and ground 
into flour, which is again soaked for two or three days in a fresh alkaline 
solution ; the starch is allowed to settle, and the alkaline liquor holding 
the gluten in solution is drawn off. To complete the purification of the 
starch, it is stirred up with water, the heavier woody fibre allowed to sub- 
side, and the milky liquid is run off into another vessel, where it deposits 
the starch. 

Starch is usually sent into commerce in the rough prismatic fragments 
into which it splits during the process of drying, and is generally coloured 
blue by the addition of a little artificial ultramarine or smalt, in order to 
correct the yellow tint of linen. Commercial starch generally contains 
about 18 per cent, of water. 

* The existence of sugar in wheat is denied by Peligot. 



480 



PROPERTIES OF STARCH. 



Starch being possessed of an organised structure, might be expected to 
vary in external characters with the source from which it was derived ; 
and, accordingly, we find that, with the help of the microscope, it may be 
ascertained from what plant any particular specimen of starch was pro- 
cured, a result which could not be arrived at by a chemical examination. 

Thus, powdered starch from the potato (P, fig. 288) appears under the 
microscope in very irregular ovoid granules, marked with concentric rings, 
and of larger size than those from most other vegetables, the long diameter 




Fig. 288. 



of the grains being usually about -^i-g- inch. Wheat starch (W) exhibits 
grains which are nearly circular, and are not marked with rings ; they are 
much smaller than those of potato starch, having a diameter of about 
roVo °f an incn « The grains of rice starch (R) are angular, and still 
smaller, measuring only about 5-^5-3- of an inch in diameter. A represents 
the starch granules of arrow-root. 

Starch is quite unaffected by cold water ; but if it be heated with water 
to a temperature above 140° F., the granules swell up, burst, and yield 
the well-known viscid liquid used by laundresses. If this be mixed with 
a large quantity of water, and allowed to stand, some of the imperfectly 
burst granules subside, but the greater part of the starch remains so inti- 
mately mixed with the water, that it is not separated by filtration through 
paper, though it has been shown that when the rootlets of a hyacinth are 
immersed in the diluted magma of starch, the water alone is taken up by 
the capillary vessels, affording a strong presumption that the starch was 
simply in a state of suspension in the water. If the boiled starch be eva- 
porated to dryness, a brittle mass remains, which may again be taken up 
without difficulty by water. 

This peculiar behaviour of starch with water is closely connected with 
its use as food. Raw starch is digested with difficulty, and often passes 
unaltered through the bowels ; but the ease with which the starch gela- 
tinised by heat is digested, is shown by the wholesomeness of sago, 
tapioca, and arrow-root, which consist simply of starch, and are prepared 
for food by heating them with water to the point at which the granules 
burst. 

Arrow-root is the starch extracted from the root of the Maranta arum 
dinacea, and of some other tropical plants. 

In the preparation of tapioca and sago, the starch is dried at a tem- 
perature above 140° F., so that it loses its ordinary farinaceous appearance 
and becomes semi-transparent. 

Sago is manufactured from the pith of certain species of palm, natives 
of the East Indian islands. The tree is split so as to expose the pith, 
which is mixed with water, and the starch having been separated from 
the woody fibre in the usual manner, is pressed through a perforated 
metallic plate, which moulds it into small cylinders ; these are placed in a 



CONVERSION OF STARCH INTO DEXTRINE. 481 

revolving vessel and broken into rough spherical grains, which are steamed 
upon a sieve, and dried. 

Tapioca is obtained from the roots of the Jatropha manihot, a native 
of America. The roots are peeled and subjected to pressure, which 
squeezes out a juice employed by the Indians to poison their arrows, and 
containing a deleterious substance which has been named jatrophine. 
When the juice is allowed to stand, it deposits starch, which is well 
washed, pressed through a colander, and dried at 212° F. 

Oswego, or corn-flour, is the flour of Indian corn deprived of gluten by 
treatment with a weak solution of soda. 

348. Dextrine. — When starch is heated in an oven to about 400° F. 
for an hour or two, it becomes easily soluble in cold water, yielding a 
solution having all the properties of gum ; the starch has indeed been 
converted into a new substance known as dextrine or British gum, which 
is largely used by calico-printers for thickening their colours, and is sub- 
stituted for ordinary gum in many other applications. There is a current 
anecdote which attributes the discovery of dextrine to a conflagration at 
a starch-factory, where the work-people, who assisted in quenching the 
fire, observed the gummy properties of the water which had been thrown 
over the torrefied starch. In toasting bread, a portion of the starch is 
converted into dextrine, which is dissolved by the water in the prepara- 
tion of toast and water. Farinaceous foods for infants are made by baking 
flour, in order to convert the starch into dextrine. 

It is very remarkable that the composition of dextrine (C 6 H 10 O 5 ) is 
precisely that of starch ; they are isomeric bodies, so that the difference in 
their properties must be ascribed to a. difference in the arrangement of 
their component particles ; the name of dextrine was conferred upon this 
gummy substance on account of the power possessed by its solution of 
causing a right-handed rotation in a ray of polarised light. When oxidised 
by nitric acid, dextrine, like starch, is converted into oxalic acid, a cir- 
cumstance distinguishing it from ordinary gum, which furnishes mucic 
acid when acted upon by nitric acid. 

Dextrine is usually prepared on the large scale Jby moistening 10 parts 
of starch with 3 parts of water acidulated with T^th of nitric acid ; the 
mixture is allowed to dry, and spread upon trays in an oven, where it is 
heated for an hour or so to 240° F. The nitric acid thus allows the 
starch to be converted into dextrine at a temperature which would be 
quite inadequate to effect the transformation of starch alone. 

This power of accelerating the conversion of starch into dextrine is 
shared by all acids. Hence if starch be boiled with water, and the viscid 
liquid so obtained be mixed with an acid, and again boiled, it gradually 
becomes thinner, and is eventually converted into dextrine. The change 
is very readily effected by boiling the starch solution with a few drops of 
sulphuric acid, and the gradual conversion of the starch may be traced by 
means of an aqueous solution of iodine. On adding this solution to a por- 
tion of the (cold) solution of starch, it produces the usual dark blue 
colour ; but on adding it, at intervals, to portions of the acidulated and 
boiled liquid, taken away and cooled for the purpose, the blue colour will 
be replaced by a peculiar vinous purple tint which iodine imparts to solu- 
tions of dextrine containing a little unchanged starch. 

The solution of iodine is much used in proximate organic analysis as a 
test for starch, and it is necessary to bear in mind that the blue colour is 

2 H 



482 GERMINATION OF SEEDS. 

bleached by alkalies (which take up the iodine) and by heat, though, in 
the latter case, it may be restored by cooling the liquid. The blue colour 
does not appear to be due to the formation of any definite chemical com- 
pound with the starch, but rather to a mechanical adhesion of very finely 
divided iodine to the particles of starch. The sensitiveness of starch to 
the action oifree iodine has given rise to its application in the preparation 
of paper for the prevention of forgery in bankers' cheques, &c. If paper 
be impregnated with a mixture of iodide of potassium and starch, which 
is perfectly white, it will acquire an intense blue colour on the application 
of any of the bleaching ageuts (chlorine, hypochlorous acid, chlorides of 
lime and soda), generally used for removing ink, as these liberate the 
iodine, which immediately blues the starch. 

If the ebullition of the dextrine in contact with the sulphuric acid be 
continued, the solution entirely loses its property of being coloured by 
iodine, and acquires a sweet taste, the dextrine having been converted into 
glucose or grape-sugar (C 6 H u 7 ) by assimilating the elements of two 
molecules of water* — 

C 6 H 10 O 5 (Dextrine) + 2H 2 = C 6 H 14 7 (Grape-sugar) . 

349. Germination of seeds — Malting. — This tendency of starch to com- 
bine with the elements of water and pass into grape-sugar, will be found 
of immense importance in the chemistry of vegetation, as well as in that of 
food. It is, indeed, the chief chemical change concerned in the develop- 
ment of living from inanimate matter, being one of the first processes 
involved in the germination of a seed — the first step in the production of 
vegetables, which must precede the animals whose food they compose. 

The components of all seeds are similar to those of wheat, which have 
been enumerated above ; and if they be perfectly dried immediately after 
their removal from the parent plant, they may be preserved for a great 
length of time unchanged, and without losing the power of germinating 
under favourable circumstances. The essential conditions of germination 
are the presence of air and moisture, and a eertain temperature, which varies 
with the nature of the seed. These conditions being fulfilled, the seed ab- 
sorbs oxygen from the air, and evolves carbonic acid, produced by the com- 
bination of the oxygen with the carbon of one or more of the most alter- 
able constituents of the seed, such as the vegetable albumen or the gluten. 
This process of oxidation is attended with evolution of heat, which serves 
to maintain the seed at the degree of warmth most favourable to germina- 
tion. The component particles of the albumen or gluten having been set 
in motion by the action of the atmospheric oxygen, induce a movement or 
chemical change in the starch with which they are in contact, causing it 
to pass into dextrine and grape-sugar, which, unlike the starch, being 
perfectly soluble in water, are capable of affording to the developing shoot, 
the carbon, hydrogen, and oxygen which it requires for the increase of its 
frame. The production of grape-sugar and of dextrine in germination is 
well illustrated by the sweet gummy character of the bread made from 
sprouted wheat, and is turned to practical account in the process of 
malting. 

* There is some reason to believe that the formation of grape-sugar from starch results 
from a change similar to that by which it is obtained from salicine and. other glucosides. 
Thus— 

C la H 80 O 10 + 2H,0 = C 6 H 10 O 3 + C H 14 O 7 . 
2 mol. starch. Dextrine. Glucose. 



PROCESS OF MALTING. 433 

During the germination of all seeds there is formed, apparently by the 
oxidation of one of the more alterable constituents, a peculiar substance 
containing carbon, hydrogen, nitrogen, and oxygen, which has never yet 
been obtained from any other source, and is characterised by its remark- 
able property of inducing the conversion of starch into dextrine and grape- 
sugar. 

This substance has been termed diastase (Stao-rao-is, dissension; metaph. 
fermentation), but has never yet been obtained in a state of sufficient 
purity to enable its formula to be satisfactorily determined. It may be 
extracted, however, from malt, by grinding it, and mixing it with half 
its weight of warm water, which dissolves the diastase ; the solution 
squeezed out of the malt is heated to about 170° F., filtered from any 
coagulated albumen, and mixed with absolute alcohol, which precipitates 
the diastase in white flakes. One part of diastase dissolved in water is 
capable of inducing the conversion of 2000 parts of starch into dextrine 
and grape-sugar, the diastase itself being exhausted in the process. A 
temperature of about 150° F. is most favourable to the action of diastase, 
which may be arrested entirely by raising the liquid to the boiling 
point. 

The great importance of diastase in the arts of the brewer and distiller 
is at once apparent. In the process of malting barley, the grain is soaked 
in water, and afterwards spread out in thin layers upon the floor of a dark 
room (thus imitating the natural condition under which the seed germi- 
nates), which is maintained as nearly as possible at a constant and moderate 
temperature (between 55° and 62° F.) ; spring and autumn are, therefore, 
more favourable to malting than summer and winter. It soon evolves 
heat, and the grains begin to swell; in the course of twenty-four hours 
the germination commences, and the radicle makes its first appearance as 
a whitish protuberance ; the grain is turned two or three times a-day, in 
order to equalise the temperature. In about a fortnight, the radicle has 
grown to about half an inch, by which time a sufficient quantity of dias- 
tase has been formed. In order to prevent the germination from proceed- 
ing further, the grain is killed by drying it at a temperature of 90° F. on 
perforated metallic plates, where it is afterwards, heated to about 140° F., 
so as to render it brittle, after which it is sifted in order to separate the 
radicle, which is now easily broken off. This radicle is found to contain 
as much as Jth of the total quantity of the nitrogen present in the barley, 
so that the malt dust, as the sittings are called, forms a valuable 
manure. 

100 parts of barley generally yield about 80 parts of malt, but a part of 
the loss is due to water present in the barley, so that 100 parts of dry 
barley yield 90 parts of malt, and 4 parts of malt dust, the difference, viz., 
6 parts, representing the weight of the carbon converted into carbonic acid, 
of the hydrogen (if any) converted into water during the germination, and 
of soluble matters removed from the barley in steeping. Malt contains 
about -g-g-o-th of its weight of diastase, far more than enough to ensure the 
conversion of the whole of its starch into sugar. 

The following table* illustrates the change in composition suffered by barley 
during the process of malting, leaving the moisture out of consideration : — 

* Lawes ; Report on the Relative Values of Unmalted and Malted Barley as Food for 
Stock. 1866. 



484 



CHEMISTRY OF BREWING-. 





Barley. 


After 

Steeping. 


14£ days 
on floor. 


Malt after 
Sifting. 


Malt Dust. 


Sugar, 

Starch, . . . ) 
Dextrine, . . . i 
"Woody fibre, . . . 
Albuminous matter, 
Mineral matter, . . 


2'56 

80-42 

4-69 
9-83 
2-50 


1-56 

81-12 

5-22 
9-83 

2-27 • 


12-14 

70-09 

5-03 

10-39 

2-35 


11-01 

72-03 

4-84 
9-95 
2-17 


11-35 

43-68 

9-67 

26-90 

8-40 


100-00 


100-00 


100-00 


100-00 


100-00 



350. Br etving. — In order to prepare beer, the brewer mashes the 
ground malt with water at about 180° F. for some hours, when the dias- 
tase induces the conversion, into dextrine and sugar, of the greater part 
of the starch which has not been so changed during the germination, and 
the wort is ready to be drawn off for conversion into beer. The undis- 
solved portion of the malt, or brewers' grains, still contains a considerable 
quantity of nitrogenised matter, and is employed for feeding pigs. 

That malt contains far more diastase than is necessary to convert its 
starch into sugar, is shown by adding a little infusion of malt to the 
viscid solution of starch, and maintaining it at about 150° F. for a few 
hours, when the mixture will have become far more fluid, and will no 
longer be coloured blue by solution of iodine. In distilleries, advantage 
is taken of the excess of diastase in malt, by adding 3 or 4 parts of 
unmalted grain to it, when the whole of the starch in this latter is also 
converted into dextrine and sugar, and the labour and expense of malting 
it are avoided. 

The wort obtained by infusing malt in water contains not only grape- 
sugar, dextrine, and diastase, but a considerable quantity of nitrogenised 
matter formed from the gluten (or albuminous matter) of the barley. Before 
subjecting it to fermentation, it is boiled with a quantity of hops, usually 
amounting to about ^th of the weight of the malt employed, which is 
found to prevent, in great measure, the tendency of the beer to become 
sour in consequence of the conversion of the alcohol into acetic acid. 

The hop contains about 10 per cent, of an aromatic yellow powder, 
called lupuline, which appears to be the active portion, and which con- 
tains a volatile oil of peculiar odour, together with a very bitter sub- 
stance. 

The hopped wort is run off into a vat, where it is allowed to deposit 
the undissolved portion of the hops, and the clear liquor is drawn off 
into shallow coolers, where its temperature is lowered as rapidly as possi- 
ble to about 60° F., the cooling being usually hastened by cold water 
circulating through pipes which traverse the coolers. If the wort be 
cooled too slowly, the nitrogenised matter which it contains undergoes 
an alteration by the action of the air, in consequence of which the beer 
is very liable to become acid. 

The wort is now transferred to the fermenting tun, where it is made 
to ferment by the addition of yeast, usually in the proportion of y-^th 
of its volume. 

Yeast is a minute fungoid vegetable, which grows in solutions 



YEAST — FERMENTATION. 485 

containing sugar together with, some nitrogenised substance (e.g., a salt of 
ammonia), and the salts (phosphates of potash, soda, lime, and magnesia), 
which are essential constituents of its cells. It is only recently that the 
conditions under which the yeast plant grows have been ascertained, 
and the seeds or germs from which it originates have hitherto eluded 
detection, though it may be remarked that in this respect it only 
resembles some of the lower mosses, the vegetable character of which has 
never been called in question. 

If a little white of egg, cheese, or a piece of flesh (all of which con- 
tain carbon, hydrogen, nitrogen, oxygen, and phosphates), be placed in a 
solution of sugar, and allowed to undergo decomposition, a grey scum 
forms upon the liquid, which is seen under the microscope to consist of 
irregularly oval cells, the growth of which may be watched under the 
microscope in a little of the liquid from which they were obtained, when 
they will be found to multiply rapidly by the production of new cells on 
all sides of them (fig. 289). The same cells will be developed very 
rapidly in the sweet wort of malt, allowed to 
undergo decomposition between 60° and 70° F. 

These cells contain a substance somewhat 
resembling albumen, enclosed in a thin mem- 
brane, the composition of which is similar to 
that of cellulose. They also contain a peculiar 
nitrogenised body resembling diastase, and 
capable of inducing the conversion of cane- 
sugar (C 12 H 22 O n ) into grape-sugar (C 6 H 14 7 ). 
Accordingly, when yeast is added to a solution 
of cane-sugar, the liquid is found to increase 
in specific gravity (a solution of cane-sugar 
having a lower density than one containing an 
equivalent quantity of grape-sugar), previously Fig 289. 

to the commencement of fermentation, and 

the application of tests readily proves the presence of grape-sugar in 
the solution. 

The grape-sugar then undergoes the decomposition known as alcoholic 
fermentation, which results in the production of alcohol, carbonic acid, 
lactic acid, succinic acid, glycerine, and a peculiar brown soluble matter, 
together with other substances, the true nature of which is yet undeter- 
mined. The fermentation is attended with a considerable elevation of 
temperature. 

Taking into consideration only the alcohol and carbonic acid, which 
are the chief products, their formation from grape-sugar may be repre- 
sented by the equation — 

C 6 H 14 7 = 2C 2 H 6 + 2C0 2 + H 2 . 

Grape-sugar. Alcohol. 

During the fermentation the yeast cells are gradually broken up, so 
that a given quantity of yeast is capable of fermenting only a limited 
quantity of sugar. On an average, a quantity of yeast containing between 
two and three parts of solid matter is required to complete the fermenta- 
tion of 100 parts of sugar. The solution remaining after the fermenta- 
tion is found to contain salts of ammonia, which have been formed at the 
expense of the nitrogen of the yeast. 

If the liquid in which the yeast excites fermentation contain nitro- 




486 



COMPOSITION OF BEER. 



genised matters and phosphates, the yeast plant grows, and its quantity- 
increases ; thus in the sweet wort from malt, the yeast is nourished by 
the altered gluten and by the phosphates, so that it increases to six 
or eight times its original weight. 

If yeast be heated to the boiling point of water, the plant is killed, as 
might be expected, and loses its power of inducing alcoholic fermentation ; 
but it may be dried at a low temperature, or by pressure, without losing 
its fermenting power, and dried yeast is an article of commerce. German 
dried yeast is produced in the fermentation of rye for making Hollands. 

Yeast will not cause fermentation in a solution containing more than 
one-fourth of its weight of sugar, and the fermentation is arrested when 
the alcohol amounts to one-fifth of the weight of the liquid, so that the 
strength of fermented liquors could never exceed 20 per cent, of alcohol. 
The fermentation is also arrested by the mineral acids, and by many of 
the substances to w T hich antiseptic properties are commonly attributed, 
such as common salt, kreasote, corrosive sublimate, sulphurous acid, tur- 
pentine, &c. 

In the fermentation of beer, the yeast is carried up to the surface by 
the effervescence due to the escape of the carbonic acid, and is eventually 
removed, in order to be employed for the fermentation of fresh quantities 
of wort. 

When the fermentation has proceeded to the required extent, the beer 
is stored for consumption. 

It will be seen that the chief constituents of beer are th 
nitrogenised substance derived from the albuminous matter of the barley, 
and not consumed in the growth of the yeast, the unaltered sugar and 
dextrine, the brown or yellow colouring matter formed during the fer- 
mentation, the essential oil and bitter principle of the hop. 

Beer also contains acetic acid (formed by the oxidation of the alcohol, 
p. 487), free carbonic acid, which gives its sparkling character, together 
with the lactic and succinic acids and glycerine, formed as secondary pro- 
ducts of the fermentation, and ammoniacal salts derived from the yeast. 
The soluble mineral substances from the barley are also present, minus 
the phosphates abstracted by the yeast. 

The proportions of the constituents, of course, vary greatly, as will be 
seen from the following examples : — 



alcohol, the 



Percentage of 


Allsopp's 
Ale. 


Bass's Ale. 


Strong Ale. 


Whitbread's 
Porter. 


Whitbread's 
Stout. 


Alcohol, . . • . . 

Acetic acid, .... 

Sugar and other solid ) 

matters, . . . \ 


6-00 
0-20 

5-00 


7-00 

0'18 
4-80 


8-65 
0*12 

6-60 


4*20 
0-19 

5-40 


6-00 
0-18 

6-38 



The dark colour of porter and stout is caused -by the addition of a 
quantity of high-dried malt which has been exposed to so high a tempera- 
ture in the kiln as to convert a portion of its sugar into a dark brown 
soluble substance called caramel. It is said that alum and sulphate of 
iron are also added to porter and stout to cause them to froth strongly. 
The peculiar aroma of beer is probably due to the presence of a minute 
quantity of some fragrant ether, produced during the fermentation. 

In some cases, when the operation of brewing has been badly con- 



9 

MANUFACTURE OF VINEGAR. 487 

ducted, the beer becomes ropy, or undergoes the viscous fermentation. In 
this case the sugar suffers a peculiar transformation, resulting in the pro- 
duction of a mucilaginous substance resembling gum in its composition. 
This change may be induced in sugar by yeast which has been boiled, or 
by water in which flour or rice has been steeped. White wine occa- 
sionally becomes ropy from a similar cause, but red wines are not liable to 
this change, apparently because the tannin which they contain has preci- 
pitated in an insoluble form the ferment which induces it. During this 
viscous fermentation a part of the sugar is often converted into mannite 

351. Acetifjcation — Manufacture of Vinegar. — Beer which has 
become sour is often said to have undergone the acetous fermentation ; 
but this is not strictly correct, the change being more similar to decay, 
since it is one in which the oxygen of the air directly takes part. The 
acidity of sour beer is caused by the acetic acid (C 2 H 4 2 ) formed by the 
action of atmospheric oxygen upon the alcohol, according to the equation — 

C 2 H 6 {Alcohol) + 2 = C 2 H 4 2 (Acetic Acid) + H 2 . 

Pure alcohol may be exposed to the air, either alone or when mixed with 
water, for any period, without suffering oxidation ; but when in contact 
with certain changeable organic substances, the alcohol undergoes oxida- 
tion, and is converted into acetic acid. It is upon this circumstance that 
the different methods of producing vinegar are based. 

The most direct application of this principle is made in the so-called 
quick vinegar process in use in continental countries where alcohol is 
free of duty. Alcohol of about 80 per cent, is mixed with 6 parts of 
water, and with about T oVo^ n P art 
of yeast, or some other alterable sub- 
stance containing nitrogen. This mix- 
ture is heated to about 80° F., and 
caused to trickle slowly from pieces of 
cord fixed in a perforated shelf over a 
quantity of wood shavings* previously 
soaked in vinegar, which is found 
materially to assist the acetification, 
and packed in a tall cask (fig. 290), 
in which holes have been drilled in 
order to allow the entrance of air. The 
oxidation of the alcohol soon raises the 
temperature to about 100° F., which 
occasions a free circulation of air -pi*. 290. 

among the shavings. The mixture is 

passed three or four times through the cask, and in about 36 hours the 
conversion into vinegar is completed. The oxidation of the alcohol in 
this process is found to be arrested by the presence of essential oils, or of 
kreasote, and similar antiseptic substances. 

The necessity of affording a full supply of atmospheric air was not 
appreciated until Liebig had proved the existence of an intermediate stage 
in the process, consisting in a partial oxidation of the alcohol by which 
it became converted into aldehyde (C 2 H 4 0), an extremely volatile liquid 

* These shavings appear to favour the process by serving as points of attachment for a 
microscopic vegetable, which encourages the oxidation of the alcohol. 




488 GLUTEN — VEGETABLE FIBRIN E. 

(boiling at 70° ¥.), which was lost in the form of vapour, thus greatly 
diminishing the proportion of vinegar obtained — 

C 2 H 6 (Alcohol) + = C 2 H 4 (Aldehyde) + H 2 . 

If a sufficient quantity of atmospheric air be supplied, the production of 
aldehyde is entirely avoided. 

White wine vinegar is prepared in France from light wines by a process 
of much longer duration. A little boiling vinegar is poured into a cask, 
partially open at the top, together with four or five gallons of white wine 
which has been allowed to trickle over wood shavings. In a few days, 
during which the temperature is maintained at about 80° F., a fresh quan- 
tity of wine is poured in, and in the course of a fortnight half the vinegar 
contained in the cask is drawn off, and replaced by a fresh portion of wine. 
In this way an occasional renewal of the air in the upper part of the cask 
is provided for. The acetification is found to proceed more rapidly in old 
casks than in new ones, which is attributed to the presence of a peculiar 
conferva deposited upon the sides of the former, and styled mother of 
vinegar. It is probably for a similar reason that the acetification is pro- 
moted by the addition of ready-made vinegar at the commencement of the 
process. 

In this country vinegar is chiefly prepared from malt, the infusion of 
which is allowed to undergo the alcoholic and acetous fermentation. 

Vinegar contains on an average about 5 per cent, of acetic acid, together 
with small quantities of vegetable and mineral substances, varying with 
the source from which it was obtained. Its pleasant aroma is due to the 
presence of some acetic ether (C 2 H 5 .C 2 H 3 2 ) formed during its manu- 
facture. The vinegar of commerce is allowed to be mixed with xoVo-th 
of its weight of sulphuric acid in order to prevent it from becoming 
mouldy. 

Bread. 

352. The chemistry of fermentation is intimately connected with the ordi- 
nary process of bread-making. It will be remembered that wheaten flour 
(p. 479) consists, essentially, of starch and gluten, with a little dextrine 
and sugar. On mixing the flour with a little water, it yields a dough, the 
tenacity of which is due to' the gluten present in the flour. If this dough 
be tied up in a piece of fine muslin, and kneaded under a stream of water, 
the starch will be suspended in the water, and will pass through the 
muslin, whilst the gluten will remain as a very tough elastic mass, which 
speedily putrefies if exposed to the air in a moist state, and dries up to a 
brittle horny mass at the temperature of boiling water. 

On analysis, gluten is found to contain carbon, hydrogen, nitrogen, and 
oxygen, in proportions which may be represented by the empirical formula 
C 24 H 40 N 6 O 7 , though it cannot be regarded as a single independent sub- 
stance, but as a mixture of three substances very closely allied in compo- 
sition. 

When gluten is boiled with alcohol, one portion refuses to dissolve, and 
has been named vegetable fibrine, from its resemblance to the substance 
forming the muscles of animals. When the solution in alcohol is allowed 
to cool, it deposits a white flocculent matter, very similar to the caseine 
which composes the curd of milk. On adding water to the cold alcoholic 
solution, a third substance (glutine) is separated, which much resembles 
the albumen found so abundantly in the blood. 



PROCESS OF BREAD-MAKING. 489 

The presence in gluten of three substances, similar to the three principal 
components of the animal body, leads us to form a high opinion of its 
value as a nutritive compound. But gluten itself, separated from the flour 
by the process above described, would be found very difficult of digestion, 
on account of its resistance to the solvent action of the fluids in the 
stomach ; indeed, the dough composed of flour and water is proverbially 
indigestible, even when baked. In order to render it fit for food, it must 
be rendered spongy or porous, so as to expose a larger surface to the action 
of the digestive fluids of the body ; the most direct method of effecting 
this is the one adopted in the manufacture of the aerated bread, and con- 
sists in mixing the flour with water which has been highly charged, under 
pressure, with carbonic acid gas ; the mixing having been effected in a 
strong closed iron vessel, an aperture in the lower part of this is opened, 
when the pressure of the accumulated gas forces the dough out into the 
air, and the gas which had been imprisoned in the dough expands, con- 
ferring great porosity and sponginess upon the mass in its attempt to 
escape. In another process for preparing unfermented bread, the flour is 
mixed with a little bi-carbonate of soda, and is then made into a dough 
with water acidulated with hydrochloric acid ; the latter decomposing 
the bi-carbonate of soda, liberates its carbonic acid, which renders the 
bread porous. The chloride of sodium formed at the same time remains 
in the bread. In the preparation of cakes and pastry, the same object is 
sometimes attained by adding carbonate of ammonia to the dough ; when 
heat is applied, in the baking, the salt is converted into vapour which 
distends the dough. 

In the common process of bread-making, however, the carbonic acid 
destined to confer sponginess upon the dough is evolved by the fermenta- 
tion of the sugar contained in the flour ; the latter having been kneaded 
with the proper proportion (usually about half its weight) of water, a little 
yeast and salt are added, and the mixture is allowed to stand at a tempera- 
ture of about 70° F. for some hours. The dough swells or rises considerably 
in consequence of the escape of carbonic acid, the sugar being decomposed 
into that gas and alcohol, as in ordinary fermentation. The spongy dough 
is then baked in an oven, heated to about 500° I\, when a portion of the 
water and the whole of the alcohol are expelled, the carbonic acid being 
also much expanded by the heat, and the porosity of the bread increased. 
The granules of starch are much altered by the heat, and become far more 
digestible. Although the temperature of the inside of the loaf does not 
exceed. 212° F. the outer portion becomes dry and hard, the hottest part 
being even torrefied or scorched into crust. 

Occasionally, instead of yeast, leaven is employed, in order to ferment 
the sugar, leaven being dough which has been left in a warm place until 
decomposition has commenced. 

The passage of new into stale bread does not depend, as was formerly 
supposed, upon the drying of the bread consequent upon its exposure to 
air, but is a true molecular transformation which takes place equally well 
in an air-tight vessel, and without any loss of weight. It is well known 
that when a thick slice of stale bread is toasted, which dries it still 
further, the crumb again becomes soft and spongy as in new bread ; and 
if a stale loaf be again placed in the oven, it is entirely reconverted into 
new bread. 

Wheaten flour is particularly well fitted for the preparation of bread on 
account of the great tenacity of its gluten. Next to wheat in this respect 



490 PRODUCTION OF GRAPE-SUGAR FROM STARCH. 

stands rye, whilst the other cereals contain a gluten so deficient in tena- 
city that it is impossible to convert them into good bread. 

Barley bread is close and heavy, since its nitrogenised matter is chiefly 
present in the form of albumen, which does not vesiculate like gluten, 
during the fermentation. 

Even in wheaten flour the tenacity of the gluten is liable to variation, 
and in order to obtain good bread from a flour the gluten of which is 
inferior in this respect, it is customary to employ a minute proportion of 
alum. This addition being considered unwholesome by some persons, it 
would be better to substitute lime-water, which has been found by Liebig 
to have a similar effect. Sulphate of copper improves in a very striking 
manner the quality of the bread prepared from inferior flour, but this 
salt is far more objectionable than alum. 

The Sugars. 

353. The conversion of starch into grape-sugar, when heated in contact 
with diluted acids (p. 482), is taken advantage of for the preparation of 
this variety of sugar on the large scale. For this purpose, water acidulated 
with T -g-g-tn of sulphuric acid is heated to ebullition, and a hot mixture of 
starch and water allowed to flow gradually into it, so as not to reduce its 
temperature below the boiling point. The mixture is kept boiling for 
half-an-hour, after which chalk is added in small portions at a time to 
neutralise the sulphuric acid, and the sulphate of lime having been 
allowed to subside, the clear syrup is drawn off, and evaporated to the 
crystallising point. The conversion is accelerated by heating under 
pressure with steam at 320° E. 

The grape-sugar or glucose thus manufactured cannot be employed as a 
substitute for the sugar extracted from the sugar-cane, on account of its 
greatly inferior sweetening power, which is less than half that possessed 
by cane-sugar.* It is, moreover, far less soluble in water, 1 part of grape- 
sugar requiring 1-J part of water to dissolve it, whilst cane-sugar requires 
only J part. Grape-sugar has been employed, however, for the adultera- 
tion of cane-sugar and honey. The fraud is easily detected in cane-sugar 
by boiling a portion of the sample with a little solution of potash, when 
the grape-sugar is decomposed, and colours the liquid intensely brown, 
pure cane-sugar giving very little brown colour unless boiled for a long 
time. A more delicate mode of detection consists in adding to a solution 
of the sugar a few drops of solution of sulphate of copper, and enough 
solution of potash to form an intensely blue liquid. The oxide of copper 
is not precipitated in the presence of either of the sugars ; but if the blue 
liquid be very gently heated, a red precipitate of suboxide of copper will 
separate if grape-sugar be present, whilst with pure cane-sugar the pre- 
cipitation does not take place unless the solution is boiled. Sulphate of 
lime will generally be detected in sugar or honey adulterated with glucose. 

Even cellulose is transformed into dextrine and grape-sugar under the 
influence of sulphuric acid. If linen, calico, cotton-wool, or paper be 
dried, and gradually moistened with 1J part of concentrated sulphuric 
acid, avoiding elevation of temperature, it is converted in the course of a 
few hours into a gummy mass which dissolves in water, and is very 
similar to dextrine. "When the cellulose has been left in contact with 

* Hence the loss of sugar by sweetening tarts before baking them, part of the sugar 
being converted into grape-sugar by the vegetable acids of the fruit. 



SUGAR OF FRUITS. 491 

the acid for a day or two, it should be dissolved in a large quantity of 
water, and boiled for 8 or 10 hours in order to effect the conversion into 
sugar : the acid may then be neutralised with chalk, the solution filtered 
from the sulphate of lime, and evaporated, when it furnishes a crystalline 
mass of grape-sugar. 

Closely connected with the conversion of cellulose into dextrine by 
contact with strong sulphuric acid, is that very remarkable change of 
paper into vegetable parchment. If dry white blotting-paper be drawn 
through a cooled mixture of the strongest oil of vitriol with half its bulk 
of water, and be then thoroughly washed in a large volume of water, it 
becomes five times as strong as before, and has f ths of the strength of 
ordinary animal parchment. The parchment paper, when dry, is found 
to have suffered no alteration in weight, and analysis shows its composi- 
tion to be unchanged. This remarkable increase in strength must, there- 
fore, be referred to a molecular alteration. The paper is also found to 
have become almost waterproof, and presents a somewhat translucent 
appearance like paper which has been slightly oiled. It receives many 
useful applications, for luggage labels which are not easily torn or re- 
moved by rain, and as a substitute for animal membrane in tying over 
preserves, &c. 

This susceptibility of conversion into grape-sugar possessed by starch 
and cellulose, affords a very important clue in tracing the changes which 
take place in living vegetables. It has been already seen (p. 482) that 
during the germination of seeds, their starch is converted into sugar, in 
order that it may be carried in a soluble form to the extending limbs 
of the vegetable frame ; but it would appear that in these parts, where 
a deposition of cellulose is required, the sugar (C 6 H 14 7 ) is reconverted 
into that substance (C 6 H 10 O 5 ). In the ripening of the fruit, however, 
the ligneous matter and the starch seem to be again converted into 
sugar, under the influence of the vegetable acids which unripe fruits 
contain. 

Strictly speaking, the sugar contained in ripe fruits and in new honey 
is not grape-sugar (C 6 H 14 7 ), but a distinct variety of sugar known as 
fruit sugar or fructose, and having the composition (C 6 H ]2 6 ). This 
sugar has also been designated, in reference to 'its characteristic feature, 
uncrystallisable sugar, and its production seems to constitute an interme- 
diate stage in the transition of starch, cellulose, and cane-sugar into grape- 
sugar. Hence it is found that if the ebullition with diluted sulphuric 
acid be arrested as soon as the liquid becomes sweet, no crystals can be 
obtained, but on farther ebullition, the fructose is converted into crystal- 
lisable glucose. When honey is kept for some time, the fructose gra- 
dually becomes converted into a crystalline mass of glucose. The same 
change is seen to take place in raisins, which contain granules of glucose, 
though the fresh grapes contain only fructose. 

The uncrystallisable sugar forms the chief ingredient of molasses and 
treacle, for although the fresh juice of the sugar-cane contains no fructose, 
the treatment to which it is subjected in the extraction of the sugar occa- 
sions a copious formation of the uncrystallisable sugar at the expense of 
the cane-sugar. The simple ebullition of a solution of cane-sugar for a 
considerable period is said to convert a portion of it into fructose, and if 
a minute quantity of any uncombined acid be present, the change takes 
place very rapidly. Pure cane-sugar dissolved in water gradually changes 
into fructose when exposed to the light. 



492 MANUFACTURE OF SUGAR. 

354. Extraction of cane-sugar. — In the extraction of sugar from the 
sugar-cane, the latter is cut before the period of flowering, when, as might 
be expected, this soluble nutriment of the plant is most abundant. For 
a similar reason, the canes are cut off close to the ground, since in the 
higher joints of the cane much of the sugar has already been consumed 
for their development. 

A specimen of sugar-cane from Martinique was found to contain — 

Juice, . . . . 90*1 
Woody fibre, . . 9-9 



100-0 



So that, theoretically, 100 parts of cane should yield as much as 90 parts 
of juice. The canes are crushed between iron cylinders, which express, 
under the best arrangements, only 65 parts of juice from 100 of cane. It 
has been found possible to increase the yield by steaming the canes before 
submitting them to a final pressure. The juice thus expressed contains 
about 18 per cent, of sugar, together with the usual components of the 
sap of plants, such as vegetable acids, albumen, salts, &c. 

In the tropical climate in which the extraction is conducted, the albu- 
men of the juice speedily alters when exposed to the air, and excites 
fermentation in the sugar, by which a considerable quantity would be 
lost. If the fresh juice were heated to coagulate the albumen, the free 
acid contained in it would change a portion of the sugar into the uncrys- 
tallisable variety. To avoid this, the juice is mixed with g-^-g-th part of 
slaked lime, and is then heated to 140° F. in large flat copper pans. The 
coagulated albumen rises to the surface of the heavy syrup, and forms a 
thick scum, which is taken off, and the clear syrup is evaporated till it is 
strong enough to crystallise, when it is run off into shallow wooden vats, 
and allowed to cool for 24 hours. When briskly stirred, it congeals to a 
semi-solid mass of crystals, which are allowed to drain for three weeks in 
casks with perforated bottoms. The raw sugar thus obtained, after dry- 
ing in the sun, is sent into commerce, the drainings being styled molasses 
or treacle. The weight of raw sugar seldom exceeds xV^h of the juice, 
that is, about half the quantity which the juice is known to contain, the 
remainder having been converted into uncrystallisable sugar during the 
process of extraction. The loss is found to be materially diminished by 
jthe use of vacuum pans, in which the evaporation of the syrup is con- 
ducted under diminished pressure, and therefore at a lower temperature. 
Greater economy is also introduced into the manufacture by the use of 
the crushed canes as fuel for the evaporating fires, and by restoring their 
ashes to the land as food for ensuing crops. The skimmings of the clari- 
fied juice are also advantageously used as manure. 

The raw sugar obtained by the process just described contains about 
60 per cent, of pure cane-sugar, the remainder consisting of water, un- 
crystallisable sugar, colouring matter, and various salts and other foreign 
substances derived from the cane-juice. 

In the ordinary process of sugar-refining, two or three parts of raw 
sugar are dissolved in one part of water containing a little lime in solu- 
tion, and mixed with three or four parts of ground bone-black for every 
hundred of sugar ; a small quantity of serum of bullock's blood is also 
sometimes added. This mixture is heated by the passage of steam through 
it, when the albumen of the serum is coagulated, and rises to the surface 



SUGAE-KEFINING. 493 

in the form of a scum which entangles the floating impurities as well as 
the bone-black, and leaves the syrup much lighter in colour, a consider- 
able part of the colouring matter having been removed by the charcoal. 

The syrup is then filtered through a thick layer of coarsely powdered 
bone-black, and is thus rendered perfectly colourless and ready for evapora- 
tion, which is conducted in a boiler with double sides, so that it may be 
heated by steam admitted between the two, and furnished with a dome 
from which the air may be exhausted in order to allow the evaporation 
to be conducted at a lower temperature, as well as out of contact with 
the atmospheric oxygen, so as to diminish as far as possible the produc- 
tion of uncrystallisable sugar. The boiling down of the syrup, which 
would require a temperature of 230° F. at the ordinary pressure, may 
thus be conducted at 160° F. When sufficiently evaporated,* the syrup 
is transferred to a heated vat, where it is" stirred until a confused 
crystallisation commences, and is then drawn off into inverted sugar- 
loaf moulds of iron or earthenware, and allowed to crystallise during 
about 20 hours. The crystalline mass is then allowed to drain by the 
withdrawal of a plug at the apex of the inverted cone, and is washed 
with a little pure syrup to remove adhering colouring matter, after 
which the loaf is dried in an oven and finished by turning in a lathe. 

The operation of washing with syrup is often referred to as claying, 
being sometimes effected by placing some powdered sugar upon the base 
of each loaf, and over this a cream of pure pipe-clay, the water drain- 
ing from which dissolves the powdered sugar, and the syrup thus 
formed washes the loaf. The object of the clay appears to be simply 
to allow the water to flow gradually through the sugar. 

The process of refining is sometimes shortened by washing the raw 
sugar with strong syrup, so as to remove the bulk of the impurities at 
the commencement, and a very ingenious method, known as the centri- 
fugal process, has been devised for separating the syrup from the sugar 
thus washed. The pasty mixture of sugar and syrup is introduced into 
a cylinder of strong close metallic gauze, which is rapidly turned upon 
its axis, when the liquid syrup of course flies off through the apertures 
of the gauze, and is collected by a box surrounding the cylinder. A fresh 
quantity of syrup is then introduced, and separated in the same manner, 
so that the washing may be rapidly carried as far as may be deemed 
expedient. 

355. During the wars of Napoleon, when the importation of sugar into 
France was suspended, this substance was extracted from the beet-root, 
and this process still forms a very important branch of French industry. 

The white beet only is employed, on account of the difficulty of separat- 
ing the colouring matter existing in the juice of the red variety. The 
juice contains about ten per cent, of cane-sugar, half of which only is 
usually obtained in the crystallised state. The process adopted for extract- 
ing it does not differ in principle from that applied to the juice of the 
sugar-cane. 

Cane-sugar is also extracted in the United States from the sap of the 
sugar-maple, which is collected, usually in the spring, from deep incisions 
through the bark, into each of which a pipe of reed or elder is inserted 

* The state of concentration of the syrup is known by the degree of viscidity which it 
exhibits between the finger and thumb, by the length of the thread to which it may be 
drawn, and by the mode in which this curls after breaking. 



494 CHEMICAL PROPERTIES OE THE SUGARS. 

to conduct the juice into pans placed for its reception, whence it is re- 
moved before it has had time to become changed by fermentation. The 
juice is evaporated rapidly, and the raw crystalline mass sold without 
further refining. On an average, each tree furnishes about six pounds of 
sugar during the season. 

Sugar-candy consists simply of large rhomboidal prismatic crystals of 
sugar deposited upon strings stretched across crystallising troughs, in 
which a strong syrup is slowly evaporated at about 1 70° F. 

Barley-Sugar is prepared by evaporating the syrup beyond the crystal- 
lising point, till it solidifies, on cooling, to a vitreous mass, which is poured 
out on a cold surface and manipulated to the requisite forms. When 
kept for some time, the transparent barley-sugar becomes crystalline and 
opaque. 

Caramel (C 12 H 18 9 ) is a dark brown substance produced by the action 
of a temperature of about 400° F. upon melted sugar. It is very soluble 
in water, and gives an intensely brown liquid, for which reason it is 
employed for colouring sauces, gravies, brandy, wines, &c. 

356. Chemical properties of the sugars. — Although cane- and grape-sugar appear to 
be essentially indifferent substances, they are remarkably prone to form combina- 
tions with many basic metallic oxides. Thus a solution of cane-sugar is capable of 
dissolving a large quantity of lime, forming a compound (CaO.C l2 H 22 O n ) which is 
much more soluble in cold than in hot water, so that on boiling the transparent 
solution it becomes perfectly opaque, but resumes its transparency on cooling. This 
has been applied for separating the crystallisable sugar from molasses, the compound 
of sugar and lime precipitated by boiling being re-dissolved in cold water and treated 
with carbonic acid to separate the lime. 

On boiling the hydrated oxide of lead with a solution of sugar, it is dissolved, 
and as the solution cools, a white powder is deposited, which has the composition 
2PbO.C 12 H 18 9 .H 2 0, the water being expelled at a temperature of 212°. The com- 
position of this compound would lead to the belief that cane-sugar contains two mole- 
cules of constitutional water, and that its formula should be written C 12 H 18 9 .2H 2 0. 
By carefully heating cane-sugar, the compound, C 12 H 20 O 10 , saccharide, has been 
obtained, and if this be further heated it yields C 12 H 18 9 , caramel. When a solution 
containing 1 part of salt and 4 parts of sugar is allowed to evaporate sponta- 
neously, it deposits a deliquescent compound containing 2(NaCl.C 12 H 18 9 ) 3H 2 0. 

Many metallic oxides form compounds with sugar, which are readily soluble in 
alkaline liquids, so that the addition of sugar to solutions of the oxides of copper and 
iron, for example, prevents the precipitation of these oxides by the alkalies. 

Grape-sugar also combines with many bases. The compounds which it forms with 
the alkalies are very unstable, and their solutions, which are at first alkaline, soon 
become neutral in consequence of the conversion of the grape-sugar into glucic acid 
(H 3 C 12 H 15 9 ) by the loss of the elements of water. 

By saturating a solution of grape-sugar with common salt, a liquid is obtained which 
deposits well-defined crystals, having the composition 2(C 6 H 12 6 ).NaCl.H 2 0. When 
dried at 212° it becomes 2(C 6 H 12 6 ).NaCl. The true formula of grape-sugar is 
obviously C 6 H l2 6 .H 2 0, for if it be dissolved in hot strong alcohol (which dissolves 
far more grape-sugar than cane-sugar) it crystallises on cooling, in prisms, which 
have the formula C 6 H 12 6 . A molecule of water may also be expelled from ordinary 
grape-sugar at 212° F. 

The action of sulphuric acid upon cane- and grape-sugar is very different ; the 
former is carbonised and completely decomposed, whilst the latter combines with 
the sulphuric acid to form sulphosaccharic acid, which yields soluble salts with lime 
and baryta.* 

The optical properties of solutions of the sugars are now often turned to account 
for their identification, and even for the determination of their quantities. Grape- 
sugar and cane-sugar both rotate the plane of polarisation of a ray from left to right, 
cane-sugar having rather a more powerful action, but the un crystallisable fruit-sugar 

* Ethyle-glucose, a bitter, fragrant, oily substance, has been obtained by acting upon 
grape-sugar with bromide of ethyle and potash ; it may be represented by the formula 
C e H 8 (C 2 H s ) a O,. 



GUN-COTTON — PYROXYLINE. 495 

rotates the plane in the opposite direction, from right to left. If a solution of cane- 
sugar, possessing the rotatory power from left to right, be heated with hydrochloric 
acid, it acquires the power of rotating the plane of polarisation from right to left, in 
consequence of the conversion into uncrystallisable sugar. 

Starch-sugar exhibits three different modes of action upon polarised light, for a 
solution which has been kept some hours rotates the plane of polarisation only half 
as much as the freshly made solution ; and if the sugar prepared from malt be dis- 
solved in water, the solution has thrice the rotatory power which it possesses after 
being kept, and its rotatory power is one-third higher than that of the freshly 
dissolved starch-sugar. All these may be reduced at once to the lowest rotatory 
power by heatiug them nearly to ebullition and allowing them to cool. 

357. Mannite (C 6 H 14 6 ), the sweet principle of manna (the concrete juice of the 
Fraxinus ornus), has already been noticed as one of the products of that peculiar 
kind of fermentation known as the viscous, to which beet-root juice is especially 
liable. It is also found in certain mushrooms, in sea weeds, celery, asparagus, and 
onions. By treating manna with hot alcohol, and allowing the filtered solution to 
cool, the mannite may be obtained in beautiful prismatic crystals, which have a sweet 
taste, and dissolve readily in water. Mannite differs widely from cane- and grape- 
sugar in not fermenting when placed in contact with yeast ; and this circumstance, 
taken in conjunction with its composition, which differs so much from that of other 
members of the saccharine group, has always led to the belief that it was not pro- 
perly classed among these. 

Recent investigations have given it a place by the side of glycerine, the sweet 
principle of fats and oils,, as will be seen hereafter. 

GlycyrrMzine, the sweet principle of the liquorice root, somewhat resembles man- 
nite, but does not crystallise. 



GUN-COTTON AND SUBSTANCES ALLIED TO IT. 

358. Starch, the sugars, and cellulose, when acted on by the strongest 
nitric acid, furnish compounds which are remarkable for their explosive 
character, and are formed by the substitution of nitric peroxide (N0 2 ) for 
a portion of the hydrogen. By far the most important of these is 
pyroxyline (irvp, fire, £v\ov, wood), which is produced by the action of 
nitric acid upon the different forms of woody fibre, including wood, 
cotton, and paper. 

If a piece of white unsized paper (filter -paper) be soaked for a few 
minutes in the strongest nitric acid (sp. gr. 1*52),, then washed in a large 
volume of water and allowed to dry, it will be found to have suffered 
little alteration in appearance or texture, but to have acquired the pro- 
perty of burning with almost explosive violence on the application of a 
ilame or even of a moderately heated glass rod. This is due to the 
presence, in the altered paper, of a quantity of oxygen in the form of 
N0. 2 (nitric peroxide), which serves to burn up the paper very rapidly, 
rendering it in great measure independent of any extraneous supply of 
oxygen. The N0 2 has been introduced into the paper in the place of an 
equivalent quantity of hydrogen, which has been converted into water by 
the third atom of oxygen in the nitric acid (HN0 3 ). 

The pyroxyline so obtained, however, is always associated with a 
quantity of unaltered paper, for the water which is formed by the oxida- 
tion of the hydrogen, dilutes the remaining nitric acid, so that unless a 
very large proportion of nitric acid were employed, the acid would become 
so far weakened towards the close of the operation as to be incapable of 
converting the last portions of paper into pyroxyline. Moreover, since 
each fibre composing the paper is a very minute tube, often folded several 
times, it is not possible for the nitric acid to penetrate its entire substance 
unless the paper be soaked in it for a long time. 



496 



MANUFACTURE OF GUN-COTTON. 




Fig. 291. 



In order to effect a more complete conversion of the woody fibre into 
pyroxyline, the nitric acid must be mixed with strong sulphuric acid, 
which will combine with the water produced by the action of the nitric 
acid upon the hydrogen of the fibre, and will thus virtually maintain the 
nitric acid at its greatest strength throughout the operation. Cotton 
wool, from the looseness of its texture, is more easily converted into 
pyroxyline than paper. 

The following proportions may be recommended for the preparation of gun-cotton 
on a small scale : — Dry 1000 grains of pure nitre (p. 424) at a very moderate heat, 
place it in a dry retort (fig. 291), pour upon it 10 drms. (by measure) of strong sul- 
phuric acid, and distil until 6 drms. 
of nitric acid have passed over 
into the receiver. Dry some pure 
cotton wool, and weigh out 30 grains 
of it. Mix 2§ measured drachms of 
the nitric acid with an equal volume 
of strong sulphuric acid in a small 
beaker. Allow the mixture to cool, 
immerse the cotton wool, pressing 
it down with a glass rod, cover the 
beaker .with a glass plate, and set 
it aside for fifteen minutes. Lift 
the cotton out with a glass rod, 
throw it into at least a pint of water, 
and wash it thoroughly in a stream 
of water till it no longer tastes acid or reddens blue litmus paper. Dry the cotton by 
exposure to air or at a very moderate heat. 

Very great attention has been paid to the manufacture of gun-cotton 
during the last few years, with the object of producing a perfectly uniform 
product which might be employed as a substitute for gunpowder. 

The following is an outline of the process now generally adopted for 
the production of large quantities of gun-cotton by Abel's process : — 

359. Manufacture of gun-cotton. — The cotton is employed in the form of the waste 
cuttings from spinning machines (cotton waste). 

The proportions in which it is found most advantageous to mix the nitric and 
sulphuric acids are 1 part of nitric acid (sp. gr. 1'52) and 3 parts by weight (or 2 "45 
by volume), of sulphuric acid (sp. gr. 1'84). These proportions of the acids are 
placed in separate stoneware cisterns with taps, and allowed to run simultaneously, 
in slow streams, into another stoneware cistern furnished with a tap and an iron lid, 
through a second opening in which an iron stirrer is employed to mix the acids 
thoroughly. The mixture is set aside for several hours to become perfectly cool. 

A quantity of the mixed acids is drawn off into a deep stoneware pan standing in 
cold water, and provided with a perforated iron shelf, upon which the cotton may be 
drained. The well-dried cotton is immersed, a little at a time, in the acid, and 
stirred about in it for two or three minutes with an iron stirrer. It is then placed 
upon the perforated shelf, and the excess of acid squeezed out with the stirrer. 
Enough acid is drawn from the cistern to replace that which has been absorbed by 
the cotton, and more cotton is treated in the same way. Since a considerable rise of 
temperature is produced by the action of the nitric acid upon the cotton, it is neces- 
sary to keep the pan surrounded with cold water. A large proportion of the cotton 
is doubtless converted into gun-cotton in this preliminary immersion in the mixed 
acids ; but in order to convert the remainder, it is necessary to allow the cotton to 
remain in contact with the acid for a much longer period, so as to ensure its penetra- 
tion into every part of the minute twisted tubes of the fibre. The preliminary 
immersion of each skein has the advantage of wetting every part with the acid, which 
could not be so certainly effected if several skeins were thrown at once into a jar, 
and of preventing the great accumulation of heat which would ensue if the entire 
chemical action were allowed to take place upon a number of skeins at the same 
time. The amount of heat evolved during the subsequent soaking in acid is com- 
paratively small. 

The skeins are next transferred to a jar with a well-fitting cover, in which they 



COMPOSITION OF GUN-COTTON. . 497 

are pressed down and completely covered with, the mixed acids, of which from 10 to 
15 times the weight of the cotton will be required, according to the closeness with 
which the skeins are packed in the jar. The jar is placed in cold water, and the 
cotton allowed to remain in the acid for 24 hours. 

The skeins are then removed, with the aid of an iron hook, to a centrifugal 
extractor, which is a cylinder made of iron or copper gauze, through which the 
liquid is whirled out by the rapid rotation of the cylinder upon an axle. In this 
they are whirled, at first slowly, and afterwards at 800 revolutions per minute, 
during ten minutes, when the bulk of the acid is separated. In order to wash away 
the remainder of the acid, the cotton is plunged, suddenly, in very small portions, 
into a large volume of water ; for if the water were allowed to come slowly into con- 
tact with the mixed acids, so much heat would be evolved as to decompose a portion 
of the pyroxyline. The cotton is then drained in the centrifugal extractor, and 
again rinsed in much water. After two or three rinsings it is reduced to pulp in a 
rag-engine such as is employed in paper-mills. The pulp is thoroughly washed by 
being well stirred up by a poaching -engine for about 48 hours in a stream of warm 
water, so as to remove every trace of acid, which is assisted by rendering the water 
alkaline with a little lime or carbonate of soda. The pulp is then drained, moulded 
into discs or any other required form, condensed by hydraulic pressure until it has 
about the same specific gravity as water, and dried upon heated plates. As it leaves 
the hydraulic press, the cotton contains about one-fifth of its weight of water, so that 
it may, if required, be cut up or bored without danger of explosion. 

360. Chemical composition of gun-cotton. — Perfectly pure gun-cotton 
contains carbon, hydrogen, nitrogen, and oxygen, in proportions which 
correspond to the empirical formula C 6 H 7 N 3 O n . The determination of 
its rational formula is attended with difficulty, because, being an indiffe- 
rent substance, it does not form definite combinations with other bodies 
of known molecular weight, and it is, of course, impossible to arrive at its 
volume in the state of vapour, which so frequently affords valuable assist- 
ance in fixing a rational formula. Having regard to the mode of its for- 
mation from cellulose (cotton), C 6 H 10 O 5 , by the action of nitric acid, 
without evolution of gas, the most probable rational formula appears to 
be C 6 H 7 (N0 2 ) 3 5 , which represents it as tr (nitrocellulose, or cellulose in 
which three molecules of nitric peroxide have been substituted for three 
atoms of hydrogen. The action of nitric acid upon the cotton would then 
be represented by the equation — 

C 8 H„,0 5 + 3(HN0 3 ) = C 6 H 7 (N0 2 )A + 3H 2 . 

Cellulose. Trinitrocellulose. 

According to this equation, 100 lbs. of cotton 'should furnish 183 lbs. 
of gun-cotton ; but in practice only about 177 lbs. are obtained, a part of 
the deficiency being accounted for by unavoidable mechanical loss, and by 
small quantities of foreign matters dissolved out by the acids. 

That the nitrogen is really present in the gun-cotton in the form of 
nitric peroxide (N0 2 ), as implied in the above formula, is indicated by 
the action of potash, which dissolves the gun-cotton, and yields a solution 
containing nitrate and nitrite of potash, exactly the products which are 
formed by the action of potash upon nitric peroxide (p. 141). 

Another reaction of gun-cotton which supports the above view of its 
constitution, is that with hydrosulphate of potassium. If some hydrate of 
potash be dissolved in alcohol, and the solution saturated with gaseous 
hydrosulphuric acid, an alcoholic solution of hydrosulphate of potassium 
(KHS) is obtained ; and if the gun-cotton be immersed in this solution, 
and gently heated, it will be rapidly reconverted into ordinary cotton, and 
nitrite of potash will be found in the solution — 

C 6 H 7 (£T0 2 ) 3 5 + 3(KHS) = C 6 H 10 O 5 + 3(KN0 2 ) + S 3 , 

Trinitrocellulose. Cellulose. 

This is the so-called synthetical method of determining the composition 

2 i 



498 PRODUCTS OF EXPLOSION OF GUN-COTTON. 

of gun-cotton, for of course 183 parts of the latter should furnish 100 parts 
of cotton. 

361. Products of the exjilosion of gun-cotton. — From what has been 
stated with respect to the products of explosion of gunpowder (p. 423), it 
might be expected that those furnished bj gun-cotton would vary accord- 
ing to the conditions under which the explosion takes place. When a 
mass of the gun-cotton wool is exploded in an unconfined state, the 
explosion is comparatively slow (though appearing to the eye almost in- 
stantaneous), since each particle is fired by the flame of that immediately 
adjoining it, the heated gas (or flame), escaping outwards, so that some 
time elapses before the interior of the mass is ignited. But when the 
gun-cotton is enclosed in a strong case, so that the flame from the portion 
first ignited is unable to escape outwards, and must spread into the interior 
of the mass, this is ignited simultaneously at a great number of points, 
and the decomposition takes place far more rapidly ; a given weight of 
cotton being thus consumed in a much shorter time, a far higher tempera- 
ture is produced, and the ultimate results of the explosion are much less 
complex, as would be expected from the well-known simplifying effect of 
high temperatures upon chemical compounds. 

If a tuft of gun-cotton wool be placed at the bottom of a tall glass cylinder, and 
inflamed by a heated wire, it will be seen that, immediately after the explosion, 
the gas within the cylinder is colourless, but it soon becomes red, showing that nitric 
oxide was present among the products, and became converted into nitrous acid and 
nitric peroxide by the oxygen of the air. Of course these are strongly acid, and 
hence the acid character of the moisture deposited in the bairel of a fowling-piece in 
which gun-cotton cartridges are employed. In order to avoid corrosion of the barrel 
it is necessary that it should be cleaned at the end of the day's shooting. 

A little hydrocyanic acid can be detected among the products of combustion of 
loose gun-cotton. 

The determination of the products of explosion of confined gun-cotton 
has been effected by Karolyi in the same manner as in the case of gun- 
powder (see p. 418), by enclosing the cotton in a cast-iron cylinder, strong 
enough to resist bursting until the combustion of the last portion of 
the charge, which was suspended in an iron globe exhausted of air, 
and exploded by the galvanic battery ; the total volume of the gases 
collected in the globe was then determined and subjected to analysis. 
The amount of gun-cotton fired was about 150 grains. Unfortunately, 
the formula given for the sample of gun-cotton experimented on does not 
represent the trinitrocellulose which constitutes pure gun-cotton, being 
C, 2 H 17 N 5 19 , instead of C 12 H l4 N 6 22 (representing 2 molecules of trinitro- 
cellulose), but the difficulty attending the exact ultimate analysis of gun- 
cotton is so great, that there is greater probability of the analysis being 
incorrect than of the composition of the cotton having really differed mate- 
rially from that of trinitrocellulose. 100 grains of gun-cotton gave a quan- 
tity of aqueous vapour and gaseous products, calculated to occupy, at 
60 o, 8 F. and 29*06 in. Bar., 325*5 cubic inches, supposing the aqueous 
vapour to remain uncondensed at that temperature. The analysis of the • 
gas proved that 100 volumes of the products of explosion contain — 
Aqueous vapour, . . 25*34 vols. 
Carbonic oxide (CO), 



Carbonic acid (C0 2 ) 
Nitrogen, . 
Hydrogen, 

Marsh-gas (CH 4 ), 



28-95 

20*82 

12-67 

3*16 

7*24 

98*18 






EFFECTS OF GUN-COTTON AND GUNPOWDER COMPARED. 499 

If the marsh-gas and hydrogen be left out of consideration, the follow- 
ing equation will account for the other products of the explosion, sup- 
posing the gun-cotton to be pure trinitrocellulose — 

2C 6 H 7 (N0 2 ),0 5 = 9CO + 3C0 2 + 7H,0 + N e . 

According to this equation, 100 grains of gun-cotton should furnish 356 
cubic inches of gas and vapour, instead of 325 5 as determined by experi- 
ment, and the volumes of the products should be — 



Aqueous vapour, . 


28 vols 


Carbonic oxide, 


36 „ 


Carbonic acid, 


12 „ 


Nitrogen, 


12 „ 



which do not agree with the experimental results. It is not to be ex- 
pected, however, that one simple equation should correctly represent all 
the products of such a decomposition (see p. 420). 

A cubic inch of compressed gun-cotton, of the same density as water, 
weighs about 250 grains, and would evolve, according to the above 
equation, 865 cubic inches of gas and vapour at 60° F., supposing the 
steam to be capable of remaining uncondensed. 

A cubic inch of gunpowder, of density 1*75, weighs about 440 grs., 
and would evolve by calculation (p. 420) about 390 cub. in. of gas at 60° F. 
This would become 4156 cubic inches at the calculated temperature of 
the explosion, corresponding to a pressure of about 26 tons per square 
inch. The quantity of heat generated in the explosion of gun-cotton has 
not been determined, but if it be identical with that evolved by gun- 
powder, the temperature of the flame of gun-cotton would be 2166° C. 
(= 3930° F.), a temperature much lower than in the case of gunpowder, 
because the specific heats of the products from gun-cotton are higher. At 
that temperature, the 865 cubic inches of gas generated by a cubic inch 
of gun-cotton would become about 7720 cubic inches, and would exert 
a pressure of about 50 tons upon the square inch, or nearly twice that 
calculated for gunpowder. 

The experiments hitherto made have been unfavourable to the employ- 
ment of gun-cotton as a substitute for gunpowder^in artillery, on account 
of the injury which its violent explosion occasionally inflicts upon the 
gun. For use in fowling-pieces, the gun-cotton pulp is diluted with a 
proportion of ordinary cotton pulp, and made into a kind of paper which 
is rolled up to form the cartridges. Although such cartridges leave a con- 
siderable carbonaceous residue when fired on a plate, they leave little or 
no residue when fired under pressure. 

If a piece of compressed gun-cotton be kindled with a hot wire it 
burns rapidly away, producing a large volume of flame, but without 
any explosive effect.* In order that gun-cotton fired in this manner 
might be used for destructive purposes, it was found necessary to confine 
it in strong cases, so that the flame of the portion first ignited should be 
employed in raising the temperature of the rest to the exploding point. 

The discovery, made by E. O. Brown, of a method by which the uncon- 
Uned gun-cotton could be made to explode with most destructive violence, 

* Too much stress, however, should not be laid upon this as rendering gun-cotton maga- 
zines safer in case of fire than gunpowder magazines. The experiment with gunpowder 
mentioned at page 423, shows that if all the particles of an explosive be raised at once to 
nearly the inflaming point, the first particle which inflames will cause the detonation of 
the remainder. Since the inflaming point of gun-cotton is low, the above condition would 
be easily fulfilled in a conflagration. 



500 PROPERTIES OF GUN-COTTON. 

has opened a new career to this material, rendering it far superior to 
gunpowder for all blasting operations, torpedoes, &c. It is only neces- 
sary to explode in contact with the compressed cotton a detonating fuze, 
consisting of a little tube of quill or thin metal charged with a few grains 
of fulminate of mercury, to cause the cotton to detonate with extreme 
violence ; and such detonation can be communicated along a row of 
pieces of compressed cotton placed at short distances from each other. 

This capability of undergoing what may be termed sympathetic explo- 
sion is by no means confined to gun-cotton. Previously to Brown's dis- 
covery, ISTobel had shown it to exist in the case of nitroglycerine, and 
Abel afterwards proved that most explosives, including even gunpowder, 
can be made to detonate in a similar manner. The modus operandi of 
the detonating fuze has not, however, been satisfactorily explained. It 
would at first appear to act merely by mechanical concussion, but the 
results obtained by Abel throw some doubt upon this. 

The very destructive effect of the gun-cotton exploded in this way 
is, of course, due to the sudden manner in which the whole mass is 
resolved into gaseous products. 

362. Properties of gun-cotton compared with those of gunpowder. — 
Gun-cotton is more easily exploded than gunpowder ; the latter requires 
a temperature of at least 600° F., whilst gun-cotton may explode at 277° F., 
and must explode at 400° F. It is very difficult to explode gunpowder 
by percussion, even between a steel hammer and anvil ; but gun-cotton 
invariably detonates in this way, though the explosion is confined to the 
part under the hammer. The explosion of gun-cotton is, of course, unat- 
tended by any smoke, a most important advantage in mines, the atmo- 
sphere of which is sometimes rendered almost intolerable by the smoke of 
gunpowder used in blasting. The absence of residue from the gun-cotton 
prevents the fouling of guns, and renders it unnecessary to sponge them 
after each discharge, for the amount of incombustible mineral matter pre- 
sent in the cotton is very small (from 1 to 2 per cent.), and is entirely 
scattered by the explosion. 

It has already been mentioned that the explosion of gun-cotton does 
not impart so much heat- to the metal of the gun as that of powder, the 
difference being so great that, after firing 100 rounds with gun-cotton, the 
gun was not so much heated as after 30 rounds with gunpowder. This 
important advantage of gun-cotton may be due either to the lower tem- 
perature of its flame, or to the circumstance that the charge of gun-cotton 
is only one-third of the charge of powder, that the explosion of the former 
is so much more rapid, leaving less time for the communication of heat 
to the metal, and that there are no highly -heated solid products left in 
contact with the gun. Gun-cotton wool may be fired upon the palm of 
the hand with impunity, or upon a heap of gunpowder without kindling 
it ; although it cannot be doubted that the temperature of the flame is 
really much higher than the inflaming point of powder. That the recoil 
of a gun charged with gun-cotton is only two-thirds of that experienced 
with gunpowder, is probably due to the rapidity of the explosion, which 
allows less time for overcoming the inertia of the gun ; the difference in 
recoil taking the form of strain upon the metal composing the gun. 

It is evident, from the consideration of its manufacture, that gun-cotton 
is entirely uninjured by water, so that a store of this explosive might be 
immersed in water in case of need, and would be still serviceable after 



PREPARATION OF COLLODION. 501 

drying, whereas gunpowder is, of course, rendered useless by contact with 
water, which dissolves out the nitre. Even when exposed to very damp 
air, gunpowder is liable to injury from the effect of moisture in partially 
separating the nitre from the other ingredients, whilst gun-cotton only 
requires exposure to a dry atmosphere for a short time to render it fit 
for use. The proportion of moisture retained by gun-cotton, in the ordi- 
nary state of the atmosphere, is 2 per cent. 

As an objection to the employment of gun-cotton as a substitute for gun- 
powder, it has been asserted that the trinitrocellulose is liable to undergo 
spontaneous decomposition, which might at any time render the contents 
of a magazine unserviceable, or might even give rise to the evolution of a 
sufficient amount of heat to cause an explosion. The origin of this objec- 
tion is to be traced to the old process for preparing gun-cotton, in which 
the acids were not allowed to act upon the cotton for a sufficient length of 
time, so that the whole of the cotton was not converted into true gun- 
cotton, but some less stable substitution products were formed at the 
same time. Another cause of spontaneous alteration is the imperfect 
washing of the gun-cotton, whereby minute traces of acid are left in the 
fibre. All recent experiments, by Abel and others, appear to have proved 
that, considering its highly complex character, 2 mre gun-cotton is a very 
stable compound under ordinary conditions; although, when kept in a 
moist state, it developes traces of acid products, the temperature does not 
rise to any important extent, nor is the explosive quality of the material 
at all injured. 

363. Gun-cotton is somewhat harsher to the touch than ordinary cotton, 
and becomes remarkably electrical when rubbed between the dry fingers. 
It is insoluble in alcohol and ether, as well as in a mixture of these sol- 
vents, though ordinary specimens generally yield a small percentage of 
soluble matter when treated with a mixture of alcohol and ether, because 
they contain extraneous matters, such as the other substitution products 
to be mentioned presently. Acetic ether dissolves it, and so does a mix- 
ture of ordinary ether with ammonia. Strong sulphuric acid dissolves it 
without carbonisation, unless any unconverted cotton should happen to 
be present. 

364. Collodion cotton. — When cotton or paper is acted upon by a mix- 
ture of nitric and sulphuric acids containing more water than is present 
in that employed for the preparation of gun-cotton (p. 496), compounds 
are formed which contain less nitric peroxide, and are much less com- 
bustible than the trinitrocellulose, from which they are also distinguished 
by their solubility in mixtures of alcohol and ether. 

In order to render evident the relations between these compounds and 
gun-cotton, the formula of the latter must be trebled, when we have the 
following series of nitro-compounds produced by the mixtures of nitric 
acid, sulphuric acid, and water, to which they stand opposite- 



composition of the mixed acids. 



Products of their action on cellulose. 



C 18 H 23 (N0 2 ) 7 15 ' 
C 18 H 24 (N0 2 ) 6 15 



As might be expected, these compounds diminish in combustibility in 
proportion as the ls r 2 contained in them diminishes. The second is that 



502 XYLOIDINE — NITROMANNITE. 

employed for the preparation of photographic collodion, being dissolved 
for that purpose in a mixture of ether and alcohol. 

In order to prepare the soluble cotton for collodion, three measured ounces of ordi- 
nary nitric acid (sp. gr. 1 '429) are mixed with two ounces of water in a pint beaker. 
Nine measured ounces of strong sulphuric acid (sp. gr. T839) are added to this mix- 
ture, which is continually stirred whilst the acid is being added. A thermometer is 
placed in the mixture, which is allowed to cool to 140° F. ; 100 grains of dry cotton 
wool, in ten separate tufts, are immersed in the mixture for five minutes, the beaker 
being covered with a glass plate. The acid is then poured into another beaker, the 
cotton squeezed with a glass rod, and thrown into a large volume of water ; it is 
finally washed in a stream of water till it is no longer acid, and dried by exposure to 
air. (By adding to the acid which was drained out of the cotton, three drachms 
more sulphuric acid, and immersing another 100 grains of cotton for ten minutes, a 
second portion of soluble cotton may be obtained.) 

Collodion balloons. — These balloons may be made in the following manner : — 6 
grains of the collodion cotton, prepared according to the above directions, are dissolved 
in a mixture of 1 drachm of alcohol (sp. gr. "835) and 2 drachms of ether (sp. gr. *725), 
in a corked test-tube. The solution is poured into a dry Florence flask, which is 
then turned about slowly, so that every part of its surface may be covered with the 
collodion, the excess of which is then allowed to drain back into the tube. Air is 
then blown into- the flask through a long glass tube attached to the bellows (or to the 
blowpipe-table (fig. 131), as long as any smell of ether is perceptible. A pen-knife 
blade is carefully inserted between the flask and the neck of the balloon, which is 
thus detached from the glass all round ; a small piece of glass tubing is introduced 
for an inch or two into the neck of the balloon, so that the latter may cling round 
it. Through this tube air is drawn out by the mouth until one-half of the balloon 
has left the side of the flask and collapsed upon the other half ; by carefully twisting 
the tube, the whole of the balloon may be detached and drawn out through the neck 
of the flask, when it must be quickly untwisted, distended by blowing through the 
tube, tied with a piece of silk, and suspended in the air to dry. The average weight 
of such balloons is two grains. 

When collodion-cotton is kept for some time, especially if at all damp, 
it undergoes decomposition, filling the bottle with red fumes, and becoming 
converted into a gummy mass, which contains oxalic acid. 

365. Xyloidine is the name given to a highly combustible substance 
analogous to pyroxyline, which is obtained by dissolving starch in the 
strongest nitric acid, and diluting the solution with water, when the 
xyloidine falls as a white precipitate, which may be collected upon a 
filter, and washed till free from acid. The composition of xyloidine is 
C ? Hg(N0 2 ). 2 O g , representing starch (C 6 H 10 O 5 ), in which 2 molecules of 
nitric peroxide have been substituted for 2 atoms of hydrogen. 

Nitroma unite (C 6 H 8 (]Sr0 2 ) 6 6 ) is another explosive body of the same 
order, obtained by adding powdered mannite (C 6 H 14 6 ), in small portions, 
to a mixture of equal measures of the strongest nitric and sulphuric acids, 
which immediately dissolve it, and presently solidify to a mass of minute 
needles of nitromannite, which may be washed with a large volume of 
water, and crystallised from boiling alcohol. Under the hammer, nitro- 
mannite explodes with a very loud report. When heated, it fuses before 
exploding, 



PREPARATION OF WINE. 503 



WINE AND SPIRITS. 

366. Wine is essentially composed of 8 or 10 parts of alcohol, with 
85 or 90 of water, together with minute quantities of certain fragrant 
ethers, of colouring matter, of bitartrate of potash, and of the mineral 
substances derived from the grape-juice. Glycerine and succinic acid 
have also been found in wines, and appear to be constant secondary pro- 
ducts of the alcoholic fermentation (p. 485). 

Those wines in which the whole of the sugar has been fermented are 
known as dry wines ; whilst fruity wines still retain a considerable 
quantity of sugar. 

The preparation of wine differs from that of beer in the circumstance 
that no addition of ferment is necessary, the fermentation being excited 
by a substance present in the grape-juice. This juice contains, in addition 
to grape-sugar, vegetable albumen, tartrate" of potash, and the usual 
mineral salts found in vegetable juices. The husks, seeds, and stalks of 
the grape contain a considerable quantity of tannin, together with certain 
blue, red, and yellow colouring matters. 

When the expressed juice remains for a short time in contact with the 
air, the albuminous substances contained in it enter upon a state of change, 
exciting the vinous fermentation in the sugar, and a scum of yeast is 
formed upon the surface. If this fermentation takes place in contact with 
the husks of the dark grapes, the alcohol dissolves the colouring matter, 
and a red wine results ; whilst for the production of white wines, the 
husks, &c, are separated previously to the fermentation, and the juice is 
exposed as little as possible to the air. 

White wines are rather liable to become ropy from viscous fermenta- 
tion, but this is prevented by the addition of a small quantity of tannin, 
which precipitates the peculiar ferment. The tannin for this purpose is 
extracted from the husks and stalks of the grapes themselves. 

Red wines, such as port and claret, are often very astringent from the 
tannin dissolved out of the husks, &c, during the fermentation. Port 
wine, when freshly bottled, still retains in solution a considerable quantity 
of bitartrate of potash (KHC 4 H 4 O g ), but after it has been kept some time, 
and become more strongly alcoholic, this salt is deposited, together with 
a quantity of the colouring matter, in the form of a crust upon the side of 
the bottle. Thus a dark fruity port becomes tawny and dry when kept 
for a sufficient length of time, the sugar having been converted into alcohol. 

When the wine contains an excess of tartaric acid, it is customary to 
add to it some neutral tartrate of potash (K a C 4 H 4 6 ), which precipitates 
the acid in the form of bitartrate. 

The preparation of champagne is conducted with the greatest care. 
The juice or must is carefully separated from the marc or husk, and is 
often mixed with one per cent, of brandy before fermentation. After 
about two months the wine is drawn off into another cask, and clarified 
with isinglass dissolved in white wine, and added in the proportion of 
about half-an-ounce to 40 gallons. This combines with the tannin to 
form an insoluble precipitate, which carries with it any impurities floating 
in the wine. After another interval of two months, the wine is again 
drawn off, and a second clarification takes place; and in two months more 
the wine is drawn off into bottles containing a small quantity of pure 
sugar-candy dissolved in white wine. The bottles, having been securely 
corked and wired, are laid down upon their sides for eight or ten months, 



504 DISTILLED SPIRITS. 

during which time the fermentation of the newly added sugar takes 
place, and the carbonic acid produced dissolves in the wine, whilst a 
quantity of yeast is separated. In order to render the wine perfectly 
clear, the bottle is left for about three weeks in such a position that the 
deposit may subside into the neck, against the cork, which is then un- 
wired so that the pressure of the accumulated carbonic acid may force it 
out together with the deposit ; the bottle having been rapidly filled up 
with white wine, is again corked, wired, covered with tin foil, and sent 
into the market. Pink champagne is prepared from the must which is 
squeezed out of the marc after it has ceased to run freely, and contains a 
little of the colouring matter of the husk. The colour is also sometimes 
imparted by adding a little tincture of litmus. 

The proportion of alcohol in wines varies greatly, as will be seen from 
the following statement of the weight of alcohol in 100 parts of the wine : — 

from 15 to 17. 



J. Ul v } 

Sherry, 


„ 14 to 16. 


Champagne, . 


11-5. 


Claret," . . 


„ 8 to 9. 


Eudesheimer, 


„ 7 to 8-5 



Sherry contains from 1 to 5 per cent, of sugar, port from 3 to 7 per 
cent., and Tokay 17 per cent. ; in the last case, the sugar is increased 
by adding some of the must concentrated by evaporation to the wine 
previously to bottling. 

The bouquet or fragrance of wine is due to the presence of certain 
fragrant ethers, especially of oenanthic, pelargonic, and acetic ether, 
formed during the fermentation or during the subsequent storing of the 
wine. It is to the increased quantity of such fragrant ether that the 
superior bouquet of many old wines is due. 

367. Distilled spirits. — The varieties of ardent spirits are obtained 
from fermented liquids by distillation, so that they consist essentially of 
alcohol more or less diluted with water, and flavoured either with some 
of the volatile products of the fermentation, or with some essential oil 
added for the purpose. 

Brandy is distilled from wine, and coloured to the required extent 
with burnt sugar (caramel). Its flavour is due chiefly to the presence 
of oenanthic ether derived from the wine. The colour of genuine pale 
brandy is due to its having remained so long in the cask as to have dis- 
solved a portion of brown colouring matter from the wood, and is there- 
fore an indication of its age. TIence arose the custom of adding caramel, 
and sometimes infusion of tea, to impart the astringency due to the 
tannin dissolved from the wood by old brandy. 

Whisky is distilled from fermented malt, which has been dried over a 
peat fire, to which the characteristic smoky flavour is due. 

Gin is also prepared from fermented malt or other grain, and is flavoured 
with the essential oil of juniper, derived from juniper berries, added 
during the distillation. 

Rum is distilled from fermented molasses, and appears to owe its 
flavour to the presence of butyric ether, or of some similar compound. 

Arrack is the spirit obtained from fermented rice. 

Kirschwasser and maraschino are distilled from cherries and their 
stones, which have been crushed and fermented. 

Some varieties of British brandy and whisky are distilled from fer- 



V1NIC OR ET HYLIC CLASS OF ALCOHOLS. 



505 



mented potatoes, or from a mixture of potatoes and grain, when there 
distils over, together with ordinary alcohol, another spirit belonging to 
the same class, but distinguished from alcohol by its nauseous and irritat- 
ing odour. This substance, which is known as loolato-spirit, amylic 
alcohol, or f ousel oil (C 5 H 12 0) also occurs, though in very minute quantity, 
in genuine wine-brandy. The manufacturers of spirit from grain and 
potatoes remove a considerable part of this disagreeable and unwholesome 
substance by leaving the spirit for some time in contact with wood- 
charcoal. 



THE ALCOHOLS AKD THEIE DERIVATIVES. 

368. It has already been stated that alcohol is the type of a very im- 
portant class of compounds closely related to each other in composition 
and properties. 

The alcohols are all composed of carbon, hydrogen, and oxygen \ the 
members of the series represented by common alcohol always contain one 
atom of oxygen. The number of atoms of hydrogen is always an even 
number, exceeding by two the doubled number of atoms of carbon, so 
that the general formula of an alcohol of this series may be written 
thus, C }l H 2)l + 2 0. Thus, in ordinary or vinic alcohol, C 2 H 6 0, n = 2, in 
wood-spirit or methylic alcohol, CH 4 0, n = 1, in potato-spirit or amylic 
alcohol, C 5 H 12 0, n = 5. 

These alcohols constitute, therefore, a truly homologous series (p. 454) 
of which many members, however, remain to be discovered. 

The following table includes the alcohols of this series which are at 
present known : — 



Chemical Name. 


Source. 


Formula, 


Common Name. 


1. Methylic alcohol 


Destructive distillation of wood 


C H 4 


"Wood naphtha 


2. Ethylic 


>> 


Vinous fermentation of sugar 


C 2 H 6 


Spirit of wine 


3. Propylic 


> j 


Fermentation of grape-husks 


C 3 H 8 




4. Butylic 


>> 


Fermentation of beet-root . 


C 4 H 10 O 




5. Amylic 


j» 


Fermentation of potatoes 


C 5 H 12 


Fousel oil 


6. Caproic 


)5 


Fermentation of grape-husks 


C 6 H 14 




7. (Enanthic 


» i 


Distillation of castor-oil with ) 
potash ) 


C 7 H 16 




8. Caprylic 


J5 


Fermentation of grape-husks 


C 8 H 18 




10. Kutic 


>» 


Oil of rue 


^10^22^ 




12. Laurie 


>5 


Whale oil ...... 


C 12 H 26° 




16. Cetylic 


J ) 


Spermaceti 


C 16 H 34 


Ethal 


27. Cerylic 


>) 


Chinese wax 


C 27 H 56° 


Cerotene 


30. Melissic 


" 


Bees' wax 


C 30 H 62 O 


Melissine 



The usual gradation in properties attending the gradation in composi- 
tion among the members of a homologous series, is strikingly exemplified 
in the class of alcohols. The first eight members of the group, linked 
together as they are by an almost common origin (being derived, with 
one exception, from the fermentation of substances nearly allied, and that 
exception being a product of destructive distillation which may be re- 
garded as an accelerated fermentation), and by a regularly ascending com- 



506 



ALCOHOLS — ALDEHYDES. 



position, would "be expected to resemble each other in their properties 
far more closely than the other members of the class. Accordingly, we 
find that methylic, ethylic, propylic, butylic, amylic, caproic, oenanthic,* 
and caprylic alcohols, are all liquid at the ordinary temperature, that they 
all possess peculiar and powerful odours, and may be readily distilled 
unchanged. Among these, however, the gradation is not to be overlooked. 
The two' first, methylic and ethylic alcohols, may be mixed with water in 
all proportions, but the third, propylic alcohol, though freely soluble in 
water, is not so to an unlimited extent ; whilst butylic alcohol is less 
soluble, and amylic alcohol may be said to be sparingly soluble in water. 
Caproic alcohol, the next member, is insoluble in water ; whilst caprylic 
is not only insoluble, but possesses an oily character, leaving a greasy 
stain upon paper. 

In their boiling points, and the specific gravities of their vapours, a 
similar gradation is observed. 



Alcohol* 


Boiling Point. 


Vapour Density. 


Methylic, ....... 


149°- 9 F. 


1-12 


Ethylic, . . . 






173° 


1-61 


Propylic, . . 






205° 


2-02 


Butylic, . . . 






233° 


2-59 


Amylic, . . . 






269°-8 


3-15 


Caproic, . . . 






299°-309° 


3-53 


(Enanthic, .. . 






327°-343° 


— 


Caprylic, . .. 






356° 


4-50 



One molecule of each of these alcohols yields two volumes of vapour ; 
or, in other words; if a given weight of the alcohol corresponding to its 
molecular weight be converted into vapour, that vapour will occupy twice 
a& much space as would be occupied by one part of hydrogen at the same 
temperature and pressure. 

The higher members of the group of alcohols are solid fusible bodies 
more nearly approaching to waxy or fatty matters in their nature, and 
not susceptible of distillation without decomposition. Far less is known 
of these than of the alcohols containing less carbon. 

The true chemical definition of an alcohol of this series rests upon the 
circumstance, that under the influence of oxidising agents, it first parts 
with two atoms of hydrogen, and is converted into an aldehyde (alcohol 
dehydrogenated), and afterwards absorbs an atom of oxygen, yielding an 
acid. Thus, it has been already shown (p. 487), that vinic alcohol 
(C 2 H 6 0), when exposed to air under favourable conditions, yields alde- 
hyde, C 2 H 4 0, which, by absorbing oxygen, is converted into acetic 
acid, C 2 H 4 2 . 

The formation of an aldehyde would, therefore, be represented by the 



general formula- 



C n H 2n + 2 + = 



+ 2 

Alcohol 



and that of the corresponding acid by 
CXx-0 + 0. 



L 2* + : 

Alcohol. 



Aldehyde. 



CJT,, t O. 

Acid. 



+ H.,0 



H o 



This alcohol is of recent discovery, and has been little examined. 



ACETIC SERIES OF ACIDS. 



507 



In addition to this, a double molecule of each of these alcohols, by 
the loss of the elements of a molecule of water, yields an ether, corres- 
ponding to ordinary ether (C 2 H 5 ) 2 0, which differs from the double mole- 
cule of vinic alcohol, C 2 H 6 0, by the elements of a molecule of water. 

The general formula representing the derivation of an ether from an 
alcohol of the above series is — 



2C tt H 2n+2 

Alcohol. 



H 2 



(C n H 2n+1 ) 2 . 

Ether. 



Hence every alcohol has its corresponding aldehyde, acid, and ether, so 
that there are homologous series of aldehydes, acids and ethers, just as 
of the alcohols from which they are derived. 

The only members of the aldehyde and ether series which have received 
a large share of attention on account of their practical importance, are 
those derived from ordinary alcohol ; but theseries of acids contains many 
members of importance, to some of which no corresponding alcohols 
are yet known. 

The very important homologous series of acids'" composed after the 
general formula C„H 2 „0 2 , includes — 



Acid. 


Source. 


Formula. 


1. Formic acid, 


Red ants, nettles 


CH 2 2 


2. Acetic ,, 


Vinegar 






C 2 H 4 2 


3. Propylic „ 


Oxidation of oils 






G 3 H 6 2 


4. Butyric ,, 


Rancid "butter . 






C 4 H 8 2 


5. Valerianic acid 


Valerian root . 






C5H 10 O 2 


6. Caproic ,, 


Rancid butter . 






C 6 H 12°2 


7. CEnanthic ,, 


Oxidation of castor oi 


1 




C 7 H 14 2 


8. Caprylic ,, 


Rancid butter . 






C 8 H 16°2 


9. Pelargonic acid 


Geranium leaves 






^9^18^2 


10. Rutic or capric acid 


Rancid butter . 






^10-^20^'2 


11. Euodict ,, 


Oil of rue . 






CnH 22 2 


12. Laurie ,, 


Bay berries 






C 12 H 240 2 


13. Cocinic ,, 


Cocoa nut oil 






Ci 3 H 26 2 


14. Myristic ,, 


Nutmeg butter . 






C 14 H 28 2 


15. Benic ,, 


Oil of ben 






Ci5H 30 O 2 


16. Palmitic ,, 


Palm oil . 






^16^32 ^2 


17. Margaric ,, 


Olive oil ? 






^17^3402 


18. Stearic ,, 


Tallow . • . 






Cl8H360 2 


19. Balenie ,, 




Ci 9 H 38 2 


20. Butic 


Butter .... 


C 2 o-f-40^-'2 


21. Nardic ,, 




^2l-"42^2 


27. Cerotie „ 


Bees' wax 


C27H54O2 


30. Melissic ,, 


Bees' wax 


^30-"60^2 



A very gradual transition of properties is observable in the members of 

this extended series of acids. 

* Often spoken of as the acetic series of acids, or the fatty acid series. 
f Euw <$)}?, fragrant. 



508 



OLEF1NES OK OLEFIANT GAS HYDROCARBONS. 



The first nine members of the series are liquid, the remainder solid at 
common temperatures. Of the liquids, formic acid boils at 221° F., and 
the boiling points of the other members exhibit a gradual rise up to pelar- 
gonic acid, which boils at 500° F. The melting-points of the solid acids 
also ascend from 86° F. for rutic acid (C 10 H 20 O 2 ) to 192° F. for melissic 

( C 30 H 6<A)- 

Formic and acetic acids may be mixed with water in all proportions, 
like their corresponding alcohols, the niethylic and ethylic; propylic 
acid, though soluble to a great extent in water, resembles the correspond- 
ing alcohol in not mixing indefinitely with water. Butyric acid behaves 
in a similar manner. Valerianic, caproic, oenanthic, and caprylic acids are 
sparingly soluble in water. Pelargonic and capric acids are very sparingly 
soluble, and the remaining members of the series are very decidedly fatty 
acids, insoluble in water, and forming soaps with the alkalies. 

The members of the series of alcohols, under the action of powerful 
dehydrating agents, are capable of parting with the elements of a mole- 
cule of water, furnishing the members of a homologous series of Irydrocar- 
bons related to their corresponding alcohols, as olefiant gas or ethylene 
(C 2 H 4 ) is related to ethylic alcohol. 

The general formula for the production of the homologues of ethylene 
(or olefines) from the alcohols may be thus expressed — 

C n H 2n + 2 - H 2 = C„H 2n . 

The known members of this series of hydrocarbons are 



Name. 


Formula. 


Corresponding 
Acid. 


Corresponding 
Alcohol. 


1. Methylene . 


CH 2 


Formic 


Wood-naphtha 


2. Ethylene 


C 2 H 4 


Acetic 


Alcohol 


3. Propylene 


C 3 H 6 


Propylic 


Propylic 


4. Butylene . . 


C 4 H 8 


Butyric 


Butylic 


5. Amylene 


C 5 H 10 


Valerianic 


Fousel oil 


6. Caproylene . 


CeH 12 


Caproic 


Caproic 


7. (Enanthene . 


C 7 H 14 


(Enanthic 


(Enanthic 


8. Caprylene 


^8^16 


Caprylic 


Caprylic 


9. Elaene . . 


CgH-ig 


Pelargonic 




10. Paramylene . 


^10"20 


Rutic 


Rutic 


16. Cetylene 


C16H32 


Palmitic 


Ethal 


2 7. Cerotene 


C 27 H 54 


Cerotic 


Cerotene 


30. Melissene 


C30H6O 


Melissic 


Melissine 



Of these hydrocarbons, methylene, ethylene, and propylene are gaseous ; 
butylene is also a gas, but easily condensed to a liquid state; the re- 
mainder are liquid at the ordinary temperature, except cerotene and me- 
lissene which are solid. 

This series exhibits one of the best examples of polymerism or multiple 
relation of composition, each member of the series being represented by a 
formula which is a multiple by some whole number of that of the first 
member of the series. 



PREPARATION OF ABSOLUTE ALCOHOL. 509 

Since one molecule of each, of these hydrocarbons in the state of vapour 
occupies two volumes, it must follow, if their composition be correctly 
stated, that their vapour densities exhibit a multiple relation similar to 
that which exists between their formulae. 

That this is the case will be seen by the subjoined table, which illus- 
trates very clearly the importance of determining the specific gravity of 
the vapour of a volatile substance as a confirmation of the results of 
analysis : — 



Hydrocarbon. 


Specific gravity of vapour. 


Methylene, 


CH 2 


0-490 


Ethylene, 


C 2 H 4 . 


0-978 


Propylene,* 


C 3 H 6 


1-498 


Butylene, 


C 4 H 8 . 


1-852 


Amylene, 


C 5 Hi 


2-386 


Caproylene, 


C 6 H 12 


. - . 2-875 


Caprylene, 


C 8 H 16 


3-90 


Elaene, 


C 9 H 18 


4-48 


Paramylene 


^10"-20 


5-061 


Cetylene, 


^16^32 • 


8-007 



It will be observed that just as the formula of cetylene (C 16 H 3 . 2 ) is a 
multiple of that of methylene (CH 2 ) by 16, so, allowing for errors of 
experiment, the vapour density of cetylene (8 - 007) is 16 times that of 
methylene (0-490). 

369. Alcohol may be studied as the type of the class to which it gives 
a name. 

When any of the fermented or distilled liquors of commerce are sub- 
jected to distillation, the alcohol passes over during the first part of the 
process, mixed with a considerable quantity of water ; and if the distilla- 
tion be continued as long as any alcohol passes over, and the whole of the 
distilled liquid be measured or weighed, the quantity of alcohol present 
in the original liquid subjected to distillation, may be inferred (by refer- 
ence to a table) from the specific gravity of the aqueous spirit distilled 
from it, since the lighter it is the more alcohol it contains, the specific 
gravity of pure alcohol being 0-794. 

The strength of the spirit of wine of commerce is ascertained by deter- 
mining its specific gravity. That known as proof spirit has the specific 
gravity 0*920, and is so called because it is the weakest spirit which will 
answer to the rough proof of firing gunpowder which has been moistened 
with it and kindled. Any spirit weaker than this leaves the powder 
moist, and does not explode it. It is then said to be under proof, whilst 
a stronger spirit is spoken of as over proof 

Proof spirit contains by weight, in 100 parts — 

Water, . . 50-76 

Alcohol, . . 49-24 

A spirit would be spoken of as 30 per cent., for example, over proof , 
if 100 measures of it, when diluted with water, would yield 130 measures 
of proof spirit. A spirit 30 per cent, below proof contains, in every 1 00 
measures, 70 measures of proof spirit. By repeatedly rectifying or re- 

* These hydrocarbons are sometimes designated by names which refer to the multiple of 
CH 2 which they contain. Thus propylene, 3(CH 2 ), is sometimes called tritylene ; buty- 
lene, tetrylene ; caproylene, hexylene, &c. 



510 



PREPARATION OF ETHER. 



distilling the weak spirit obtained from a fermented liquid, collecting the 
first portions separately, a strong spirit may be obtained, containing 90 
per cent, of alcohol, but mere distillation will not effect a further separa- 
tion of the water. Weak spirit may be concentrated to a greater extent 
than this, by leaving it enclosed in a bladder for a considerable period, 
when the water exudes through the bladder more readily than the alcohol, 
so that the latter accumulates in the mixture to the amount of 95 per 
cent. 

Another method of separating a great part of the water consists in add- 
ing dry carbonate of potash to the weak spirit as long as it is dissolved, 
when the mixture separates into two layers, the lower consisting of solu- 
tion of carbonate of potash in water, and the upper one of spirit, contain- 
ing 89 per cent, of alcohol. By effecting the separation by means of car- 
bonate of potash in a graduated tube, this method is sometimes employed 
for roughly ascertaining the proportion of alcohol in a fermented or 
distilled liquid, the foreign matters in which prevent any safe inference 
from the specific gravity. 

The last portions of water are removed from alcohol by allowing it to 
stand for two or three days over powdered quick-lime, and distilling, when 
the lime retains the water in the form of hydrate of lime, and the pure or 
absolute alcohol distils over. It must then be preserved in well stopped 
bottles, since it readily absorbs moisture from the atmosphere. Its attrac- 
tion for water causes it to evolve heat when mixed with that liquid, and 
the volume of the mixture is less than the sum of the volumes of its 
components, showing that combination has taken place. 

370. Ether, or, as it is sometimes erroneously called, sulphuric ether 
(C 4 H 10 0), is obtained by distilling a mixture of two measures of alcohol 
with one measure of concentrated sulphuric acid. As soon as the mixture 
begins to blacken, - in consequence of a secondary decomposition of the 
alcohol, the retort is allowed to cool, another half measure of alcohol is 
added, and the mixture again distilled as long as ether is obtained. 




Fig. 292. — Continuous etherification. 

A far better method of obtaining ether is that known as the continuous 
process. Alcohol of sp. gr. 0*830 is mixed with an equal measure of con- 
centrated sulphuric acid, and introduced into a retort or flask (fig. 292), 



PROPERTIES OF ETHER. 511 

which is connected with a small cistern containing alcohol. The mixture 
in the flask is rapidly raised to the boiling point, and alcohol is allowed to 
pass slowly in from the reservoir through a syphon furnished with a stop- 
cock, so as to keep the liquid in the flask at a constant level. A thermo- 
meter should be immersed in the liquid, the temperature of which should 
be maintained at .284° to 290° F. By this process, one measure of sul- 
phuric acid will effect the conversion into ether of thirty measures of 
alcohol. 

The boiling point of ether being very low (94 0, 8 F.) necessitates the 
employment of a good condensing arrangement in this process. 

The liquid which distils over contains about two-thirds of its weight 
of ether, with about one-sixth of water, and an equal quantity of alcohol. 
Traces of sulphurous acid are also generally present. To obtain the pure 
ether, it is shaken with water containing a little carbonate of potash, when 
the water dissolves the alcohol, and the potash removes the sulphurous 
acid ; the ether being very sparingly soluble in, and much lighter than 
water (sp. gr. 0*74), rises to the surface, holding a little water in solution. 
This upper layer is drawn off and freed from water by distillation in a 
water bath, at a very low heat, over quick-lime. 

The explanation of the chemistry of this process of etlierification will 
be more intelligible after some other changes to which alcohol is liable 
have been studied. 

The most striking properties of ether are its peculiar odour and its 
great volatility ; its rapid evaporation when poured upon the hand gives 
rise to a sensation of intense cold ; and if a little ether be evaporated by 
blowing upon it in a watch-glass with a drop of water hanging from its 
convexity, the water will be speedily frozen. Ether is also exceedingly 
inflammable ; and since its vapour is very heavy (sp. gr. 2 '59), and passes 
in an unbroken stream through the air for a considerable distance, great 
care should be taken to avoid pouring it from a bottle in the neighbour- 
hood of a flame. Its flame is far more luminous than that of alcohol, and 
much acetylene is produced during its imperfect combustion (p. 51). 

The high specific gravity, volatility, and inflammability of ether vapour admit of 
illustration by some curious experiments : — 

If a small piece of sponge be saturated with *ther and placed in the centre of a 
large wooden tray, two or three inches deep, the latter will soon be entirely filled 
with the vapour, as may be shown by applying a lighted match to one corner. A 
jug may be warmed by rinsing a little hot water round it, and this having been 
thrown out, a few drachms of ether may be poured into the jug, which will imme- 
diately become filled with ether vapour, and from this several glasses may be filled 
in succession, the presence of tlie ether vapour being proved by a lighted taper. 

A pneumatic trough may be filled with warm water, a small test-tube filled with 
ether inverted with its mouth under the water, and the ether quickly decanted up 
into a gas jar also filled with hot water, where it will be immediately converted into 
vapour, and may be decanted through the water into other vessels, and dealt with 
like a permanent gas. Some cold water poured over the jar containing it at once 
proves its condensible character. 

When ether is acted upon by hydrochloric, hydrobromic, or hydriodic 
acid, the oxygen of the ether enters into combination with the hydrogen 
of the acid, and the chlorine, bromine, or iodine occupies its place. 

Thus, with hydrochloric acid — 

(C 2 H 5 ) 2 {Ether) + 2HC1 = 2C 2 H 5 C1 {Hydrochloric ether) + H 2 . 

In a similar manner, hydrobromic ether, C 2 H 5 Br, and hydriodic ether, 



512 THE ALCOHOL-RADICALS. 

C 2 H 5 I, may be formed. The best method of obtaining the two last, how- 
ever, consists in distilling moderately strong alcohol with phosphorus, and 
either bromine or iodine, when phosphovinic or phosplietliylic acid and 
hydriodic ether are formed — 
12C 2 H 6 + P 2 + I 10 - 10C 2 H 5 I + 2H 2 0.(C 2 H 5 ) 2 O.P 2 O g + 4H 2 0.* 

Alcohol. Phosphovinic acid. 

These three ethers are colourless, fragrant, volatile liquids, which are 
of the greatest value in the investigation of the constitution of complex 
organic compounds. 

This remark applies particularly to hydriodic ether {iodide of ethyle), 
which is less volatile than the others, and therefore more easily manage- 
able in experiments requiring a high temperature. 

Iodide of ethyle, or ethylic iodide, is prepared by distilling 1400 grains of ordinary 
alcohol (sp. gr. 0"84) with 2000 grains of iodine, and 100 grains of ordinary vitreous 
phosphorus. The iodine and phosphorus are added alternately, in small portions, 
to the alcohol in the retort, which is immersed in cold water to moderate the action, 
and occasional^ shaken. When the whole has been added, the retort is connected 
with a Liebig's condenser, and heated in the water-bath, when about 2| measured 
ounces of iodide of ethyle mixed with alcohol will pass over. This is shaken in a 
stoppered bottle with about an equal measure of water, which dissolves the alcohol, 
leaving the iodide of ethyle to collect at the bottom as an oily layer (sp. gr. 1*97). 
After as much as possible of the upper aqueous layer has been removed with a 
siphon or pipette, the iodide is poured into a small retort containing fused chloride 
of calcium in powder to remove the water. The retort is closed with a cork, and set 
aside for some hours, when the iodide of ethyle may be distilled off in the water- 
bath, and condensed in a Liebig's condenser. 

371. Alcohol-radicals. — If ethylic iodide be poured over granulated 
zinc contained in a stout glass tube, which is then exhausted of air, 
hermetically sealed, and heated for two hours in an oil-bath to 300° F., 
a crystalline substance is deposited, which is a compound of iodide of 
zinc with zinc-ethyle (C 2 H 5 ) 2 Zn, whilst a colourless liquid separates, con- 
sisting of a mixture of three hydrocarbons, which have been liquefied by 
their own pressure. On breaking the extremity of the tube under water, 
this liquid rapidly escapes in the form of gas, which proves on examina- 
tion to contain olefiant gas (C 2 H 4 ), hydride of ethyle (C 2 H 6 ), and ethyle 
(C 2 H 5 ) 2 , the last of which may be obtained nearly pure by collecting the 
last portions of gas separately, since ethyle is the least volatile of these 
hydrocarbons. 

JSTeglecting the secondary decompositions which give rise to the other 
products, the formation of ethyle would be represented by the simple 
equation — 

2C 2 H 5 I + Zn - Znl 2 + (C,H 5 ) 2 

Ethylic iodide. Ethyle. 

Ethyle is a colourless gas, having a faint ethereal smell, insoluble in 
water, and requiring a pressure of two or three atmospheres for its lique- 
faction. The interest which attaches to it is due to its being regarded 
by many chemists as the radical or starting-point of the series of com- 
pounds derived from vinic alcohol, which is thence spoken of as the 
ethyle series, and this view of the constitution of those compounds was 
in favour long before the compound (C 2 H 5 ) 2 was obtained in the separate 
state, this being a discovery of recent date. 

* It will be seen that this change is precisely similar to that which occurs in the 
preparation of hydriodic acid by the simultaneous action of phosphorus and iodine upon 
water — 

12H.0 + P., + I 10 = 10 HI + 2H 3 O.H 2 O.P.A + 4H 2 . 



DUPLICATE NATURE OF THE ALCOHOL-RADICALS. 513 

Mention has already been made of the existence of another radical, 
methyle (CH 3 ) 2 , obtained by a similar process, which may be regarded as 
the starting-point of the wood-spirit series. 

Butyle (C 4 H 9 ) 2 , amyle (CgH,^, and caproyle (C 6 H 13 ) 2 the supposed radi- 
cals of the butylic, amylic, and caproic alcohols, have also been obtained, 
these being liquids with progressive boiling points. "We are thus in 
possession of several members of a homologous series of hydrocarbons, 
which may be designated the alcohol-radicals, and represented by the 
general formula (C M H 2re + x ) 2 . 

If a mixture of iodide of ethyle and iodide of amyle (C 5 H n I, prepared 
from fousel oil just as iodide of ethyle is from alcohol) be heated with 
sodium, a colourless liquid is obtained, which is a true combination of 
ethyle and amyle (C 2 H 5 .C 5 H n )— 

C 2 H 5 I + C 5 H n I + STa 2 = 2NaI .+ C 2 H 5 .C 5 H n . 

Iodide of Iodide of f+iwIp ™v1p 

ethyle. amyle. Ethyle-amyle. 

In a similar manner, ethyle-butyle (C 2 H 5 .C 4 H 9 ), methyle-caproyle 
(CH 3 .C 6 H 13 ), butyle amyle (C 4 H 9 .C 5 H n ), and butyle-caproyle (C 4 H 9 .C 6 H 13 ), 
have been obtained. 

These double radicals all yield two volumes of vapour for each mole- 
cule of the compound, showing that the empirical formula for methyle 
(CH 3 ), which furnishes only one volume, must be converted into that of 
a double radical, methyle-methyle (CH 3 .CH 3 ), which would give two 
volumes of vapour, and in a similar manner, ethyle would become 
(C 2 H 5 ,C 2 IL), butyle (C 4 H S ,C 4 H 9 ), and so on. 

This duplicate nature of the radicals at once explains the circumstance 
that they do not unite directly with chlorine, bromine, &c, as might have 
been expected. Thus ethyle, with iodine, does not combine to form 
iodide of ethyle, because the ethyle itself is an ethylide of ethyle. 

Again, the formation of zinc ethyle (C 2 H 5 ) 2 Zn, and of hydride of ethyle 
(C. 2 H 5 H), during the action of zinc upon iodide of ethyle, becomes 
intelligible upon this view. Indeed, the first stage of this action appears 
to consist in the formation of zinc-ethyle— 

2C 2 H 5 I + Zn 2 = (C 2 H 5 ) 2 Zn + Znl 2 . 

Iodide of ethyle. Zinc-ethyle. 

In the second stage, the zinc-ethyle acts upon a fresh portion of iodide 
of ethyle, producing iodide of zinc and the double radical ethyle — 

2C 2 H 5 I + (C 2 H 5 ) 2 Zn = Znl 2 + 2(C 2 H,C 2 H 5 ). 

'^/le?' Zinc-ethyle. 

The hydride of ethyle itself clearly corresponds to the double radical 
ethyle, one-half of which is replaced by an atom of hydrogen (C 2 H 5 .H). 

The simultaneous formation of hydride of ethyle and of olefiant gas 
during the action of zinc upon iodide of ethyle, might be represented by 
the equation — 

2C 2 H 5 I + Zn = Znl 2 + C 2 H 5 .H + C. 2 H 4 . 

Iodide of ethyle. Hydride of ethyle. 

Hydride of ethyle is the representative of a series of homologous hydro- 
carbons, of which the first member, the hydride of methyle (CH 3 .H), is 
identical with marsh-gas. 

The following table exhibits some of the chief members of the marsh- 

2 K 



514 HYDRIDES OF THE ALCOHOL-RADICALS. 

gas series of hydrocarbons (general formula C^H^+g), as well as the 
corresponding alcohol-radicals,* having the general formula 2(C„H 8b+1 ) — 





Radical. 


Hydride.T 


Methyle, 


CH3.CH3 


Cxi 3. H = CH. 4 


Ethyle, 


• • C 2 H 5 .C 2 H 5 


C 2 H 5 .H = C 2 H 6 


Butyle, 


. . C 4 H 9 .C 4 H9 


C 4 H 9 .H = C 4 H 10 


Amyle, 


• • CgHn.CgHji 


C 5 H n .H = C 5 H 12 



The three first of these hydrides are gaseous, the last a volatile liquid. 

If ethyle (C 2 H 5 ) 2 = E 2 he accepted as the radical of the alcohol series, 
then ether (C 2 H 5 ) 2 would become the oxide of ethyle, and alcohol 
(C 2 H 5 HO), the hydrate of ethyle ; and it will be seen that upon this 
view a considerable number of the relations of these bodies can be readily 
explained. 

372. On referring to the action of hydrochloric acid upon ether, it will 
be seen to resemble exactly that of the same acid upon the basic oxide of 
a metal, consisting in an exchange between the chlorine of the acid and 
the oxygen of the base. Chloride of ethyle may also be produced by the 
action of hydrochloric acid upon alcohol (EHO), just as chloride of 
potassium is produced by the action of that acid upon caustic potash — 

EHO (Alcohol) + HC1 = EC1 (Chloride of ethyle) + H 2 . 

It would be expected that the action of other acids upon alcohol would 
correspond to their action upon caustic potash, and with several acids this 
is really the case, although it is far more difficult to break up the alcohol 
than the caustic potash. 

If alcohol be boiled for many hours with dry oxalic acid (H 2 C 2 4 ) in 
a flask provided with a long tube, so that the volatilised alcohol may run 
back, it is found that, on diluting the solution with water, a heavy fra- 
grant liquid separates, which has the composition (C 2 H 5 ) 2 C 2 4 , and is 
termed oxalic ether. 

Its formation may be thus represented — 

2EHO + H 2 C 2 4 = E 2 C 2 4 + H 2 0. 

Alcohol. Oxalic acid. Oxalic ether. 

It is formed far more easily in the presence of strong sulphuric acid, since 
this developes ether (E 2 0) which is decomposed by the oxalic acid. 

By treatment with caustic potash, the oxalic ether is decomposed, 
yielding oxalate of potash and alcohol ; thus — 

E 2 C 2 4 + 2KHO = K 2 C 2 4 + 2EHO. 

But if oxalic ether be mixed with only half the quantity of caustic 
potash required for this decomposition, there is obtained, instead of oxalate 
of potash, a salt, crystallising in pearly scales, having the composition 
KEC 2 4 , the formation of which is easily understood — 

E 2 C 2 4 + KHO = KEC 2 4 + EHO. 

Oxalic ether. Oxalovinate of potash. 

By decomposing this salt with hydrofluo silicic acid (see p. 185) to remove 
the potassium in an insoluble form, a new acid is obtained, which has the 
composition HEC 2 4 , and is called oxalomnic or oxalethylic acid. It 

* See also American petroleum, p. 463. 

| Each of these hydrides is isomeric with the radical immediately preceding it. Thus 
hydride of ethyle has the same composition as methyle, and is regarded by some chemists 
as identical with it. 



ETHERS, 515 

might evidently be also called the binoxalate of ethyle, since it corre- 
sponds in composition to the binoxalate of potash, KHC 2 Q 4 . 

Most of the acids form ethers corresponding to oxalic ether ; thus, by 
distilling acetic acid with alcohol and sulphuric acid, and diluting the 
distilled liquid with water, acetic ether (EC 2 H 3 2 ) is separated, remark- 
able for its very fragrant odour, which has a share in the perfume of 
cider, perry, vinegar, and of many wines. 

The ether used in medicine under the names of sweet spirits of nitre, 
nitrous ether, and nitric ether, is essentially a solution of nitrous ether 
(C 2 H 5 )N0 2 in alcohol, and is formed when alcohol is distilled with nitric 
acid, when a violent and complicated reaction takes place, one portion of 
the alcohol being converted into aldehyde, at the expense of a part of the 
oxygen of the nitric acid — 

2(C 2 H 6 0) + HN0 3 - C 2 H 4 -1- G 2 H 5 K0 2 + 2H 2 0. 

Alcohol. Aldehyde. Nitrous ether. 

Mtrous ether is a very volatile liquid, characterised by a powerful 
odour of rennet-apples, and in the pure state decomposes spontaneously, 
evolving nitric oxide. 

True nitric ether (EN0 3 ) may also be obtained as a fragrant, heavy oily liquid, 
by distilling alcohol with nitric acid, under certain precautions. It is decomposed 
with explosion at a temperature of about 200° F. 

By the action of nascent hydrogen upon nitric ether, a basic substance is produced, 
which has been named hydroxylamine, in allusion to its remarkable formula, NH 3 0, 
which might be regarded as ammonia, NH 3 , in which one atom of hydrogen is re- 
placed by hydroxyle, HO — 

C 2 H 5 N0 3 + H 6 = C 2 H 5 HO + H 2 + NH 3 0. 

Nitric ether. Alcohol. ' Hydroxylamine. 

In order to obtain this base, 5 parts of nitric ether are acted on by 12 parts of tin 
and 50 parts of concentrated hydrochloric acid. "When the action is over, the alcohol 
is expelled by heat, the tin precipitated by hydrosulphuric acid, the solution evapo- 
rated to dryness, and the residue boiled with absolute alcohol, which leaves some 
hydrochlorate of ammonia undissolved. The hydrochlorate of hydroxylamine 
(NH 3 O.HCl) crystallises in long needles from the alcoholic solution. From the 
sulphate of hydroxylamine, by decomposition with baryta, a solution of the base 
itself may be obtained ; but pure hydroxylamine has not been isolated from the solu- 
tion, since it has a tendency to decompose into ammonia, water, and nitrogen — 

3NH 3 = NH 3 + N 2 + 3H 2 0. 
Hydroxyiamine. 

Hydroxylurea CH 3 (HQ)N 2 0, or urea in which hydrogen is replaced by hydroxyle, 
has also been obtained.. 

The chloric ether used for medicinal purposes is not an ether in the true sense of 
the term, but a solution of chloroform (CHC1 3 ) in alcohol. Chloroform will be more 
particularly described hereafter. 

Perchloric ether, (C 2 H 5 )C10 4 , is only interesting from the circumstance that, 
although an oily liquid, it explodes violently under a sudden blow. 

Boracic ether, which has the formula E 3 B0 3 , is formed when terchloride of boron 
is decomposed by alcohol — 

BC1 3 + 3(EHO) = E 3 B0 3 + 3HC1 , 

and may also be obtained by heating anhydrous boracic acid with an excess of 
alcohol under pressure. It is lighter than water (sp. gr. 0-88), and boils at 246° F. 
When heated with anhydrous boracic acid, it is converted into E 2 O.B 2 3 , which is 
decomposed by heat into E 3 B0 3 and E 2 0. 3B 2 3 , the latter being a vitreous solid. 

"When chloride of silicon is decomposed by alcohol, the compound 2E 2 O.Si0 2 is 
produced — 

SiCl 4 + 4(EHO) = 2E 2 O.Si0 2 {Silicic ether) + 4HC1. 

This silicic ether is a colourless liquid, of sp. gr. 0'93, and distilling unchanged at 



516 SULPHOVINIC ACID. 

330° F. It has an ethereal odour, and burns with a brilliant flame which deposits 
silica. "When poured upon the surface of water, it gradually decomposes, with 
separation of gelatinous hydrated silica — 

2E 2 O.Si0 2 + 2H 2 = 4(EHO) (Alcohol) + Si0 2 . 

"When the ether is kept in a moist atmosphere, it deposits a hard transparent mass 
of silica, known as artificial quartz. 

Two other silicic ethers have been obtained, having respectively the composition 
E 2 O.Si0 2 and E 2 0.2Si0 2 ; the former liquid, the latter viscous. 

Carbonic ether (E 2 O.C0 2 ) may be obtained by heating carbonate of silver with 
iodide of ethyle in a sealed tube ; 

Ag 2 O.C0 2 + 2EI = E 2 O.C0 2 + 2AgI . 

The compound 2E 2 O.C0 2 has been obtained by the action of sodium upon an alco- 
holic solution of chloropicrine — 

CC1 3 (N0 2 ) + 4(EHO) + Na 4 = 3NaCl + NaN0 2 + 2E 2 O.C0 2 + H 4 . 

„,. . . „ ,,„-„, Subcarfoonate of 

Chloropicrine. Alcohol. ethyle 

When carbonic acid is passed through a solution of hydrate of potash in absolute 
alcohol, the carbovinate of potash is obtained, in crystals having the composition 
KECO3, corresponding to bicarbonate of potash, KHC0 3 . 

Bytlie action of syrupy phosphoric acid upon alcohol, thecompound 2H 2 O.E 2 O.P 2 5 , 
phosphovinic acid, is formed, and by neutralising it with a base, a phosphovinate may 
be obtained, composed after the general formula 2M 2 'O.E 2 O.P 2 5 . 

A second acid is formed at. the same time, having the formula H 2 0.2E 2 O.P 2 5 , its 
salts being M 2 '0.2E 2 O.P0 5 . Phosphovinic acid is found abundantly in the residue 
from the preparation of iodide of ethyle. 

The true phosphoric ether (3E 2 O.P 2 5 ) is also said to have been obtained. 

The true sulphuric ether (E 2 O.S0 3 ) can only be formed by passing the vapour of 
anhydrous sulphuric acid into ether. It is an oily liquid, heavier than water, and 
decomposed by heat, defiant gas and alcohol being found amongst the products, for 
C 2 H 4 + C 2 H 6 = (C 2 H 5 ) 2 0. 

The fragrant liquid known as heavy oil of wine, which is formed towards the latter 
part of the preparation of ether and of olefiant gas (page 92), appears to contain 
the sulphate of oxide of ethyle, together with some hydrocarbons of the olefiant gas 
series. When decomposed with a solution of potash, light oil of wine rises, which 
contains hydrocarbons of the olefiant gas series. 

373. When ether or alcohol is added to concentrated sulphuric acid, 
much heat is evolved, in consequence of the combination of the oxide of 
ethyle with sulphuric acid, to form sulphovinic or sulphethylic acid, 
H 2 O.E 2 0.2S0 3 or bisulphate of oxide of ethyle, corresponding in com- 
position to the bisulphate of potash, K 2 O.H 2 0.2S0 3 . If baryta be now- 
added to the solution, the uncombined sulphuric acid will be precipitated 
in the form of sulphate of baryta, but the sulphovinic acid will combine 
with the base to form the sulphovinate of baryta, which may be obtained 
by evaporating the solution, in rhombic prisms which have the formula 
BaO.E 2 0.2S0 3 .2Aq., and are easily soluble in water. By cautiously 
adding sulphuric acid to the solution of sulphovinate of baryta till the 
whole of the baryta is precipitated as sulphate, and evaporating the filtered 
liquid in vacuo, the pure sulphovinic acid is obtained as a syrupy liquid 
liable to spontaneous decomposition, and readily decomposed when heated 
with water, into alcohol and sulphuric acid — 

H 2 O.E,0.2S0 3 + 2H 2 - 2(H 2 O.S0 3 ) + 2EHO. 

Sulphovinic acid. Alcohol. 

The sulphovinate of soda, prepared by decomposing the baryta-salt 
with carbonate of soda, is used medicinally in Germany. 

374. Vinic acids are not formed by monobasic acids. — It must be noticed 
that although the greater number of the acids are capable of forming ethers, 



THEORY OF FORMATION OF ETHER. 517 

only a few of them produce vinic acids. Indeed, only those acids form 
vinic acids which are polybasic, i.e., require more than one atom of a 
metal for the formation of a normal salt (p. 254), the tendency to form a 
vinic acid depending upon the possibility of replacing a portion of the 
hydrogen in the hydrated acid by ethyle. In the case of nitric acid, which 
is undoubtedly a monobasic acid, and does not form acid salts, no vinic 
acid can be produced ■ the formula of the acid being HN0 3 , the hydrogen 
must be entirely or not at all replaced by the ethyle. 

375. Theory of etherification. — When sulphovinic acid is decomposed 
by heat, especially in the presence of excess of alcohol, a large proportion 
of ether is found among the products, and this has given rise to a very 
general opinion among chemists, that the production of sulphovinic acid is 
an intermediate stage in the formation of ether, by the ordinary process 
of distilling alcohol with sulphuric acid. At first sight it would appear 
that the etherification of alcohol in this process was sufficiently explained 
by reference to the attraction of sulphuric acid for water, and consisted in 
a simple removal of water from the alcohol by the acid, for — 

2C 2 H fi O - H 2 = C 4 H 10 O. 

Alcohol. Ether. 

When it is found, however, that a continuous stream of alcohol, flowing 
into heated sulphuric acid in a retort, is converted into ether and water, 
which is not retained by the sulphuric acid, but distils over with the 
ether, and that this may go on almost without limit, this explanation is 
no longer tenable. 

Accordingly, the formation of ether from alcohol by the action of sul- 
phuric acid is generally referred to the formation of sulphovinic acid, as 
soon as the alcohol and the acid are brought in contact, and the subsequent 
decomposition of this sulphovinic acid, in the presence of water or alcohol, 
into hydrated sulphuric acid, water, and ether ; thus — 



H. 2 O.E 2 0.2S0 3 + H 2 = 

Sulphovinic acid. 


= 2(H 2 O.S0 3 ) + 


E 2 0, 

Ether. 


H 2 O.E 2 0.2S0 3 + 2EHO = 

Sulphovinic acid. Alcohol. 


- 2(H 2 O.S0 3 ) + 


2E 2 0. 

Ether. 



The hydrated sulphuric acid thus set free would of course give rise to 
the formation of a fresh quantity of sulphovinic acid, which would be 
decomposed in its turn, and so on without limit. 

A strong argument in favour of this view is deducible from the follow- 
ing experiment : — 

When amylic alcohol (the amylic hydrate C 5 H n HO) is mixed with con- 
centrated sulphuric acid, it forms sulphamylic acid (C 5 H n ) 2 O.H 2 0.2S0 3 , 
corresponding to sulphovinic acid, and if this be heated in a retort, and 
alcohol be allowed to flow into it, as in making ether, the first portion which 
distils over is found to be a true double ether molecule (C 2 H 5 .C-H u .O), the 
production of which would be represented by the equation — 

H 2 0.(C 5 H n ) 2 0.2S0 3 4- 2C 2 H 5 HO = 2(C 2 H 5 .C 5 H n .O) + 2(H 2 O.S0 3 ). 

Sulphamylic acid. Alcohol. Amylethylic ether. 

On continuing the distillation, nothing but ordinary ethylic ether is 
obtained. 

The existence of these double ethers might have been anticipated from 
what has been said with respect to the double radicals (p. 513), but the 



518 CONSTITUTION OF ALCOHOL AND ETHEK. 

mode of formation in the above instance certainly affords support to the 
view, that ether results from the decomposition of sulphovinic acid by 
alcohol in the ordinary etherifying process. 

On the other hand, this theory of etherification is shaken by the circum- 
stance, that if vapour of alcohol be passed into boiling sulphuric acid, 
of sp. gr. 1*52 (boiling at 290°) almost the whole of the alcohol is resolved 
into water and ether, which distil over, so that either no sulphovinic acid 
is formed, or it is only formed to be immediately decomposed. If the acid 
have the sp. gr. 1*61 (boiling at 330°), no ether is obtained, the alcohol 
being resolved into olefiant gas and water. 

Moreover, hydrated phosphoric acid cannot be substituted for the sul- 
phuric acid in the preparation of ether, notwithstanding that it also forms 
a vinic acid. 

Hence, many chemists are inclined to attribute to sulphuric acid a 
specific action by contact {catalytic action) upon alcohol, causing its resolu- 
tion into water and ether, or olefiant gas, according to the temperature. 

This view receives some confirmation from the behaviour of sulphuric 
acid towards cellulose and certain other substances, in which it causes 
important transformations, without itself appearing to take part in the 
change. 

In connection with this subject, it is remarkably interesting to observe, 
that alcohol may actually be reproduced from olefiant gas and water under 
the influence of sulphuric acid. If concentrated sulphuric acid be vio- 
lently agitated in a vessel containing olefiant gas, the latter is absorbed, 
and on diluting the acid with water and distilling, a quantity of alcohol 
is obtained. 

376. Alcohols and ethers referred to the loater-type.— When potassium 
or sodium is thrown into absolute alcohol, the metal is dissolved with 
disengagement of heat and rapid evolution of hydrogen, and a crystalline 
compound is formed, known as potassium- alcohol (ethylate of potash) or 
sodium-alcohol (ethylate of soda), and containing an atom of the metal 
in the place of an atom of hydrogen ; the action of potassium upon 
alcohol would be thus represented — 

C 2 H 5 HO (Alcohol) + K = C 2 H 5 KO (Potassium-alcohol) + H . 

Other alcohols behave in a similar manner. ISTo one can fail to be struck 
with the similarity which exists between the action of potassium upon 
alcohol and upon water, and chemists have naturally endeavoured to refer 
both actions to a common type. 

The decomposition of water by potassium is represented by the 
equation — 

!}° + k = h} + h - 

Alcohol may be represented with equal fitness, as water in which half 
the- hydrogen is replaced by ethyle (C 2 H 5 ), or EHO, and the action of 
potassium upon it may be thus expressed — 



}0 + K = !}0 



H ^ 



Fotassium- 
alcohol. 



MERCAPTAN. 519 

In a similar manner sodium-alcohol would be formed.* 
When sodium-alcohol is heated in a sealed tube with the iodide of one 
of the alcohol-radicals, the sodium combines with the iodine, whilst the 
alcohol-radical enters into the place of the sodium, and a double ether is 
formed. 

Thus, if iodide of methyle (CH 3 I) be decomposed by sodium-alcohol — 

ch 3 i + £ a }o = mi + * H Jo. 

Sodium-alcohol. Methyl-ethylic 

ether. 

In a similar manner amyl-ethylic ether, q jj fO, would be produced. 

Again, if iodide of ethyle be decomposed by sodium-alcohol, common 
ether is obtained, and the action must in consistency be similarly ex- 
plained — 

C A I + C A}0 = Nal + gg} . 

Sodium-alcohol. Common ether. 

Alcohol and ether are constituted upon the same type, that of a mole- 
cule of water, and bear to each other the same relation as exists between 
caustic potash and potash ; thus — 



Potassium series. 




Ethyle series. 


Potassium, 


K 2 


(C 2 H 5 ) 2 Ethyle. 


Caustic potash, 


if° 


°A 1 Alcohol 


Potash, 


!}o 


^ 5 1 Ether. 



377. Compounds have been obtained corresponding to alcohol and ether, in which 
the place of the oxygen is occupied by sulphur, and which bear the same relation to 
hydrosulphuric acid as alcohol and ether bear to water. 

H ) 

Type. — Hydrosulphuric acid, tt J S 

Mercaptan, . ■ 2 jt s V S Hydrosulphate of potassium, ^ j S . 

All these compounds are distinguished for their powerful odour of garlic. This 
is especially the case with mercaptan, which is notoriously one of the most evil- 
smelling chemical compounds. It is prepared by distilling solution of hydrosulphate 
of potassium (obtained by saturating potash with hydrosulphuric acid) with sulpho- 
vinate of potash, or better, of lime — 

KC 2 H 5 S0 4 + | J S - C A j S + K 2 S0 4 . 
Sulphovinate of potash. Mercaptan. 

Mercaptan is a light, very volatile and: inflammable liquid, sparingly soluble in 
water. That it is constituted after the type of hydrosulphuric acid is shown by its 
action upon metals and their oxides. Potassium acts upon it precisely as it does 
upon alcohol — 



H 



+ K = C 2£ 5 JS + H 



Mercaptan Mercaptide of potassium 

mercaptan Qr potassiura . merca pt a n. 

* Thallium-alcohol, C 2 H 5 T10, has also been obtained as a colourless liquid remarkable 
for its high specific gravity (3-55) and great refractive and dispersive action upon light. 



520 CYANIDES OF ALCOHOL-RADICALS. 

Its name was bestowed in allusion to its action upon mercuric oxide, when it 
forms a white crystalline inodorous compound, insoluble in water but soluble in 
alcohol — 

2(C 2 H 5 )HS + Hg"0 = (C 2 H 5 .) 2 S.Hg"S + H 2 . 
Mercaptan. Mercaptide of mercury. 

378. Hydrocyanic ether (C 2 H 5 .CN = ECy), or cyanide of ethyle, is obtained by 
distilling sulphovinate of potash with cyanide of potassium — 

KESO4 + KCy = ECy + K 2 S0 4 . 

Sulphovinate Hydi-ocyanic 

of potash. * ether. 

The cyanide of ethyle is a volatile poisonous liquid, smelling strongly of garlic. 
Its most interesting feature is, that when boiled with a solution of potash, it furnishes 
propylate of potash, whilst ammonia is evolved — 

C 2 H 5 .CN + KHO + H 2 = KC 3 H 5 2 + NH 3 . 

Hydrocyanic Propylate of 

ether. potash. 

In a similar manner, the cyanides of all the alcohol-radicals, when boiled with 
solution of potash, yield the potash-salt of the acid which stands next in the 
homologous series. Thus cyanide of methyle (CH3.CN) yields the potash-salt of 
acetic acid belonging to the ethyle series ; cyanide of amyle (C 5 H n .CN) yields 
caproate of potash belonging to the caproyle series, and so on. This mode of decom- 
position argues strongly that hydrogen is really the type of these radicals, for when 
hydrocyanic acid (HON) is boiled with solution of potash, it yields the potash-salt 
of formic acid, the lowest member of the homologous series — 

HCN + KHO + H 2 = KCH0 2 + NH 3 . 

Hydrocyanic acid. Formiate of potash. 



Thus, leaving the potash out of consideration ; 



H.CN + 2H 2 = CH 2 2 + NH 3 

Cyanide of hydrogen. Formic acid. 

CH 3 .CN + 2H 2 = C 2 H 4 2 + NH 3 

Cyanide of methyle. Acetic acid. 

C 2 H 5 .CN + 2H 2 = C 3 H 6 2 + NH 3 . 
Cyanide of ethyle. Propylic acid. 

A plausible explanation of these changes may be given, if the hydrocyanic acid 
(HCN) be represented as ammonia (NH 3 ), in which two atoms of hydrogen are 
replaced by an atom of carbon (just as two atoms of hydrogen in water are replaced 
by one atom of carbon to form carbonic oxide) . 



* ( C" + H 2 j °2 


= g?J0 3 + NJH 


Hydrocyanic acid. Water. 


Formic acid. Ammonia. 


■ j<gP* + £|* 


~< CB ^jO a + HJH. 


Cyanide of methyle. 


Acetic acid. 


N j^)' + H : |0 2 


_ (C S H B )'H| N jH 

C" \ U2 + ^ j H 2 


Cyanide of ethyle. 


Propylic acid. 



The cyanides of the alcohol-radicals will be again referred to under their other 
designation of nitriles. 



ARSENICAL ALCOHOL OR ALCARSIN. 521 



KAKODYLE SEKIES— OKGANO-METALLIC BODIES. 

379. One of the most pleasing results of the progress of investigation 
in chemistry, is the discovery of the true position among classified com- 
pounds which is to be assigned to some substance hitherto regarded as 
anomalous, and as destroying by its presence the symmetry and complete- 
ness of an otherwise perfect classification. Such was the case, until 
within the last few years, with kakodyle, and the bodies derived from it. 
Discovered long before the science of organic chemistry was prepared to 
receive it, it taxed the ingenuity of chemists to find a place for it in their 
arrangement of organic compounds, and always occupied an anomalous 
and isolated position. Modern research has now brought to light a whole 
series of compounds, which would not have been complete without kako- 
dyle, and this hitherto incomprehensible substance has at length been 
assigned its proper place. 

When a mixture of equal weights of arsenious acid and dry acetate of 
potash is submitted to distillation, a heavy poisonous liquid is obtained, 
which has a most disgusting odour of garlic, and takes fire spontaneously 
when exposed to the air. This liquid, which has long been known under 
the names of alcarsin (arsenical alcohol), and Cadet 's fuming liquor, has 
the composition C 4 H 12 As 2 0, and its production may be represented (if the 
various secondary products be neglected) by the equation — 

4(KC 2 H 3 0. 2 ) + As 2 3 = C 4 H 12 As 2 + 2(K 2 O.C0 2 ) + 2C0 2 . 

Acetate of potash. Alcarsin. 

If acetic acid be represented by the formula derived above (p. 520) from its 
formation in the action of water upon cyanide of methyle, the formation of alcarsin 
would be easily explained. Acetate of potash would then be represented by the 

formula ^ 3 ' -, f 2 , and its action upon arsenious acid might be thus ex- 
pressed — 

As 2 j° 2 „+ 4^ CH 3^Jo 2 N ) M As, | ( cH,/ 4 + 2 ( K 2°- C °2) + 2C0 2 . 

Arsenious acid. Acetate of potash. Alcarsin. 

Alcarsin has the properties of a base ', it is capable of combining with 
the oxygen acids to form crystallisable salts, and in contact with the 
hydrogen acids it furnishes water, together with a salt of the radical of the 
acid. Thus, with hydrochloric acid, we have — 

C 4 H 12 As 2 + 2HC1 - C 4 H 12 As 2 Cl 2 + H 2 0. 

Alcarsin. Chloride. 

The best method of obtaining this chloride consists in dissolving the alcarsin 
in alcohol, and adding an alcoholic solution of corrosive sublimate, when 
a white crystalline solid is obtained, composed of C 4 H 12 As 2 O.HgCl 2 ; and 
on distilling this with hydrochloric acid (out of contact with air), another 
spontaneously inflammable liquid is obtained, of insupportable odour, and 
composed of C 2 H 6 AsCl. By distilling this chloride with zinc in an atmo- 
sphere of carbonic acid gas, a third unbearable liquid is procured, which 
has the formula C 4 H 12 As 2 , and has been named kakodyle, in allusion to 
its intolerable odour (/ax/cdg, bad). This substance is obviously the radical 
from which the compounds just mentioned are immediately derived ; thus — 



522 KAKODYLE SERIES. 

Kakodyle, C 4 H 12 As 2 = Kd 2 

Alcarsin, or oxide of kakodyle, C 4 H 12 As 2 = Kd 2 

Chloride of kakodyle, C 2 H 6 AsCl = KdCl . 

The remarkable properties of kakodyle leave no doubt as to its being 
really the radical of these compounds, in the same sense in which potas- 
sium is the radical of the oxide and chloride of that metal, for kakodyle 
enters into direct combination with chlorine and with oxygen, its attraction 
for the latter being so energetic as to cause its spontaneous inflammation 
in the air. 

The discovery of this radical, comporting itself in all respects like a 
metal, was of the utmost importance in its effect upon organic chemistry, 
affording very strong ground for belief in the existence of other quasi- 
metallic radicals, such as ethyle, methyle, &c, which have only recently 
been isolated. A similar service had been previously rendered to the 
science by the discovery of the compound radical cyanogen (CN) belong- 
ing to the electro-negative class opposed to the metals, and for a long time 
these two remained the only compound radicals which had been obtained 
in a separate form. 

When kakodyle is brought gradually in contact with oxygen, it is first 
converted into the oxide of kakodyle ((C 2 H 6 As) 2 0), and subsequently, if 
water be present, into kakodylic acid (HC 2 H 6 As0 2 = HKd0 2 ), which forms 
prismatic crystals, unaltered by air, aud destitute of poisonous character. 
When treated with hydrochloric or hydrosulphuric acid, it yields ter- 
chloride (KdCl 3 ) and sesquisulphide of kakodyle (Kd 2 S 3 ). 

The most poisonous member of this series is the cyanide of kakodyle 
(C 2 H 6 As.CN = KdCy), which is easily obtained in crystals by decom- 
posing cyanide of mercury in solution with oxide of kakodyle — 

HgCy 2 + Kd 2 = HgO + 2KdCy. 

A very minute quantity of this substance diffused in vapour through the 
air has the most dangerous effect upon those inhaling it. 

The following are the most important members of the kakodyle series — 

Kakodyle, (C 2 H 6 As) 2 = Kd 2 

Oxide of kakodyle, (C 2 H 6 As) 2 = Kd 2 

Sulphate of kakodyle, (C 2 H 6 As) 2 0. S0 3 = Kd 2 0. S0 3 

Sulphide of kakodyle, (C 2 H 6 As) 2 S = Kd 2 S 

Chloride of kakodyle, C 2 H 6 AsCl = KdCl 

Kakodylic acid, HC 2 H 6 As0 2 = HKd0 2 

Kakodylate of silver, AgC 2 H 6 As0 2 = AgKd0 2 

Sesquisulphide of kakodyle, (C 2 H 6 As) 2 S 3 = Kd 2 S 3 

Terchloride of kakodyle, C 2 H 6 AsCl 3 = KdCl 3 . 

380. Organo-metallic compounds. — The only way of referring kakodyle 
to any known series was to regard it as an association of arsenic with two 
molecules of methyle (CH 3 ), and this supposition necessitated the exist- 
ence of other compounds of a similar nature, formed, that is, hj the asso- 
ciation of an inorganic element with a quasi-metallic radical. Accordingly, 
within the last few years, it has been discovered that by heating the 
iodides of methyle, ethyle, and amyle, with zinc, compounds of those 
radicals with the metal can be obtained, and these compounds, like kako- 
dyle, are distinguished by their remarkable attraction for oxygen. 

Nor are arsenic and zinc the only elements with which these radicals 



PREPARATION OF ZINC-ETHYLE. 



523 



can be associated; boron, potassium, sodium, magnesium, aluminum, 
cadmium, tin, antimony, bismuth, lead, and mercury may be made to 
furnish similar compounds, and the principle is now fully established 
that the alcohol-radicals can enter into combination with metals to form 
compounds which are, in some cases, capable of direct union with oxygen 
and other electro-negative elements, for which they exhibit a greater 
attraction than the metals themselves. 

The members of this class of organo-metdllic bodies which have been 
the subjects of some of the most important researches deserve special 
attention. 

Zinc-ethyle is prepared by the action of zinc upon iodide of ethyle — 



2C 2 H 5 I + Zn 2 



(C 2 H 5 ) 2 Zn + Znl 2 



800 grains of bright freshly granulated and thoroughly dried zinc are placed in a 
half-pint flask (E, fig. 293), which is connected with -the carbonic acid apparatus (A), 




Fig. 293. — Preparation of zinc-ethyle. 

from which the gas is passed through strong sulphuric acid in the bottles (B and C) 
where it is thoroughly dried. A second perforation in the cork of the flask (E) allows 
the passage of the tube /, which passes through the two corks in the wide tube F, and 
dips into a little mercury in D. A stream of cold water is kept running through 
the wide tube (F), being conveyed by the caoutchouc tubes t t. When the whole 
apparatus has been filled with carbonic acid, the cork of the flask (E) is removed, and 
400 grains of iodide of ethyle (perfectly free from moisture) are introduced, the cork 
being then replaced.* The carbonic acid is again passed for a short time, and then 
cut off by closing the nipper-tap (T) upon a caoutchouc connector, when the gas 
escapes through the tube (G-), which dips into mercury, A gentle heat is then applied 
by a water-bath to the flask (E) till the iodide of ethyle boils briskly, the vapour 
being condensed in the tube/, and running back into the flask. In about five hours 
the conversion is complete, and the iodide ceases to distil. The nipper-tap (T) is 
again opened and a slow current of carbonic acid allowed to pass ; the position of 
the condenser (F) is reversed (fig. 294), and the tube /is connected, by the cork K, 
with the short test-tube ; the longer limb of a very narrow siphon (I) of stout 
tube passes through a second perforation in the cork (K), the shorter limb passing 
into the very short test-tube (P), the cork of which is also furnished with the short 
piece of moderately wide tube (L). For receiving and preserving the zinc-ethyle, a 
number of small tubes are prepared of the form shown in fig. 295. The long narrow 
neck (E) of one of these is passed down the short tube (L) to the bottom of P, the 
other end (N) of the tube being connected with an apparatus for passing dry car- 

* The process is said to be much accelerated if about -roth of zinc-ethyle is dissolved in 
the iodide of ethyle. 



524 ZINC-ETHYLE — ZINC-METHYLE. 

bonic acid. The whole of the apparatus being filled with this gas, the nipper-tap is 
closed, and the flask (E) heated on a sand-bath, so that the zinc-ethyle may distil 
over, a slow stream of carbonic acid being constantly passed into P, the excess 





Fig. 294. — Collection of zinc-ethyle. 

escaping through L. When enough zinc-ethyle has collected in the tube (0) a 
blow-pipe flame is applied to the narrow tube (N), which is drawn off and sealed ; 

the syphon tube (1) is then gra- 
dually pushed down, so that its 
longer limb may be sufficiently 
immersed in the zinc-ethyle, and. 
the nipper-tap (T, fig. 293) is 
Fig. 295. opened, when the pressure of the 

carbonic acid forces over a part 
of the zinc-ethyle into the tube P. By heating the tube (M) with a spirit-lamp, so 
as to expel part of the carbonic acid, and allowing it to cool, it will become partly 
filled with zinc-ethyle, and may be withdrawn and quickly sealed by the blow-pipe. 
The spontaneous inflammability of the zinc-ethyle, and its easy decomposition by 
water, render great care necessary in its preparation. If an alloy of zinc with one- 
fourth its weight of sodium be employed, the conversion may be effected in an hour. 

If any moisture were present in the materials employed, it would 
decompose a corresponding quantity of the zinc-ethyle, yielding oxide of 
zinc and gaseous hydride of ethyle — 

(C 2 H 5 ) 2 Zn + H 2 = 2(C 2 H 5 .H) + ZnO . 

Zinc-ethyle. Hydride of ethyle. 

Zinc-ethyle is a colourless' liquid of powerful odour, heavier than water 
(sp. gr. 1'18), and boiling at 244° IT. In contact with atmospheric air, 
it takes fire spontaneously, burning with a dazzling greenish-blue flame, 
which emits white clouds of oxide of zinc. If a piece of porcelain be 
depressed upon the flame, a deposit of metallic zinc is formed, surrounded 
by a ring of oxide, which is yellow while hot, and white on cooling. 

When oxygen is allowed to act very gradually upon zinc-ethyle, zinc- 
alcohol (or ethylate of zinc) is formed, corresponding to potassium- and 
sodium-alcohol (ethylates of potash and soda), which have been already 
described — 

(C 2 H 5 ) 2 Zn + 2 = Zn(C 2 H 5 ) 2 2 . 

Zinc-alcohol. 

Under the gradual action of other electro-negative elements, zinc-ethyle 
is decomposed into compounds of zinc and ethyle with the particular 
element employed ; (C 2 H 5 ) 2 Zn + I 4 = 2C 2 H 5 I + Znl 2 . 

Zinc-methyle (CH 3 ) 2 Zn is prepared by the action of zinc upon the iodide 
of methyle (CH 3 I), and resembles zinc-ethyle in its general character ; it 
is, however, far more volatile and more energetic in its reactions than 



ARSENIO-TRIMETHYLE ARSENIO-TRIETHYLE. 525 

zinc-ethyle, and is decomposed with inflammation and explosion when 
"brought in contact with water, yielding oxide of zinc and marsh-gas 
(hydride of methyle). 

(CH 3 ) 2 Zn + H 2 = 2(CH 3 .H) (Hydride of methyle.^ + ZnO . 

Zinc-amyle (C 5 H n ) 2 Zn is not so violent in its reactions ; it does not 
inflame when exposed to air, but absorbs oxygen very rapidly. 

Potassium-ethyle and sodium-ethyle (C 2 H 5 .K and C 2 H 5 .^Na) have as 
yet been obtained only in combination with zinc-ethyle by heating this 
liquid in a sealed tube with potassium or sodium, when metallic zinc is 
separated, and the alkali-metal takes its place — 

3(C 2 H 5 ) 2 Zn + Nn, = 2(Zn(C 2 H 5 ),NaC 2 H 5 ) + Zd . 

The double compound of sodium-ethyle with zinc-ethyle is a crystalline 
solid which decomposes water with great violence, forming soda, oxide 
of zinc, and hydride of ethyle.* Its behaviour with carbonic acid is very 
interesting and important. 

When the crystalline compound of sodium-ethyle with zinc-ethyle is 
introduced into a bulb-tube through which dry carbonic acid gas is 
passed, much heat is evolved, zinc-ethyle distils off, and a white solid is 
left in the bulb, which is found to consist of the propylate of soda, 
N"aC d H 5 2 formed according to the equation — 

C 2 H 5 l\ T a + C0 2 = NaC 3 H 5 2 . 

This reaction is one of very great importance, representing the first 
successful attempt to produce directly one of the organic acids from 
carbonic acid, and indicating a general method for the formation of the 
other acids of the same series. 

Thus, if sodium-methyle be treated in the same way, it yields acetate 
of soda — 

CH 8 ffa + C0 2 = NaC 2 H 3 2 . 

By heating iodide of methyle in a sealed tube with a compound of 
arsenic and sodium, kakodyle or arsenio-dimeihyle is obtained — 

2 CH 3 .I) + As^a 2 = As(CH 3 )^ + 2Nal , 

Kakodyle. 

and thus kakodyle finds its place among the organo-metallic bodies, 
the existence of which it foreshadowed. 

When iodide of ethyle is treated in a similar manner, arsenio- 
diethyle, As(C 2 H 5 ) 2 , or ethylic kakodyle, is obtained. 

381. Arsenio-trimetliyle or trlmethylarsine, As(CH 3 ) 3 , and arsenio- 
trietliyle or triethylarsine, As(C 2 H 5 )„ may be obtained either by acting 
upon the iodides of methyle and ethyle with a compound of arsenic with 
three atoms of sodium — 

3(CH,.I) + AsNa 3 - As(CH 3 ) 3 + 3^TaI, 

or by decomposing zinc-methyle or zinc-ethyle with terchloride of 
arsenic — 

3Zn(C 2 H 5 ) 2 + 2AsCl 3 = 2As(C 2 H 5 ) 3 + 3ZnCl 2 . 

Arsenio-triethyle has a kakodylic odour, but does not take fire when ex- 

* Strange to say when this compound of sodium-ethyle with zinc-ethyle is heated, it 
leaves metallic sodium and zinc. 



526 ALUMINUM ETHIDE — TRIBORETHYLE. 

posed to air, although it oxidises with, great rapidity. Like kakodyle, it 
is capable of producing a base by combination with oxygen, which has 
the formula As(C 2 H 5 ) 3 0, and is called arsenic triethoxide. Similar com- 
pounds have been obtained in which the oxygen is replaced by chlorine, 
iodine, and sulphur. 

Other arsenical compounds of ethyle and methyle have been produced, 
containing four equivalents of the alcohol-radical, but the oxide of tetre- 
thyl-arsonium [As(C 2 H 5 ) 4 ] 2 and its congeners are really substances be- 
longing to the ammonium family, and they will be again alluded to 
elsewhere. 

Stibethyle, Sb(C 2 H 5 ) 3 , or stibiotriethyle, and stibiotrimethyle, Sb(CH 3 ) 3 , 
are obtained by processes similar to those which furnish the correspond- 
ing compounds of arsenic, which they much resemble. 

Stibethyle has a powerful odour of onions, and takes fire spontaneously 
in air. It combines with oxygen, chlorine, iodine, and sulphur, with 
great energy. So powerful is its attraction for chlorine, that it displaces 
hydrogen from concentrated hydrochloric acid — 

Sb(C 2 H 5 ) 3 + 2HC1 = Sb(C 2 H 5 ) 3 .Cl 2 + H 2 . 

Bichloride of stibethyle. 

The oxide of stibethyle is a basic substance. The iodide of tetre- 
thylstibonium, Sb(C 2 H 5 ) 4 I, belongs to the ammonium family. 

Mercuric methide Hg(CH 3 ) 2 and ethide Hg(C 2 H 5 ) 2 are formed by the 
action of zinc-methyle and zinc-ethyle upon bichloride of mercury — 

Zn(C 2 H 5 ) 2 + HgCl 2 = ZnCl 2 + Hg(C 2 H 6 ) 2 . 

The methyle compound is the heaviest liquid (except metallic mercury) 
which is known; its specific gravity is 3*07, so that glass floats upon its 
surface. 

Aluminum ethide, A1 2 (C 2 H 5 ) 6 , is obtained by decomposing mercuric 
ethide with aluminum, 3HgE 2 + Al 2 == Hg 3 + A1 2 E 6 . It is a colour- 
less liquid, spontaneously inflammable, and decomposed by water. The 
corresponding methyle compound, A1 2 (CH 3 ) 6 , solidifies at a little above 
32° E. into a transparent crystalline mass. 

Tribor ethyle B(C 2 H 5 ) 3 , has been obtained by the action of zinc-ethyle 
upon boracic ether — 

2E 3 B0 3 + 3ZnE 2 = 2BE 3 + 3ZnE 2 2 . 

Boracic ether. Zinc-ethyle. Triborethyle. Ethylate of zinc. 

It distils over as a very light (sp. gr. 0*69) colourless liquid which has 
an irritating odour, and is insoluble in water. It inflames spontaneously 
in air, burning with a beautiful green flame, and explodes when brought 
in contact with pure oxygen. By gradual oxidation it is converted into 
the compound BE 3 2 , which may be distilled in vacuo without decom- 
position. When this liquid is mixed with water it is decomposed, yield- 
ing alcohol, and a volatile white crystalline body, BH 2 E0 2 — 

BE 3 2 + 2H 2 = BH 2 E0 2 + 2(EHO) . 

Alcohol. 

This substance has an agreeable odour, and a most intensely sweet 
taste ; it is very soluble in water, alcohol, and ether. 

Boric methide, B(CH 3 ) 3 , is formed by the action of a strong ethereal 
solution of zinc-methyle upon boracic ether — 

2E 3 B0 3 + 3ZnMe 2 = 2BMe 3 + 3ZnE 2 2 . 

Zinc-methyle. Boric methide. Ethylate of zinc. 



BORIC METHIDE — SILICIUM-ETHYLE. 



527 



Boric methide is a heavy (sp. gr. 1*93) colourless gas, having an intoler- 
ably pungent tear-exciting odour, and capable of liquefaction under a 
pressure of three atmospheres at 50° F. When it issues very slowly into 
the air from a tube, it undergoes partial oxidation, and produces a lam- 
bent blue flame, invisible in daylight, and incapable of burning the 
fingers ; but when it comes rapidly into contact with air, it burns with a 
bright green hot flame, remarkable for the immense quantity of large 
flakes of carbon which it disperses through the air, apparently because 
the boracic acid produced envelopes them and prevents their combustion. 
Boric methide combines with an equal volume of ammonia gas, producing 
a white, volatile compound NH 3 .BMe 3 , which is deposited in fine crystals 
from its ethereal solution, and may be sublimed without decomposition. 
Its vapour, like that of sal-ammoniac, occupies four volumes instead of 
two. Water absorbs very little boric methide, but alcohol dissolves it 
readily. Solutions of the alkalies and alkaline earths also absorb it, and 
potash decomposes the ammonia compound, but the combinations of boric 
methide with the alkalies do not crystallise, and are decomposed even by 
carbonic acid. 

Silicium-ethyle, SiE 4 , results from the decomposition of chloride of 
silicon with zinc-ethyle ; it is not decomposed by water or by solution of 
potash, is lighter than water, and burns with a bright flame. Silicium- 
ethyle is especially interesting as the source of a new alcohol in which a 
part of the carbon appears to be replaced by silicon. The formula of this 
alcohol is said to be SiC 8 H 20 0, which may be represented as the (missing, 
see p. 512) alcohol C 9 H 20 O, (nonyle-alcohol), in which an atom of carbon 
is replaced by an atom of silicon. 

Silicium-hexethyle, Si 2 E 6 , corresponding in composition to aluminum 
ethide, is also an inflammable liquid, the vapour of which has the high 
specific gravity 7*96. 

Silicium-methyle, Si(CH 3 ) 4 is obtained by the action of chloride of 
silicon upon iodide of methyle in the presence of zinc. It is a liquid 
which burns with a luminous flame, producing white fumes of silica. 

382. The following table exhibits the composition of the principal com- 
pounds of alcohol-radicals with inorganic elements which have yet been 
analysed, omitting some of the compound ammonias, which will be noticed 
hereafter : — 



Compounds of alcohol-radicals 




Inorganic 


with inorganic elements. 




Type. 


Sodium-ethyle, .... 


NaE 


NaCl 


Magne siuni - ethyle, 








MgE 2 


MgCl 2 


Aluminum-ethyle, 








A1 2 E 6 


A1 2 C1 6 


Zinc-methyle, . 








ZnMe 2 


ZnCl 2 


Zinc-ethyle, 








ZnE 2 


ZnCl 2 


Zinc-amyle, 








ZnAyl 2 


ZnCl 2 


Stan-methyle, 








SnMe 2 


SnCl 2 


Stan-ethyle, 








SnE 2 


SnCl 2 


Sesquiethide of tin, 








Sn 2 E 6 


Sn 2 3 


Diethiodide of tin, 








Sn 2 E 4 I 2 


Sn 2 3 


Stannic ethide, . 






SnE 4 


SnCl 4 



528 



CONSTITUTION OF ORGANO-METALLIC RADICALS. 



Compounds of alcohol-radicals 


Formula. 


Inorganic 


with inorganic elements. 




Type. 


Stannic ethylomethide, 


SnE 2 Me 2 * 


SnCl 4 


Stannic iodethide, 


SnE 2 I 2 


SnCl 4 


Bismnthous etliide, . 


BiE 3 


BiCl 3 


Bismuthous dichlorethide, . 


BiECl 2 


BiCLj 


Plumbic ethide, .... 


PbE 4 


Pb0 2 


Mercuric ethide, . . . 


HgE 2 


HgCl 2 


Mercuric methide, . . . • 


HgMe 2 


HgCl 2 


Stibethyle, .... 


SbE 3 


SbCl 3 


Antimonic triethoxide, 


SbE 3 


SbCl 5 


Iodide of tetrethyl-stibonium, . 


SbE 4 I 


SbCl 5 


Kakodyle, ..... 


AsMe 2 


As 2 S 2 


Oxide of kakodyle, 


As 2 Me 4 


As 2 3 


Arsenious oxymethide, 


AsMeO 


AsClg 


Trimethyle-arsine, 


AsMe 3 


AsCl 3 


Monomethyl arsenic acid, . 


AsMe0 2 


AsCl 5 


Kakodylic acid, .... 


HAsMe 2 2 


HAs0 3 ? 


Sulphokakodylic acid, 


(AsMe 2 ) 2 S 3 


As 2 5 


Terchloride of kakodyle, 


AsMe 2 Cl 3 


AsCl 5 


Arsenic triethoxide, . 


AsE 3 


AsCl 5 


Oxide of tetrethylarsonium, 


(AsE 4 ) 2 


As 2 5 


Oxide of dimethyl-diethylarsonium, 


(AsMe 2 E 2 ) 2 


As 2 5 


Triborethyle, .... 


BE 3 


BC1 3 


Boric methide, 


BMe 3 


BC1 3 


Silicium-ethyle, 


SiE 4 


SiCl 4 


Silicium-methyle, 


SiMe 4 


SiCl 4 



These compounds are evidently formed upon the types of the inorganic 
combinations of the respective elements. Those elements which combine 
in only one proportion with oxygen or sulphur, also combine in one pro- 
portion with an alcohol-radical ; whilst those which form more than one 
compound with oxygen and sulphur also generally form corresponding 
compounds with alcohol-radicals. 

Thus zinc, which combines with only two atoms of chlorine or bromine, 
also associates itself with two of methyle, ethyle, or amyle. Aluminum 
also combines only in one proportion with the alcohol-radicals, but that 
proportion corresponds with the composition of alumina, the only oxide 
of aluminum. 

Tin, on the other hand, forms three distinct series of compounds with 
the alcohol-radicals, composed according to the types of the protoxide, 
sesquioxide, and binoxide of tin, respectively. And it must be observed 
that as long as the type is adhered to, the particular radical occupying a 
place in the compound appears to be a matter of indifference ; thus we 
find, in the bodies composed after the type of sesquioxide of tin (Sn 2 3 ), 
one in which the places of the three atoms of oxygen are occupied by 
ethyle, and another in which only two of the places are occupied by 
ethyle (an electro-positive or quasi-metallic or bcwylous radical), whilst the 
third is filled by iodine (an electro-negative or cldorous radical). 

* Formed by the action of zinc-methvle upon the stannic iodethide, ZrjMe 2 + SnE 2 I 2 = 
SuE 2 Me 2 + Znl 2 . 



CONSTITUTION OF THE ALKALOIDS. 



529 



OKGANIC ALKALOIDS— AMMONIA. 

383. The attraction which the vegetable alkaloids have always possessed 
for the chemical inquirer is easily accounted for ; composing, as they do, so 
very small a portion of the plants in which they are found, and yet repre 
senting, in many cases, the whole virtue and activity of such plants in 
their action upon the animal body, it is very natural that their composi- 
tion should have been very carefully studied, with a view to explain the 
changes by which they are produced in the plants, and, if possible, to 
imitate those changes in order to obtain these valuable remedies by arti- 
ficial means. In this study, however, the chemist has to contend with 
difficulties of no insignificant character ; for even in the determination of 
the ultimate composition of these alkaloids, their high molecular weights 
and comparatively small proportion of hydrogen render the exact determin- 
ation of this element a matter of great difficulty, so that even at the 
present time the composition of some of the less known alkaloids can 
hardly be said to be definitely established. 

The following table includes the most important of those alkaloids 
which are extracted from plants : — 



Alkaloid. 


Source. 


Formula. 


Morphine 


Opium .... 


C l7 H 19 N0 3 


Codeine 


>j 






C 18 H 21 N0 3 


Narcotine 


>> 






C 22 H 23 N0 7 


Papaverine 


j ? 






C 20 H 21 NO 4 


Quinine 


Cinchona bark 






^20^24^2^2 


Cinchonine 


>> •■ 






C 20 H 24 N 2 O 


Quinidine 


>j 






^20^24^2^2 


Caffeine 
Theine 


Coffee . 
Tea 




1 


C 8 H 10 N 4 O 2 


Theobromine 


Cacao-nut 






C 7 H 8 N 4 2 


Strychnine 


Nux vomica . 






C 21 H 22 N 2 2 


Brucine 


»> 






C23H26N2O4 


Nicotine 


Tobacco . , 






C 10 H 14 N 2 


Solanine 


Potato-shoots . 








Atropine 


Deadly nightshade 




! 


C 17 H 9 oNOo 


Daturine 


Stramonium 




i 


y - / ±/ J -*~2o 


Cocaine 


Coca-deaves 






C 17 H 21 N0 4 


Hyoscyamine 


Henbane . 








Emetine 


Ipecacuanha 








Aconitine 


Aconite . 








Veratrine 


"White hellebore 






^32^52^208 


Coniine 


Hemlock . 






C 8 H 15 N 


Piperine 


Pepper 






C 17 H 19 N0 3 (?) 


Capsicine 


Cayenne pepper 








Sparteine 


Common broom 






C 15H 26 N " 2 


Curarine 


Curara poison . 






c ioHi 5 N 



From this table it is seen that the alkaloids invariably contain nitrogen ; 
and though this element generally forms a comparatively small part of 

2l 



530 ETHYL ATED AMMONIAS. 

the weight of the alkaloid, not exceeding 31 per cent, in theobromine, 
which is the richest in nitrogen, and falling as low as 3'4 per cent, in 
narcotine, which is the poorest, it is from this element that chemists have 
always started in their speculations upon the constitution of these impor- 
tant bodies. 

The earliest view of any importance respecting the constitution of the 
alkaloids was that of Berzelius, who, resting upon the constant presence 
of nitrogen and hydrogen in these substances, regarded them as compounds 
of certain neutral substances (then unknown in the separate state) with 
ammonia, to which they owed their alkaline characters, and this opinion 
was much strengthened when it was discovered that certain organic bases 
(though not those actually found in plants) could be produced by the 
direct combination of ammonia with neutral substances ; thus oil of 
mustard (C 4 H 5 NS), when combined with ammonia (NH,), yields the base 
thiosinnamine (C 4 H 8 N" 2 S). 

To this view it was objected, that ammonia could not be detected in 
these organic bases, and as the doctrine of the displacement of one element 
by another, or by a quasi-element, gained ground, it was suggested that 
the organic bases might be really constituted in the same manner as 
ammonia itself, the place of a portion of the hydrogen being occupied by 
a group composed of carbon and hydrogen, or of carbon, hydrogen, and 
oxygen. This view of the constitution of the alkaloids, therefore, would 
at once propose ammonia as the type of this large class. 

In the earlier attempts to refer the organic bases to ammonia as their 
type, it was said that just as that substance is composed of four atoms 
(one of nitrogen and three of hydrogen), so are the organic bases, but that 
these contain only two separate hydrogen-atoms, the place of the third 
atom of that element being occupied by a compound which discharges the 
functions of that third atom of hydrogen, and does not destroy the alka- 
line character of the original ammonia type. 

To apply this view to one of the least complex of the organic bases, 
aniline (C 6 H 7 N), we might represent it as ammonia (NH 3 ), in which the 
third atom of hydrogen had been displaced by the hypothetical compound 
radical phenyle (C 6 H 5 ) for C 6 H 7 N = NH 2 .C 6 H 5 , phenylamine. 

This view of the constitution of aniline was supported by the fact, that 
aniline may be obtained by the action of heat upon phenate of ammonia ; 
thus — 

jm,C,H,0 - H.0 = WH 2 .C 6 H 5 

Phenate of Ammonia. Aniline. 

and as the substances derived from ammoniacal salts by the loss of a 
molecule of water were called amides (being supposed to contain amido- 
gen, NH 2 , this theory was spoken of as the amide-theory of the consti- 
tution of organic bases. 

Later research has only extended this theory, having proved that 
ammonia is the type of at least the greater number of organic bases, and 
that not only one, but all three of the hydrogen-atoms, are moveable, and ' 
may be displaced by compound radicals, whilst even the nitrogen of the 
type also admits of replacement by other elements of the same chemical 
family, viz., by phosphorus, arsenic, and antimony. 

A more instructive example of the elasticity of a type cannot be given. 

384. Ethylated ammonias and their derivatives. — When iodide of 
ethyle (C. 2 H 5 I) is heated in a sealed tube with an alcoholic solution of 



ETHYL AMINE. 531 

ammonia, in the proportion of single molecules, a crystalline compound 
is formed, which, might at first be regarded merely as a combination of 
the two bodies employed to produce it (C 2 H-I.NH 3 ); but when this 
substance is distilled with potash, it furnishes, instead of ammoniacal gas, 
a vapour which condenses, under the ordinary pressure in a receiver cooled 
by ice, to a very light colourless liquid which boils at 65 0, 6 F., and has 
a powerful ammoniacal odour. By analysis, this liquid is found to have 
the composition C 2 H 7 N, being, in fact, ammonia in which one-third of the 
hydrogen has been displaced by ethyle. That this is the true view of its 
constitution does not admit of a doubt, since it so nearly resembles 
ammonia in all its characters, that it might easily be mistaken for that 
substance. The ethyl-ammonia oxethylia, or ethylamine, has not only the 
modified odour of ammonia, but is powerfully alkaline, and combines 
readily with acids, forming salts, many of which may be crystallised. It 
is, as might be expected, more inflammable than ammonia. 

The crystalline compound formed by the action of iodide of ethyle upon 
ammonia is the hydriodate of ethylamine — 



' 2 — 5 -. 



H 




rc H 


H = 


= N< 


H 


H 




H 



C.HJ + 1S< H = N^ H V.HI 



the hydrogen expelled from the ammonia having taken the place of the 
ethyle in the iodide, forming hydriodic acid, which remains in combina- 
tion with the ethylamine. 

Chloride of ethyle and bromide of ethyle, when heated with ammonia, 
yield, respectively, the hydrochlorate and hydrobromate of ethylamine, but 
the iodide of ethyle is preferred for this and similar experiments, as being 
less volatile, and therefore, more manageable in sealed tubes. 

When the hydriodate of ethylamine is distilled with potash, it behaves 
just as hydriodate of ammonia would do if similarly treated — 



NH 3 .HI + KHO 


= NH 3 + KI + H 2 


Hydriodate of ammonia. 


Ammonia. 


NH 2 .C 2 H 5 .HI + KHO 


= NH 2 .C 2 H 5 + KI + 



H 2 0. 

Hydriodate of ethylamine. Ethylamine. " 

Ethylamine also combines with the oxygen acids in the same manner 
as ammonia — 

Sulphate of ammonia, . . . 2NH 3 .H 2 O.S0 3 
Sulphate of ethylamine, . . 2(KH 2 .C 2 H 5 ).H 2 O.S0 3 . 

If any further proof were wanted that ethylamine is really composed after the 
type of ammonia, it would be afforded by the circumstance, that ethylamine may be 
prepared by distilling cyanic ether with caustic potash. 

Cyanic ether (C 2 H 5 CyO = CgHgCNO) is obtained by distilling sulphovinate of 
potash with cyanate of potash — 

KCyO + KC 2 H 5 S0 4 = C 2 H 5 CyO +K 2 S0 4 . 
Cyanate of potash. Sulphovinate of potash. Cyanic ether. 

Now, cyanic ether is simply cyanic acid, in which an atom of ethyle occupies the 
place of an atom of hydrogen — 

Cyanic acid, . . . HCyO 

Cyanic ether, . . . ECyO . 

"When cyanic acid is distilled with caustic potash, it yields ammonia and carbonate 
of potash — 

HCNO + 2KHO = NH, + K 9 O.C0 2 



532 TETRETHYLIUM. 

and since cyanic ether contains an atom of ethyle, in place of an atom of hydrogen, 
it would be expected to furnish an ammonia in which a similar displacement had 
been effected — 

ECNO + 2KHO = NH 2 E + K 2 O.C0 2 . 

Cyanic ether Ethylamine. 

If ethylamine be again acted upon by iodide of ethyle, a second atom 
of hydrogen may be displaced by ethyle, and the hydriodate of diethyla- 
mine is obtained — 

N 





C 2 H 5 


+ C 2 H 5 I = N-^C 2 H 5 V.HI 


( H j 


Ethylamine. 


Iodide of Hydriodate of diethylamine. 



ethyle. 

and from this hydriodate the diethylamine is obtained by distillation with 
potash, as a colourless and inflammable liquid, strongly ammoniacal, and 
having a much, higher boiling point than ethylamine (134 0, 6F.) In its 
chemical relations diethylamine is a decided ammonia. 

In order to remove the third atom of hydrogen, it is only necessary to 
subject diethylamine to the action of iodide of ethyle — 

NJOftV + C. 2 H 5 I = N^C s hA.HI 

Diethylamine. Iodide of Hydriodate of triethylamine. 

ethyle. 

When this last hydriodate is distilled with potash, the triethylamine is 
obtained as a colourless liquid, presenting the strongest evidence of its 
relationship to ethylamine and diethylamine as well as to ammonia. It is 
powerfully alkaline, and boils at a higher temperature than diethylamine.* 

But the action of iodide of ethyle does not stop here, for if triethyla- 
mine be again heated with it, a molecule of that base combines with a mole- 
cule of the iodide to form the compound N(C 2 H 5 ) 3 .C 2 H 5 I, which may be 
represented as hydriodate of triethylamine in which the place of the 
hydrogen in the hydriodic acid is occupied by ethyle. 

But it will be remembered that the hydriodate of ammonia (NH 3 .HI) 
is sometimes regarded as the iodide of a hypothetical compound metal 
ammonium (NH 4 ), and it would appear admissible to view the above 
compound as iodide of ammonium (NH 4 I), in which the four atoms of 
hydrogen are displaced by ethyle ; it would then be called iodide of tetre- 
thylammonium (NE 4 I), or iodide of tetrethylium. 

Unlike the preceding compounds, the iodide of tetrethylium may be 
boiled with solution of potash without decomposition, but if a solution of 
this substance be treated with oxide of silver, iodide of silver is formed, 
and when the solution is filtered and evaporated in vacuo over sulphuric 
acid, it deposits needle-like crystals having the composition N(C 2 H 5 ) 4 HO. 
This substance, which is called the hydrate of tetrethylium, is exactly 
similar in properties to the hydrates of potash and soda ; it is deliques- 
cent, absorbs carbonic acid eagerly from the air, is exceedingly alkaline 
and caustic, expels ammonia from its salts, forms soap with the fats, and 
behaves in every respect like the hydrate of a fixed alkali. Its taste is 
very bitter as well as alkaline. 

* Just as ethylamine is obtained by the action of hydrate of potash upon cyanic ether, so 
triethylamine is formed when ethylate of potash (potassium-alcohol) acts upon cyanic ether— 

ECNO H 2(KEO) = NE 3 + K,O.C0 2 . 



AMMONIUM BASES. 533 

It is obviously not an ammonia, but is composed after the type of 
caustic potash (KHO), and contains, in place of the potassium, the 
hypothetical radical tetrethylium, N(C 4 H 5 ) 4 , or ammonium (NH 4 ) in which 
the four atoms of hydrogen have been displaced by ethyle. 

The action of oxide of silver upon the iodide of tetrethylium is now 
intelligible — 

2NE 4 I + Ag 2 + H 2 = 2KE 4 HO + 2AgI. 

Iodide of Hydrate of 

tetrethylium. tetrethylium. 

The new alkali is easily decomposed ; even at a temperature below the 
boiling point of water, it is resolved into triethylamine, olefiant gas, and 
water — 

N(C 2 H 5 ) 4 HO = N(C 2 H 5 ) 3 + C. 2 H 4 + H 2 0. 

Triethylamine. 

It will be remembered that the solution of ammonia in water may be 
regarded as containing the hydrate of ammonium, for — 

NH 3 + H 2 = NH 4 HO 

which latter would be the true type of the hydrate of tetrethylium ; 
but so great is the want of stability in this case, that all attempts to 
isolate the hydrate of ammonium have resulted in the production of 
ammonia and water. 

Like potash, the oxide of tetrethylium is capable of forming salts with 
the oxygen-acids without the intervention of a molecule of water, thus — 

Sulphate of potash, . . . K. 2 O.S0 3 
Sulphate of oxide of tetrethylium, . (NE 4 ) 2 O.S0 3 . 

It would naturally be expected that by the action of the iodides of 
other alcohol radicals upon ammonia, compounds should be obtained 
corresponding to those belonging to the ethyle series ; thus we have — 

( Type ; ammonia NH 3 ). 

Diamylamine, NH.(C 5 H n ) 2 



Trimethylamine, N(CH 3 ) 3 
Triethylamine, N(C 2 H 5 ) 3 
Triamylamine,t N(C 5 H n ) 3 



Methylamine, * NH 2 . CH 3 

Ethylamine, NH 2 .C 2 H 5 

Amylamine, NH 2 . C 5 H n 

Dimethylamine, NH. (CH 3 ) 2 

Diethylamine, NH. (C 2 H 5 ) 2 

(Type; imaginary hydrate of ammonium, NH 4 HO.) 

Hydrate of — 

Tetramethylium, N(CH 3 ) 4 HO 
Tetrethylium, N(C 2 H 5 ) 4 HO 
Tetramylium, N(C 5 H n ) 4 HO 

But even here, the elasticity of the types and the replacing power of 
the alcohol-radicals are not exhausted. 

If methylamine (NH 2 .Me) be acted upon by iodide of ethyle, the 
hydriodate of methyl-ethylamine is formed — 

NH 2 .Me + EI = NHMeE.HI 

, r ... n . Iodide of Hydriodate of methyl- 

Methylamme. ethyle> ethylamine. 

* Methylamine, which is a gas at the ordinary temperature, is far more soluble in water 
than any other gas ; water dissolves 1150 volumes of methylamine, the solution exactly 
resembling that of ammonia. 

t Even the hypothetical hydrocarbon cetyle (C 18 H ?3 ), the radical of ethal, has been sub- 
stituted for the nitrogen in ammonia. The base tricetylamine, N(C 16 H 33 ) 3 , which is thus 
formed, contains only 2 per cent, of nitrogen. 



534 PHENYLAMINE. 

and by distilling this with potash, the methyl-ethylaniine, much resem- 
bling the other ammonia bases, is obtained. 

Again, on subjecting this base to the action of iodide of amyle, and 
distilling the product with potash, a new ammonia base is procured, in 
which all three atoms of hydrogen are replaced by different radicals ; 
this base is called methyl-ethyl-amylamine, and its composition is repre- 
sented by the formula N(CH 3 ) (C 2 H 5 ) (C 5 H n ) = NMeEAyl. 

If we had started with aniline (phenylamine, NH 2 .C 6 H 5 ) in the above 
experiment, treatment with iodide of methyle would have furnished 
methyl-aniline or methyl-phenylamine, NH.C 6 H 5 .CH 3 ; and by treating 
this with iodide of ethyle, we should obtain ethyl-methyl-phenylamine, 
NC 6 H 5 .CH 3 .C 2 H 3 ; the action of iodide of amyle upon this last ammonia 
would give the iodide of methyl ethyl- amylo-phenylium, and on decompos- 
ing this with oxide of silver there would be obtained the hydrate of 
methylethyl-amylo-phenyl-ammonium — 

N(CH 3 ) (C 2 H 5 ) (CHJ (C 6 H 5 )HO 

a base formed upon the hypothetical type of hydrate of ammonium, in 
which each of the four atoms of hydrogen is replaced by a different 
radical. 

This complex substance affords an excellent example of the difference 
between an empirical and a rational formula ; its empirical formula, 
C 14 H 25 NO, which simply shows the result of its ultimate analysis, teaches 
nothing with respect to its constitution, which is at once clear when the 
rational formula as above written is placed before us. 

Phenylamine, NH 2 (C 6 H 5 ), is found among the products of the destructive dis- 
tillation of rosaniline (p. 452), whilst ethyl-rosanilme (aniline-violet) yields ethyl- 
phenylamine or ethyl-aniline, NH(C 6 H 5 ) (C 2 H 5 ), and phenyl-rosaniline {aniline blue) 
yields di-phenylamine or phenyl-aniline, NH(C 6 H 5 ) 2 . 

Diphenylamine lias also been obtained by digesting hydrochlorate of aniline with 
free aniline at a high temperature, when hydrochlorate of diphenylamine is obtained, 
which is decomposed by a large excess of warm water, the diphenylamine rising to 
the surface as an oil which solidifies on cooling. The change may be expressed by 
the following equation : — 

NH 2 (C 6 H 5 ).HC1 + NH 2 (C 6 H 5 ) = NH(C 6 H 5 ) 2 .HC1 + NH 3 . 
Hydrochlorate of aniline,. Aniline. *%$$£&« 

Ditoluylamine, NH(C 7 H 7 ) 2 , may be procured in a similar way by digesting hydro- 
chlorate of toluidine with toluidine. 

Phenyl-toluylamine, NH(C 6 H 5 ) (C 7 H 7 ), is formed by the action of aniline on hydro- 
chlorate of toluidine, or by that of toluidine on hydrochlorate of aniline. 

Under the action of nitric acid, di-phenylamine gives rise to di-nitro-diphenyla- 
mine, NH[C 6 H 4 (N0 2 )] 2 , in which the same type is preserved, though nitric peroxide 
(N0 2 ) is substituted for one-fifth of the hydrogen in the phenyle. 

When treated with chloride of benzoyle (C 7 H 5 0.C1), diphenylamine yields diphenyl- 
benzoylamine, 1ST(C 6 H 5 ) 2 (C 7 H 5 0). 

It will be observed that certain of these bases derived from the alcohols 
have the same empirical formulae as those derived from coal-tar and other 
sources, with which, however, they are by no means identical. Thus, tolui- 
dine (C 7 H 9 N) has the same composition as methyl-aniline (NH.C 6 H 5 .CHJ ; 
but the former is a crystalline solid, and the latter an oily liquid. Again, 
when iodide of ethyle acts upon toluidine, an atom of hydrogen is 
displaced by ethyle, and ethylo-toluidine is obtained. The composition 
of this base, C 7 H 8 (C 2 H 5 )N, is the same as that of methyl-ethyl-aniline, 
N(CH 3 ) (C 2 H.) (C 6 H 5 ), and as that of cumidine (C 9 H 13 N) ; but in their 



POLY-AMMONIAS. 535 

chemical properties these bodies exhibit such a difference as would be 
expected from the difference in their constitution. 

385. Investigation of the constitution of the alkaloids. — It will be evi- 
dent that the principles developed in the experiments just described may- 
be applied in investigating the constitution of the bases extracted from 
plants. Let it be supposed that ethylamine (C 2 H 7 N) was a vegetable 
alkali of unknown constitution ; when it was found that by the action of 
iodide of ethyle two out of the seven atoms of hydrogen could be dis- 
placed, it would be at once inferred that these two atoms occupied a very 
different position from the other five, and that the constitution of the 
compound would be more properly expressed by writing the formula 
C 2 H 5 .H 2 N. On applying the same principle to the examination of the 
natural alkaloid coniine (C 8 H 15 !N), it was found possible, by the action of 
iodide of methyle, to remove only one atom of the hydrogen, so that the 
formula C 8 H 14 .HN would more correctly represent the constitution of 
coniine, which might be then regarded as ammonia in which two atoms 
of the hydrogen have been displaced by the group C 8 H 14 , or in which 
each of these atoms has been displaced by the group C 4 H 7 . 

If we were acquainted with an iodide of this group, we have every 
reason to expect that its action upon ammonia would lead us to the arti- 
ficial formation of coniine.* 

Mcotine, morphine, and codeine will not part with any of their hydro- 
gen under the action of iodide of ethyle, and must therefore be placed 
upon the same footing as triethylamine, N(C 2 H 5 ) 3 , in which all three 
atoms of hydrogen are already replaced. Upon this view they would be 
represented thus — 

Mcotine, N(C 5 H.) W 

Morphine, N(C 17 H 19 3 ) /// 

Codeine, N(C 18 H 21 3 )"' . 

The mark ('") signifying that the groups are triatomic, or have the same 
replacing value as three atoms of hydrogen. When these bases are acted 
upon by the iodides of alcohol-radicals, there are formed, as would be 
expected, iodides upon the type NH 4 I, from which may be obtained fixed 
alkalies resembling the hydrate of tetrethylium. Thus we have the 
hydrates 

Methyhmorphyl-ammonium, N(C 17 H 19 3 ) /// (CH 3 )HO 
Ethyl-codyl-ammonium, JS"(C 18 H 21 3 ) ,/ (C 2 H 5 )HO 

Ethyl-nicotyl-ammonium, N(C 5 H 7 ) w (C 2 H 5 )HO ,// . 

386. Poly-ammonias. — In speculating upon the constitution of the 
vegetable bases, it must not be forgotten that some of them contain 
two atoms of nitrogen ; this is the case, for example, with cinchonine 
(C 20 H 24 ISr 2 O), quinine (C 20 H 2i ^ 2 O 2 ), and strychnine (C 21 H 22 N 2 2 ). If the 
whole of the nitrogen in these bases be due to the ammonia type, they 
must be composed after the type of a double atom of ammonia, N 2 H 6 . In 
the case of strychnine, it is found that the action of iodide of ethyle fails 
to remove any portion of the hydrogen, so that if the base be really com- 
posed after the ammonia type, it must be represented by two atoms of 
ammonia (N~ 2 H 6 ), in which the whole of the hydrogen has been displaced 

* The group C 4 H 7 is often assumed as the radical of butyric acid (C 4 H 8 2 ), and it ia at 
least a curious coincidence, that when acted upon by nitric acid, coniine actually yields 
butyric acid. 



536 DIAMINES. 

by the group (C 21 H 22 2 ), when its formula would be N 2 (C 21 PI 22 2 ) vi , the 
replacing group in this case being hexatomic, or equivalent to six atoms 
of hydrogen. That it is by no means necessary for each atom of hydrogen 
to be displaced by a single group or radical, is seen in a great many organic 
compounds ; thus, in chloroform (CH)C1 3 , we have the triatomic group 
CH (commonly called formyle) occupying the position of three atoms of 
hydrogen which would be required to combine with the three atoms of 
chlorine ; again, in Dutch liquid, (C 2 H 4 )C1 2 , we have the diatomic group 
C 2 H 4 (ethylene) occupying the place of two atoms of hydrogen. 

If the view above explained with respect to the constitution of some of 
the natural alkaloids be correct, it ought to be possible to form artificially 
a base in which two or three atoms of hydrogen have been displaced by 
means of a diatomic or triatomic radical. 

387. Diamines, — When olefiant gas or ethylene, C 2 H 4 , is brought in 
contact with bromine, the compound C 2 H 4 Br 2 , corresponding to Dutch 
liquid (C 2 ELC1 2 ), is obtained, and from the action of ammonia upon this 
bibromide of ethylene, there is derived a new alkaline base, having the 
composition N 2 H 4 (C 2 H 4 ) // , or two molecules of ammonia (N 2 H 6 ), in which 
the diatomic ethylene replaces two atoms of hydrogen. Such bases, formed 
upon the double ammonia type, are called diamines, whilst those which 
correspond to a single molecule of ammonia are called monamines. The 
base above mentioned is named ethylene-diamine. The diamines, like the 
double atom of ammonia from which they are derived, are capable of 
combining with two molecules of hydrochloric or any similar acid, which 
is implied by stating that they are diacid. 

"When Dutch, liquid (bichloride of ethylene, (C 2 H 4 )"C1 2 ), is heated to 300° F. with strong 
ammonia in a sealed tube, an action takes place corresponding to that of a double 
molecule of hydrochloric acid (H 2 C1 2 ) upon a double molecule of ammonia (N 2 H 6 ), 
which would give rise to a double molecule of hydrochlorate of ammonia (N 2 H 6 .H 2 C1 2 ) ; 
in the product of the action of Dutch liquid upon ammonia (N 2 H 4 (C 2 H 4 ) 2 "C1 2 ), the 
places of four atoms of hydrogen are occupied by two molecules of the diatomic group 
(C 2 H 4 ). But here the correspondence ceases, for whilst the hydrochlorate of ammonia, 
when decomposed with oxide of silver, would yield ammonia and chloride of silver, 
the new compound, when thus treated, yields a fixed alkaline base, resembling caustic 
potash, and having the composition N 2 H 4 (C 2 H 4 ) 2 ".H 2 2 , which represents a double 
molecule of the hypothetical hydrate of ammonium 2(NH 4 HO), in which four atoms of 
hydrogen have been displaced by two molecules of the diatomic ethylene. The name 
hydrate of diethylene-diammonium expresses the composition of this substance, 
which is remarkable for its stability, a temperature above 300° F. being required to 
effect its decomposition, when it furnishes a volatile alkali, having the composition 
N 2 H 2 (C 2 H 4 ) 2 ", and called diethylene-diamine, being evidently formed from a double 
molecule of ammonia, in which four atoms of hydrogen are replaced by two of the 
diatomic ethylene. Its production may be explained by the equation — 

N 2 H 4 (C 2 H 4 ) 2 "H 2 2 = N 2 H 2 (C 2 H 4 ) 2 " + 2H 2 . 

By acting upon the new ammonia with iodide of ethyle (C 2 H 5 I), the two atoms 
of hydrogen may be displaced by ethyle, yielding diethyl -diethylene-diamine, 
N 2 (C 2 H 5 ) 2 (C 2 H 4 ) 2 ", or a double molecule of ammonia (N 2 H 6 ), in which H 2 are replaced 
by two of ethyle, and H 4 by two of ethylene. 

By treating phenylamine (aniline), NH 2 (C 6 H 5 ), with bichloride of ethylene (Dutch 
liquid), the diphenyl-diethylene-diamine, N 2 (C 6 H 5 ) 2 (C 2 H 4 ) 2 ", is obtained, which repre- 
sents a double molecule of ammonia (N 2 H 6 ), in which H 2 are replaced by two of 
phenyle, and H 4 by two of ethylene. By the action of chloroform upon aniline, 
formyl-diphenyl- diamine, N 2 (('H)'"(C 6 H 5 ) 2 H, has been obtained, in which H 3 are 
replaced by the triatomic formyle (CH), and H 2 by phenyle. 

It has been seen that phenylamine is produced by the deoxidising action of ferrous 
acetate upon nitrobenzole (C 6 H 5 .ND 2 ). When di-nitrobenzole is treated in a similar 
way, phenylene-diamine, N 2 H 4 (C G H 4 )", is obtained, which is evidently derived from a 



TRIAMINES OR TRIPLE AMMONIAS. 537 

double molecule of ammonia, in which H ? are replaced by the diatomic group pheny- 
lene (C 6 H 4 ), which bears the same relation to phenyle (C 6 H 5 ) as ethylene (C 2 H 4 ) 
bears to ethyle (C 2 H 5 ). By treating di-nitrotoluole and di-nitrocumole with ferrous 
acetate, tolylene-diamine and cumylene-diamine are obtained, which are diammonias, 
in which H 2 are replaced by the diatomic radicals tolylene (C 7 H 6 )" and cumylene 
(C 9 H 10 )". These three diamines are called the aromatic diamines, since the diatomic 
groups phenylene, tolylene, and cumylene are closely connected, through benzole 
(C 6 H 6 ), toluole (C 7 H 8 ), and cumole (C 9 H 12 ), with the aromatic acids, benzoic 
(C 7 H 6 2 ), toluic (C 8 H 8 2 ), and cuminic (C 10 H 12 O 2 ). 

Paraniline (C 12 H 14 N\>) is obtained as a secondary product in the manufacture of 
aniline, with which it is polymeric. Its properties are very different from those of 
aniline, for it is solid at the ordinary temperature, forming silky needles which melt 
when heated, and boil beyond the range of the thermometer, distilling unchanged. 
It combines with acids, forming beautiful crystalline salts, the study of which proves 
it to be a diamine. 

388. Triamines. — The triarm'nes are formed upon the type of a treble 
molecule of ammonia (N 3 H 9 ), in which, the hydrogen is replaced either 
entirely or in part by other radicals. Thus, diethylene-triamine, 
Jsr 3 H 5 (C 2 H 4 ) 2 // , and triethylene-triamine, N 3 H 3 (C 2 H 4 ) 3 ", are obtained by 
the action of bi-bromide of ethylene (C 2 H 4 Br 2 ) upon ammonia. They 
are powerfully alkaline liquids, which are capable of absorbing carbonic 
acid from the air. The triamines are generally capable of forming three 
classes of salts, the monacid, diacid, and triacid salts, containing respect- 
ively one, two, and three equivalents of acid. 

Di-ethylene-di-ethyl-triamine, N 3 H 3 (C 2 H 4 ) 2 "(C 2 H 5 ) 2 , is produced by the joint action 
of ethylamine and ammonia upon bibromide of ethylene — 

2[(C 2 H 4 )"Br 2 ] + 3NH 2 (0 2 H 5 ) + NH 3 = 
N 3 H 3 (C 2 H 4 ) 2 "(C 2 H 5 ) 2 .3HBr + NH 2 (C 2 H 5 ).HBr. 

It forms splendidly crystallised salts, and is evidently derived from three molecules 
of ammonia (N 3 H 9 ), by the substitution of two molecules of ethylene (C 2 H 4 ) 2 " for H 4 , 
and of ethyle (C 2 H 5 ) 2 for H 2 . 

Carbotriamine (guanidine), N" 3 H 5 C iv , is a treble molecule of ammonia, in which 
four atoms of hydrogen are replaced by one atom of tetratomic carbon. It is formed 
by heating ammonia with subcarbonate (orthocarbonate) of ethyle in a sealed tube to 
about 300° F. 

2(C 2 H 5 ) 2 O.C0 2 + 3NH 3 + H 2 = N 3 H 5 C.H 2 + 4(C 2 H 5 HO). 

The change is more clearly explained by representing the subcarbonate of ethyle as 
formed upon the type of four molecules of water (H 8 4 ) in which H 4 are replaced by 
(C 2 H 5 ) 4 , and the remaining H 4 by C iv . 

( ° 2H ^y j 4 + 3NH 3 + H 2 = N 3 H 5 C iv .H 2 + ( C ^U j ^ 
Subcarbonate of ethyle. Guanidine. 4 mols. alcohol. 

Guanidine may also be obtained by heating chloropicrine in a sealed tube, with 
an alcoholic solution of ammonia, to 212° F., when the following reaction ensues — 

2CC1 3 (N0 2 ) + 6KE 3 = 2(N 3 H 5 C.HC1) + 4HC1 + N 2 3 + H 2 0. 

Chloropicrine. Hydrochlorate of 

guanidine. 

It will be remembered that the subcarbonate of ethyle itself is obtained by the 
action of sodium upon an alcoholic solution of chloropicrine (p. 516). 

Melaniline, C 13 iI\ 3 N" 3 , a crystalline base, produced by the action of chloride of 
cyanogen upon aniline, may be regarded as diphenyl-guanidine, N 3 H 3 (C 6 H 5 ) 2 C, or 
guanidine in which two of phenyle have replaced two of hydrogen. 

The beautiful aniline dyes appear to be salts of certain triamines formed by the 
replacement of the hydrogen in a treble molecule of ammonia by hydrocarbon 
radicals. 

According to Hofmann, rosaniline, the base of the aniline red produced by the 
action of oxidising agents upon aniline containing toluidine, is possibly phenylene- 
ditolylene-triamine, N 3 (C 6 H 4 )"(C 7 H 6 ) 2 "H 3 . H 2 0, the phenylene being derived from the 



538 TETRAMINES. 

aniline, ]STH 2 (C 6 H 5 ), and the tolylene from the toluidine, NH 2 (C 7 H 7 ). Aniline blue, 
formed by the action of aniline upon aniline red, would be phenylene-ditolylene- 
triphenyl-triamine, N 3 (C 6 H 4 y'(C 7 H 6 ) 2 "(C 6 H 5 ) 3 .H 2 0, having been formed from rosani- 
line by the substitution of three of phenyle for H 3 . Aniline violet, the result of 
the action of iodide of ethyle upon rosaniline, would be phenylene-ditolylene triethyl- 
triamine, N 3 (C 6 H 4 )"(C 7 H 6 ) 2 "(C 2 H 5 ) 3 .H 2 0, or rosaniline containing three of ethyle 
in place of H 3 . 

The trichloride of diethylene-triammonium, ]ST 3 (C 2 H 4 ) 2 "H 8 . Cl 3 , has also been ob- 
tained. 

389. Tetramines are formed upon the type of four molecules of am- 
monia, and therefore contain four atoms of nitrogen, and are able to 
combine with, four atoms of a hydrogen acid. Thus, if bibromide of 
ethylene be allowed to act upon ethylene-diamine in the presence of 
hydrobromic acid, the hydrobromate of triethylene-tetramine is obtained — 

(C^y'Br, + 2N 2 (C 2 H 4 )"H 4 + 2HBr = F 4 (C 2 H 4 )/'H,4HBr. 

B "e.° £ E t W ene-dia m ,„e. ^S&SSSZL. 

and if this be decomposed with oxide of silver, a strongly alkaline solu- 
tion is obtained, which contains triethylene-tetramine, N 4 (C 2 H 4 )/H 6 , or 
a quadruple molecule of ammonia (JN" 4 H 12 ), in which half the hydrogen is 
replaced by three of diatomic ethylene. 

By acting on C 2 H 4 Br 2 with ethylamine, a salt is obtained, having the composition 
N 4 (C 2 H 4 V'(C 2 H 5 ) 4 H 2 .Br 4 , representing four molecules of bromide of ammonium 
(N 4 H 16 Br 4 ), in which H 10 are replaced by 5(C 2 H 4 )", and H 4 by (C 2 H 5 ) 4 . From this 
bromide a strongly alkaline base, the hydrate of pentethylene-tetrethyl-tetr-ammonium 
[N 4 (C 2 H 4 ) 5 "(C 2 H 5 ) 4 H 2 ]H 4 4 is obtained, which is formed upon the type of four mole- 
cules of the imaginary hydrate of ammonium (NH 4 HO). 

The action of iodide of ethyle (C 2 H 5 I) upon this base replaces each of the re- 
maining atoms of hydrogen by ethyle, yielding [N 4 (0 2 H 4 ) g "(C 2 H 5 ) 5 H]H 4 4 and 
[N 4 (C 2 H 4 )/(C. 2 H 5 ) 6 ]H 4 4 . 

When diethylamine (NH(C 2 H 5 ) 2 ) acts on bibromide of ethylene, the bromide of 
tri-ethylene-octethyl-tetrammonium, N 4 (C 2 H 4 ) 3 "(C 2 H 5 ) 8 H 2 . Br 4 , is obtained, which also 
furnishes a powerfully alkaline base [N 4 (C 2 H 4 ) 3 "(C 2 H 5 ) 8 H 2 ]H 4 4 . 

390. We are not entirely dependent upon purely artificial processes 
for the ammonia bases containing alcohol-radicals. Many processes of 
putrefaction furnish certain of these bases which had hitherto been over- 
looked in consequence of their resemblance to ammonia. Thus, putre- 
fying flour yields ethylamine, trimethylamine, and amylamine ; trimethyl- 
amine is also found in the roe of herrings, as also in putrefied urine and 
in the chenopodium vidvaria ; it may also be obtained by distilling ergot 
of rye with potash. Methylamine, ethylamine, prolamine (NH 2 .C 3 H 7 ), 
Udylamine (NH 2 .C 4 H 9 ), or petinine, and amylamine, are found among- 
the products of the destructive distillation of bones. 

391. Ammonias and ammonium bases containing phosphorus, arsenic, 
and antimony. — It might be expected that the ammonia type was not 
susceptible of any further modifications, but it has been found that even 
the nitrogen of that type may be represented by other elements which are 
chemically related to it. 

Antimony, arsenic, and phosphorus, it will be remembered, all form 
compounds with three atoms of hydrogen, SbH 3 , AsH 3 , and PH 3 , which 
may be regarded as formed upon the ammonia type. Neither of these 
substances, however, possesses any alkaline character, the last alone being 
capable of combining with, certain acids (hydrobromic and hydriodic). 

Mention has already been made of the circumstance that compounds 
corresponding to antimonietted, arsenietted, and phosphuretted hydrogen 



TRIETHYLPHOSPHINE. 539 

may be obtained, in which the place of the hydrogen is occupied by cer- 
tain alcohol-radicals ; but in these cases the hydrogen does not admit of 
partial replacement, only those compounds which correspond to triethyl- 
amine and trimethylamine having been obtained. 

Trietliylstibine, Sb(C 2 H 5 ) 3 , and triethylarsine, As(C 2 H 5 ) 3 , have already 
been noticed amongst another class of bodies to which they seem properly 
to belong, since they are not capable of forming salts corresponding to 
those of ammonia (see p. 528). 

With triethylphosphine, however, the case is different ; this substance, 
P(C 2 H 5 ) 3 , is a true ammonia, capable of forming salts with the acids, like 
ethylamine, although exhibiting, unlike that body, a very powerful ten- 
dency to combine directly with an atom of oxygen or sulphur, to form 
compounds resembling those of the arsenic and antimony series (see 
p. 528), and formed upon the type of phosphoric chloride (PC1 5 ). Thus 
we have — 

Oxide of triethylphosphine, PE 3 

Sulphide, .... PE 3 S 

and the corresponding compounds containing methyle. 

Triethylphosphine is obtained by the action of terchloride of phos- 
phorus upon zinc-ethyle, 2PC1 3 + 3ZnE 2 = 2PE 3 + 3ZnCl 2 . It is a 
volatile liquid of a very peculiar powerful odour, the vapour of which, 
when mixed with oxygen, explodes with great violence at a temperature 
far below 212°. 

By acting upon triethylstibine, or stibio-triethyle, with iodide of ethyle, 
an iodide is obtained which, when decomposed by oxide of silver, yields 
the hydrate of tetrethylstibonium (SbE 4 HO), formed after the type of 
hydrate of ammonium (£TH 4 HO). 

In a similar manner there are obtained the hydrates of tetrethyl- 
arsonium (AsE 4 HO) and tetrethylphosphonium (PE 4 HO), and their 
corresponding methyle compounds. 

These substances are precisely similar in properties to the hydrate 
of tetrethylium, being powerfully caustic alkalies bearing a close resem- 
blance to caustic potash. 

A very remarkable base has also been obtained, composed after the type 
of a double molecule of the imaginary hydrate of ammonium (N 2 H 8 H 2 2 ), 
in which one atom of nitrogen has been replaced by phosphorus, and the 
other by arsenic, whilst, of the hydrogen, two atoms are replaced by the 
diatomic radical ethylene (C 2 H 4 ) // , aad the remainder by ethyle. This 
base has been styled the hydrate of ethylene-hexethyle-diphospharsonium, 
and its formula is — 

PAs(C 2 H 4 )^(C 2 H 5 ) ti H 2 0, 

This base combines with two molecules of acids to form salts, and behaves 
in every respect as a double molecule of caustic potash would do. 

By acting upon triethylphosphine with chloroform (CHC1 3 ), contain- 
ing the triatomic radical formyle (CH)'", a chloride has been obtained 
which is composed upon the type of three molecules of chloride of am- 
monium (3NH,C1 = N 3 H 12 C1 3 ), in which one-fourth of the hydrogen 
is replaced by formyle and the rest by ethyle ; the composition of this 
chloride is therefore (P 3 (CH)'"(C 2 H 5 ) 9 C1J ; from this compound various 
salts have been obtained containing the corresponding oxide, combined 
with three molecules of the acids, but the hydrate itself has not been 
obtained. 



waaaaaaaaaaataa 



540 AMIDES. 

3P(C a H 5 ) 3 + (CH)'"C1 3 = P,(CH)"(CA)A- 

Triethylphosphiae. OMorofonn. ^^X^™.^ 1 ' 

392. The insight into the constitution of the bases derived from ammonia, which 
has been acquired in the researches detailed above, has induced chemists to endeavour 
to apply the same principles to certain inorganic bases derived from ammonia by the 
action of metallic salts. 

Thus, by the action of (proto) chloride of platinum upon ammonia (see p. 392), 
a compound is obtained which may be regarded as simply PtCl 2 (N"H 3 ) 2 , but when 
this is treated with oxide of silver, the CI is removed in the form of chloride of 
silver, and a caustie alkaline base is separated, which has the formula PtO.(NH 3 ) 2 , 
or rather, viewed upon the type of oxide of ammonium, N 2 H 6 PtO oxide of platam- 
monium. 

By employing ethylamine instead of ammonia there would be obtained 
N 2 H 4 E 2 PtO oxide of ethyloplatammonium. 

When the compound PtCl 2 (NH 3 ) 2 (or rather !N" 2 H 6 Pt.CL. chloride of platammonium) 
is again treated with ammonia, it yields N 2 H 6 Pt.Cl 2 (NH 3 ) 2 , and when this is decom- 
posed with oxide of silver, another caustic alkali is obtained, having the composition 
N 2 H 6 Pt(NH 3 ) 2 H 2 2 which may be regarded as N 2 H 4 Pt(NH 4 ) 2 H 2 2 the hydrate of 
platammon-ammonium (hydrate of diplatosamine) ; it would then become a double 
molecule of hydrate of ammonium (NH 4 HO), in which two atoms of hydrogen are 
replaced by platinum and two by ammonium. 

Very remarkable and beautiful crystalline compounds have also been obtained, 
which are formed after the type of chloride of platammonium, but contain either 
phosphorus, antimony, or arsenic, in place of nitrogen, and ethyle in place of 
hydrogen ; these are — 

Chloride ofplato-triethyl-diphosphonium, . P 2 Pt(C 2 H 5 ) 6 .Cl 2 
,, ,, arsonium, . . As 2 Pt(C 2 H 5 ) 6 .Cl 2 

,, ,, stibonium, . . Sb 2 Pt(C 2 H g ) 6 .Cl 2 

Corresponding salts have also been obtained containing gold in the place of 
platinum, and forming beautiful colourless crystals. 

In some bases, chlorine, bromine, and even nitric peroxide (N0 2 ) have 
been introduced in tne place of hydrogen into the alcohol-radical, but in 
all these cases the basic energy is diminished by such substitution, and in 
some altogether destroyed. 

Thus, in the aniline (phenylamine) series, we have — 

Chloraniline, . . . NH 2 (C 6 H 4 C1), weak base. 



Dichloraniline, 
Trichloraniline, 
Mtraniline, 
Dinitraniline, 



NH 2 (C 6 H 3 C1 2 ), weaker base. 
NH 2 (C 6 H 2 C1 3 ), neutral. 
NH a [C 6 H 4 (N0 2 )], weak base. 
NH 2 [C 6 H 3 (N0 2 ) 2 ], neutral. 



393. Amides. — When oxalate of ammonia (NH 4 ) 2 C 2 4 is subjected 
to distillation, a white, crystalline sparingly soluble substance is obtained, 
which, has been named oxamide, and is represented by the formula 
(NH 2 ) 2 C 2 2 . This substance is derived from the ammonia-salt by the loss 
of 2 molecules of water — 

(NH 4 ) 2 C 2 4 - 2H 2 = (KE 2 ) 2 C 2 3 

and its close relationship to oxalate of ammonia is shown by the circum- 
stance that it is reconverted into that salt, if heated with water in a 
sealed tube to 436° F., or by simply boiling it with, water to which a 
little acid or alkali has been added. 

Oxamide is more readily prepared by decomposing oxalic ether with 
ammonia, when it is obtained as a white crystalline precipitate — 

(C 2 H 5 ) 2 C 2 4 + 2NH 3 = 2C 2 H 5 HO + (NH 2 ) 2 C 2 2 . 

Oxalic ether. Alcohol. Oxamide. 



NITRILES. 



541 



If one of the compound ammonias, such as ethylamine and aniline, be 
employed instead of ammonia, ethlyoxamide and oxanilide are produced — 

2(NH,C S H 5 ) ,, 2C 2 H 5 HO + (NH.C 2 H 5 ) 2 C 2 2 , 

Ethyloxamide. 

(NH.C e H 3 ) 2 C 2 2 . 

Oxanilide. 



(C 2 H 3 ) 2 C 2 4 

Oxalic ether. 

(C 2 H 5 ) 2 C 2 4 



Ethylamine. 

2(NH S .C 6 H 5 ) 

Anihne. 



2C 2 H 5 HO 



Oxamide is the representative of a large class of bodies, known as the 
amides, which may be denned as substances capable of being converted, 
by the assimilation of the elements of water, into the ammonia-salts from 
which they are derived. 

Some other interesting members of this class are here enumerated, 
together with the corresponding ammonia-salts — 



Fonnamide, . 
Acetamide, . 
Butyramide, . 
Benzamide, . 



NH 



2 -C 4 H 7 
C 7 H,0 



Formiate of ammonia, (NH 4 ).CH0 2 

Acetate, (NH 4 ).C 2 H 3 2 

Butyrate, .... (NH 4 ).C 4 H 7 2 
Benzoate, .... (NHi.C 7 H 5 2 



It is evident that these amides may be regarded as derived from ammonia 
by the substitution of a compound group for one of the three atoms of 
hydrogen. 

When binoxalate of ammonia (NH 4 HC 2 4 ) is distilled, at a moderate 
heat, a solid acid substance is left in the retort, which is known as oxamic 
acid, NH 2 .HC 2 3 , and forms soluble crystallisable salts with lime and 
baryta, both which bases yield insoluble salts with oxalic acid. 

When the solution of oxamic acid in water is boiled, it is reconverted 
into the binoxalate of ammonia — 



NH 2 HC 2 3 + 

Oxamic acid. 



H 2 



= NH 4 .HC 2 4 . 

Binoxalate of ammonia. 



Oxamic acid is the representative of a limited class of acids formed in a 
similar manner. 

394. Nitrites. — When oxalate of ammonia is mixed with anhydrous 
phosphoric acid and distilled, it loses 4 molecules of water, leaving 
cyanogen (KH 4 ) 2 C 2 4 - 4H 2 = 2CK 

In a similar manner, benzoate of ammonia yields benzonitrite — 



NH 4 C ; H 5 2 

Benzoate of ammonia. 



2H 2 



C 7 H 5 ^. 

Benzonitrile. 



The new compound is an oil which has a powerful odour of bitter almonds, 
and is reconverted into benzoate of ammonia by boiling with dilute acids 
or alkalies. 

The term nitrite is applied to all similar substances which are derived 
from ammoniacal salts by the loss of 2 molecules of water, and are capable 
of reconversion into those salts. It will be remembered that many of 
these nitriles are identical with the cyanides of the alcohol-radicals. 



Oxalonitrile, NC 

Formonitrile, NCH 

Acetonitrile, NC 2 H 3 

Propionitrile, TSTC 3 H 5 

Benzonitrile, NCJL 



Cy, cyanogen. 
HCy, hydrocyanic acid. 
CH 3 .CN, cyanide of methyle. 
C 2 H 5 .CN " „ ethyle. 



= CJBLCN 



phenyle. 



A by no means numerous class of substances, frequently spoken of as 



542 METAL-AMIDES. 

the imides* are obtained by the action of heat upon the acid ammonia 
salts of certain bibasic acids, by the loss of two molecules of water, thus— 

NH 4 HC 10 H u O 4 - 2H 2 = KH.C 10 H 14 O a . 

Bicamphorate of ammonia. Camphorimide. 

395. If the amides be regarded as immediately derived from ammonia by substi- 
tution, their want of alkaline properties must be ascribed to the introduction of an 
electro -negative radical in place of the hydrogen. 

Thus, if oxalic acid be regarded as H 2 (C 2 2 )0 2 , then oxamide may be viewed as a 
double molecule of ammonia, in which two atoms of hydrogen have been displaced 

by (C 2 2 ); N 2 j(°!° 2 )" 

Again, if benzoic acid and salicylic acid, respectively, be regarded as (C 7 H 5 0)HO 
and (C 7 H 5 2 )HO, then their amides would be represented as — 

Benzamide, N j (^b )' 

Salicylamide, N j ^^^Y 

and it should be possible to procure them from ammonia by processes similar to 
that which furnishes ethylamine, &c. It is found that when chloride of benzoyle is 
heated with ammonia, benzamide is really produced — 

C 7 H 5 0.C1 + 2NH 3 = NH 2 .C 7 H 5 + NH 4 C1. 

Chloride of Benzamide. 

benzoyle. 

But we ought also to be able to carry the substitution farther by displacing the 
remaining hydrogen ; accordingly, when benzamide and salicylamide are heated 
together, ammonia is disengaged, and benzoyl-salicylamide obtained — 



C 7 H 5 C 7 H 5 2 
Nl H + \ H = 
( H ( H 


( C 7 H 5 
N \ C 7 H 5 2 + NH, 
( H 


Benzamide. Salicylamide. 


Benzoyl-salicylamide. 



Amides have even been obtained in which the three atoms of hydrogen in 
ammonia are displaced by different radicals. . 

It is evident that the imides might be regarded as ammonias in which two atoms 
of hydrogen have been replaced by a diatomic radical, thus — 



Camphorimide, N | ^io^iA)" 



and the nitriles, as ammonias in which all the hydrogen has been replaced by a 
triatomic radical, but experimental evidence is scarcely in favour of these views. 

If the amides be really derivatives from ammonia, it would be expected that 
similar bodies should be derived from phosphuretted hydrogen (PH 3 ). An example 
of these is furnished by tribenzoyl-phosphide, P(C 7 H 5 0) 3 , which is obtained by the 
action of chloride of benzoyle upon phosphuretted hydrogen. 

PH 3 + 3(C 7 HgO.Cl) = P(C 7 H 5 0) 3 + 3HC1. 

Chloride of Tribenzoyl- 

benzoyle. phosphide. 

396. Metal-amides. — The possibility of substituting metals for the 
hydrogen in ammonia has only recently been fully established, though it 
had long been known that when potassium and sodium were heated in 
gaseous ammonia, hydrogen was evolved, and potassamide and sodamide 
were produced — 

IS T H 3 + K = NH 2 K + H. 

When potassamide is heated, ammonia is evolved, and tripotassamide 
(M 3 ) produced — 

3(NH 2 K) = NK 3 + 2NH 3 . 

* This designation was originally employed upon the supposition that these bodies con- 
tain the imaginary radical imidogen, NH ; and, in a similar manner, the amides were 
supposed to contain amidogen, NH 2 . 



CHLOROFORM. 543 

If ammoniacal gas be passed into an ethereal solution of zinc-ethyle, 
hydride of ethyle is evolved, and a white amorphous precipitate of 
zincamide separates — 

2NH 3 + (C 2 H 5 ) 2 Zn = (NH 2 ) 2 Zn + 2(C 2 H 5 .H) . 

Zinc-ethyle. Zincamide. ^Ith^lt ^ 

When zincamide is brought in contact with water, it is decomposed with 
evolution of heat, yielding hydrated oxide of zinc and ammonia — 

(NH 2 ) 2 Zn + 2H 2 = 2NH 3 + ZnO.H 2 . 

The decomposing action of zinc-ethyle upon the bases derived from 
ammonia is parallel with that upon ammonia itself. Thus, with 
aniline — 

2(NH 2 .C 6 H 5 ) + (C 2 H 5 ) 2 Zn = (NH) 2 Zri(C 6 H 5 ) 2 + 2(C 2 H 5 H). 

Aniline. Zinc-ethyle. Zinc-phenylimide. Hydride of ethyle. 

When the zinc-phenylimide is treated with water, of course aniline is re- 
produced. 

When diethylamine is heated with zinc-ethyle — 

2N(C 2 H 5 ) 2 H + (C 2 H 5 ) 2 Zn = N 2 (C 2 H 5 ) 4 Zn + 2(C 2 H 5 .H). 

Diethylamine. Diethylzincamine. 

When zincamide is heated above 400° I\, it is decomposed into ammo- 
nia and nitride of zinc (N 2 Zn 3 ), which represents ammonia, in which the 
three atoms of hydrogen are replaced by zinc — 

3(NH 2 ) 2 Zn = K 2 Zn 3 + 4NH 3 . 

Zincamide. *££* 

The nitride of zinc is a grey powder, which is unaffected by a red heat if 
air be excluded. If it be moistened with water, it becomes red hot, 
being decomposed with great violence, according to the equation — 

N 2 Zn 3 + 6H 2 = 2tfH 8 + 3(ZnO.H 2 0) . 

It might be anticipated that if the amides be truly formed after the 
ammonia-type, they should behave towards zinc-ethyle in the same manner 
as ammonia and aniline. 

By heating oxamide with zinc-ethyle, two of its atoms of hydrogen may 
be replaced by zinc — 

N 2 H 4 .C 2 2 + Zn(C 2 H 5 ) 2 = N 2 H 2 Zn.C 2 2 + 2(C 2 H 5 .H). 

Oxamide. Zinc-oximide. 

In a similar manner, acetamide (NH 2 .C 2 II 3 0) is converted into zinc- 
acetimide N 2 H 2 Zn(C 2 H 3 0) 2 . These bodies are reconverted into their cor- 
responding amides and oxide of zinc, when treated with water. 



Derivatives op the Alcohols. 

397. Chloroform. — Among the useful substances prepared from members 
of the alcohol series, chloroform (CHC1 3 ) occupies a prominent position. 

It is prepared by distilling 1 part of alcohol with 6 parts of chloride 
of lime, and 24 parts of water, until about 1J part has passed over; 
the distilled liquid, consisting chiefly of water and chloroform, separates 



544 CHLORAL. 

into two layers, the heavier being chloroform (sp. gr. 1*5). The upper 
aqueous layer having been drawn off by a siphon, the chloroform is 
shaken with oil of vitriol to remove certain volatile oils, which have dis- 
tilled over with it, and as soon as it has risen to the surface of the oil of 
vitriol, it is drawn off and rectified by distillation, until it boils regularly 
at 142° F. 

The chemical change involved in the preparation of chloroform appears 
to consist of two distinct stages, in the first of which the alcohol is con- 
verted into chloral by the action of the chlorine furnished by the chloride 
oflime,C 2 H 6 + Cl 8 - C 2 HC1 3 + 5HC1 ; the hydrochloric acid is, of 

Alcohol. Chloral. 

course, neutralised by the lime. In the second stage the chloral is acted 
upon by the hydrate of lime, which is always present in commercial 
chloride of lime, and is converted into chloroform and formiate of lime, 
2C 2 HC1 3 + CaO.H 2 = Ca(CH0 2 ) 2 + 2CHC1 3 . 

Chloral. Formiate of lime. Chloroform. 

Chloroform is remarkable for its very fragrant odour, and for the power 
of its vapour to produce insensibility to pain, for which purpose it is 
often used in surgical operations. This property is not peculiar to chloro- 
form, but is possessed in different degrees by most other liquids of power- 
ful ethereal odour, such as ordinary ether, bisulphide of carbon, bichloride 
(tetrachloride) of carbon, &c. Chloroform is also used for dissolving 
caoutchouc, which it takes up more readily and abundantly than any 
other liquid, and is employed for extracting the poisonous alkaloids (par- 
ticularly strychnine), when mixed with organic matters. The name chlo- 
roform has been conferred upon this substance on the supposition that it 
contained the radical of formic acid (formyle CH), and it is sometimes 
styled the ter chloride of formyle. This belief is encouraged by its 
behaviour with an alcoholic solution of potash, when it yields formiate of 
potash and chloride of potassium — 

CHC1 3 + 4KHO = KCH0 2 + 3KC1 + 2H 2 0. 

Chloroform. Formiate of potash. 

But the processes by which it may be formed would lead us to regard it 
as a substitution-product ,from marsh-gas (hydride of methyle, CH 3 .H). 
If marsh-gas be diluted with an equal volume of carbonic acid, and to 1 
volume of this mixture at least 1 \ volume of chlorine be added, chloro- 
form is slowly produced, CH 4 + Cl 6 = 3HC1 + CHC1 3 . Chloroform is 
also formed by the action of chlorine upon chloride of methyle — 

CH 3 C1 + Cl 4 = CHC1 3 + 2HC1. 

Wood-spirit (hydrated oxide of methyle) may be employed instead of 
alcohol for the preparation of chloroform. 

If chloroform be distilled in a current of chlorine, it is converted into 
tetrachloride of carbon, CHC1 3 + C1. 2 = CC1 4 + HC1. When chloroform 
is heated with amalgam of potassium, acetylene (C 2 H 2 ) is disengaged, 
which is polymeric with the hypothetical radical formyle CH. 

Bromoform (CHBr 3 ) and Iodoform (CHI 3 ) have no practical interest. 

Chloral (CHC1 3 0), which has been mentioned as resulting from the 
action of chlorine upon alcohol, may be regarded as aldehyde (C 2 H 4 0), in 
which 3 atoms of hydrogen are replaced by chlorine. 

It is prepared by passing thoroughly dried chlorine into absolute 



PERFUME-ETHERS. 545 

alcohol, which, must be placed in a vessel surrounded by cold water at 
the commencement, because the absorption of chlorine is attended by 
great evolution of heat. The passage of chlorine is continued for many 
hours, and when the absorption takes place slowly, the alcohol is gradu- 
ally heated to boiling, the chlorine being still passed in until the liquid 
refuses to absorb it. The principal reaction is C 2 H 6 {alcohol) + Cl 8 = 
C 2 HC1 3 {chloral) + 5HCL* But a secondary reaction takes place 
between the hydrochloric acid and the alcohol ; (C 2 H 5 )HO {alcohol) + 
HC1 = H 2 + (C 2 H 5 )C1 (hydrochloric ether). The water thus formed 
combines with the chloral, forming a heavy oily liquid, which solidifies 
on standing to a white crystalline mass of chloral hydrate, C 2 HC1 3 0.H 2 0. 
To obtain chloral itself, this must be distilled with twice its volume of 
oil of vitriol to remove the water, and with quick-lime to remove the 
hydrochloric acid. 

Chloral is a colourless liquid, with a peculiar pungent odour, exciting 
to tears. Its sp. gr. is 1*5, and it boils at 201° E. It makes a greasy 
mark on paper, and mixes with water, alcohol, and ether. 

When mixed with a small quantity of water, combination takes place, 
with evolution of heat, and the crystallised hydrate is produced. Ex- 
posed to moist air, it absorbs water and forms the hydrate. The chloral- 
hydrate itself readily absorbs water from the air ; it may be sublimed 
without decomposition. 

When kept, chloral suffers a change somewhat resembling that of alde- 
hyde, becoming an opaque white mass, insoluble chloral, insoluble in 
water, alcohol, and ether, and reconvertible into liquid chloral by distil- 
lation. Left in contact with water, it becomes gradually converted into 
chloral hydrate. Chloral is decomposed by solution of potash ; C 2 HC1 3 
(chloral) + KHO = KCH0 2 (formiate of potash) + CHC1 3 (chloroform). 

Chloral hydrate has been lately much used medicinally for procuring 
sleep. The distillation of starch or sugar with hydrochloric acid and 
binoxide of manganese furnishes chloral, together with other products. 

398. Perfume-ethers. — Certain of the compound ethers, formed by the 
combination of oxide of ethyle and its analogues with the acids of the 
acetic series, are employed in perfumery and confectionery. 

Thus, the bidyrate of ethyle, or butyric ether (C 2 ELC 4 II 7 2 ), prepared 
by distilling butyrate of potash with alcohol and sulphuric acid, has a 
decided flavour of pine apples. Acetate of amyle (C 5 H u .C 2 H 3 2 ) has a 
very strong resemblance in taste and smell to the jargonelle pear; it is 
obtained by distilling f ousel oil (hydrated oxide of amyle) with acetate of 
soda and sulphuric acid. 

The valerianate of amyle, which has the flavour of apples, and is known 
as apple-oil, is obtained by distilling fousel oil with sulphuric acid and 
bichromate of potash, when the chromic acid of the latter oxidises one 
portion of the hydrate of amyle (C 5 H n .HO), converting it into valerianic 
acid (C 5 H 10 O 2 ), which then forms the valerianate of amyle (^H^.CslTgOJ. 

399. Aldehydes — Vinic or acetic aldehyde. — It has been already noticed 
(p. 487) that a considerable loss of alcohol has occasionally taken place in 
the manufacture of vinegar, in consequence of the formation of aldehyde 

* An intermediate compound of chloral and alcohol, G 2 HC1 3 0.C 2 H P 0, also appears to be 
formed. It is a solid crystalline body, fusing at 115° F., boiling at 234° F., and difficultly 
soluble in water, which distinguishes it from chloral hydrate. Heat decomposes it into 
chloral and alcohol. 

2 M 



546 ALDEHYDE. 

(C 2 H 4 0) instead of acetic acid (C 2 H 4 2 ) by a partial oxidation of the alcohol. 
In order to prepare aldehyde in quantity, alcohol is distilled with sulphuric 
acid and binoxide of manganese, or with sulphuric acid and bichromate 
of potash, or it may be oxidised by chlorine in the presence of water. 

Three parts of binoxide of manganese in fine powder are introduced into a retort, 
and a mixture of 3 parts of sulphuric acid and 2 of water, which has been allowed to 
cool, is poured upon it. 2 parts of alcohol (sp. gr. - 85) are then added, the mixture 
very gently heated, and the vapours condensed in a Liebig's condenser, or in a 
worm (fig. 214) supplied with iced water. If bichromate of potash be employed, 3 
parts of the salt are introduced into the retort with 2 parts of alcohol. The retort is 
placed in cold water to moderate the action, and a mixture of 4 parts of sulphuric 
acid with three times its volume of water is allowed to flow slowly into the retort. A 
very gentle heat may be applied when the action has moderated. 

In these processes the alcohol is oxidised according to the equation — 
QftO + O = C 2 H 4 + H 2 0. 

Alcohol. Aldehyde. 

In the first process the oxygen is derived from the binoxide of manganese, 
leaving sulphate of manganese (MnO.$0 3 ) in the retort ; in the second 
process, the chromic acid of the bichromate furnishes the oxygen, sulphate 
of chromium (Cr 2 3 .3S0 3 ) being formed. As might be expected, a portion 
of the alcohol is oxidised to a higher degree, and converted into acetic 
acid (C 2 H 4 2 ), so that some acetic ether comes over together with the 
aldehyde. Another product, acetal, is also found in the distillate, which 
has the composition C 6 H 14 2 , and may be regarded as resulting from the 
union of ether, formed by a secondary action of the sulphuric acid upon 
the alcohol, with aldehyde ((C 2 H 5 ) 2 O.C 2 H 4 0). 

By redistilling the aldehyde with an equal weight of fused chloride of calcium in 
a gently heated water-bath, it may be freed from most of the water and alcohol, which 
are left behind in the retort, the boiling point of aldehyde being only 67°'8 F. After 
rectification, it may be separated from the acetic ether and acetal, by taking advan- 
tage of its property of combining with ammonia to form a compound which is 
insoluble in ether ; the rectified aldehyde is mixed with twice its volume of ether, 
placed in a bottle surrounded by ice, and saturated with gaseous ammonia (p. 120), 
when white needle-like crystals of aldehyde ammonia (NH 3 .C 2 H 4 0) are deposited. 
By distilling this compound with diluted sulphuric acid, and condensing the vapour 
in a thoroughly cooled receiver, pure aldehyde is obtained, from which the last por- 
tions of water may be removed by standing over fused chloride of calcium and a final 
distillation. 

Aldehyde may be recognised by its peculiar acrid odour, which affects 
the eyes, as well as by its volatility and inflammability. It absorbs 
oxygen from air even at the ordinary temperature, and is gradually con- 
verted into acetic acid. Its attraction for oxygen enables it to reduce the 
salts of silver to the metallic state, and a characteristic test for aldehyde 
consists in adding a little nitrate of silver and a trace of ammonia ; on 
heating, the silver is deposited as a mirror on the sides of the test-tube. 
In contact with hydrate of potash, aldehyde undergoes decomposition, 
yielding a brown substance (resin of aldehyde) and a solution of acetate 
and formiate of potash. By distilling a mixture of these two salts, alde- 
hyde may be reproduced — 

KC 2 H 3 2 + KCH0 2 - K 2 O.C0 2 + C 2 H 4 0. 

Acetate of Formiate of .,.. , 

potash. potash. Aldehyde. 

These reactions lend some support to the opinion, that aldehyde should 
be represented as being framed upon the model of a molecule of hydrogen 
(IIH), in which the place of one atom of hydrogen is occupied by acetyle 



ALDEHYDES. 



547 



(C 2 H 3 0), the hypothetical radical of acetic acid. For if formiate of potash 
be distilled with caustic potash, it yields carbonate of potash and two 
atoms of hydrogen, KCH0 2 + KHO = K 2 O.C0 2 + HH ; and if acetate of 
potash be employed instead of the hydrate, aldehyde is obtained instead 
of hydrogen — 

KCH0 2 + K(C 2 H 3 0)0 = K 2 O.C0 2 + (C 2 H 3 0)H . 

On this view it is easy to explain the tendency of aldehyde to undergo 
oxidation, forming acetic acid, just as hydrogen is converted into water 
by oxidation. 



Type. — Molecule of water, H 2 
Acetic acid, (C 2 H 3 0)H0 . 



Type. — Molecule of hydrogen, H.H 
Aldehyde (hydride of ace- 
tyle), C 2 H 3 O.H 

As might be anticipated, it is found that when vapour of aldehyde is 
passed over heated caustic potash (mixed with lime) it yields acetate of 
potash and hydrogen, C. 2 H 3 O.H + KHO = H.H + K(C 2 H 3 0)0. 

By the action of potassium, the atom of hydrogen may be displaced 
from the aldehyde, and the compound (C 2 H 3 0)K obtained. 

In contact with water and sodium amalgam, aldehyde combines with 
the nascent hydrogen, and produces alcohol. Chlorine displaces three- 
fourths of the hydrogen from aldehyde, producing chloral^ C 2 CLHO, 
which has been already noticed as yielding chloroform when acted on by 
alkalies. 

Perfectly pure aldehyde cannot be kept for any length of time, even in 
sealed tubes, since it becomes converted into metaldehyde and elaldehyde, 
which have the same composition as aldehyde, but differ widely from it 
in properties, metaldehyde being a crystalline solid, and elaldehyde a 
liquid, boiling at 201° F. The true formula of elaldehyde would appear 
to be C 6 H 12 3 for the specific gravity of its vapour is 4 - 52, or three times 
that of aldehyde vapour (1 -53). Metaldehyde is reconverted into alde- 
hyde when heated to 400° F. in a sealed tube. 

When aldehyde is treated with a saturated solution of bisulphite of 
soda (Na 2 O.H. 2 0.2S0 2 ), it forms a crystalline compound, which is soluble 
in water, but insoluble in the saline solution, and contains the elements of 
2 molecules of the aldehyde and 1 molecule of the bisulphite. 

If the view above referred to be correct, which represents aldehyde as 
the hydride of acetyle (the radical of acetic acid), each of the acids 
belonging to the acetic series would be expected to have a corresponding 
aldehyde. Accordingly, just as acetate of lime, when distilled with for- 
miate of lime, yields acetic aldehyde, so valerianic, cenanthic, and caprylic 
aldehydes may be obtained by distilling the corresponding lime-salts 
with formiate of lime. 

The chief aldehydes of this series which have at present been examined 



Acetic aldehyde, 
Propionic aldehyde, 
Butyric aldehyde, 
Valeric aldehyde, 



C 4 H 8 Q 
CJL ft Q 



* It will he remarked that these aldehydes are polymeric with the compound ethers 
formed hy their acids ; thus, acetic aldehyde is polymeric with acetic ether, for — 

2C 2 H 4 = C 2 H 5 .C 2 H 3 2J 
hut the sp. gr. of aldehyde vapour (1-53) is only half that of acetic ether vapour (3-06). 



548 ACETONES OR KETONES. 



(Enanthic aldehyde, 



C 7 H 14 

C 8 H 16 

CiaMoaO 



Caprylic aldehyde, 
Kutic aldehyde, 
Euodic aldehyde, 
Laurie aldehyde, 

The radicals corresponding to acetyle, which may be regarded as asso- 
ciated with hydrogen in these aldehydes, have not, for the most part, been 
isolated ; a substance having the same composition as butyryle (C 4 H 7 0), 
the supposed radical of butyric acid (C 4 H 8 2 ), has, however, been obtained 
from that acid by an indirect process. 

Acetic, propionic, and butyric aldehydes have been found among the 
products of the oxidising action of a mixture of binoxide of manganese 
and sulphuric acid upon fibrine, albumen, and caseine. 

Valeric aldehyde is obtained, like acetic aldehyde, by distilling the 
corresponding alcohol (amyle-alcohol, C 5 H 12 0) with sulphuric acid and 
bichromate of potash. 

Capric (rutic), euodic, and lauric aldehydes are found in essential oil of 
rue. The higher aldehydes of the series are not so easily oxidised as 
those containing a lower number of carbon atoms. 

When an aldehyde is heated with one of the bases derived from 
ammonia by the substitution of an alcohol-radical for one atom of hydro- 
gen, the other two atoms of hydrogen of the ammonia are replaced by the 
diatomic hydrocarbon of the aldehyde ; thus — 

2NHAH„ + 2C 7 H 14 = 2H 2 + N 2 (0 6 H n ) 2 (C 7 H u )/- 

Amylamine. aldehyde^ Di-oenanthylene-di-amylamine. 

This reaction has been recommended for the determination of the 
replaceable (or typical) hydrogen in organic bases. 

400. Acetones. — If the lime salts of the acids of the acetic series, 
instead of being distilled with formiate of lime, as for the preparation of 
the aldehydes, be distilled alone, or with quick-lime, a series of homo- 
logous products is obtained, each of which is isomeric with the aldehyde 
of the series next below it in the table, though totally different from that 
aldehyde in properties. 

Thus, by distilling acetate of lime with lime, the liquid acetone or 
pyro-acetic spirit (C b H t .O) is obtained, which has been already noticed 
among the products of the distillation of wood — 

Ca(G 2 H 3 2 ) 2 = CaO.CO, + C 3 H 6 . 

Acetate of lime. Acetone. 

Acetone has the same composition as propionic aldehyde.* By similar 
processes the following acetones (or ketones, as they are frequently called) 
have been obtained : — 



Acetone, 


. C 3 H 6 


Propione, 


. C 5 H 10 O 


Butyrone, 


. C 7 H 14 


Valerone, 


C 9 H 18 



These substances are allied, in some of their properties, to the aldehydes, 
especially in forming crystalline compounds with bisulphite of soda. 
Hence many chemists have been led to believe that they are composed, 

* Aldehyde is slowly formed by the action of chromic acid upon ethylene, and acetone 
may be obtained in a similar manner from propylene. 



OIL OF BITTEE ALMONDS AN ALDEHYDE. 549 

like the aldehydes, after the model of a molecule of hydrogen, but that 
in the acetones the radicals of the corresponding acids are associated, not 
with an atom of hydrogen, but with the hydrocarbon radical of the next 
lower alcohol. Thus, the acetone of the acetic series (C 3 H 6 0) would be 
composed of the radical acetyle (C 2 H 3 0) associated with methyle (CH 3 ), 
and this view of its constitution is supported by the formation of acetone, 
when chloride of acetyle is acted upon by zinc-methyle — 

2(C. 2 H 3 0.C1) + (CH 3 ) 2 Zn = 2(C 2 H 3 O.CH 3 ) + ZnCl 2 . 

Chloride of acetyle. Zinc-methyle. Acetone. 

In a similar manner, chloracetene (resulting from the action of chloro- 
carbonic acid on aldehyde) yields acetone when acted on by methylate of 
soda (sodium-methyle-alcohol) — 

(C 2 H 3 )C1 + (CH 3 )NaO = KaCl + C 2 H 3 O.CH 3 . 

Chloracetene. Methylate of soda. Acetone. 

Further corroboration is obtained by distilling a mixture of equivalent 
quantities of acetate and valerianate of potash, when an acetone is obtained, 
which contains valeryle (C 5 H 9 0), associated with methyle (CH 3 ) — 

KC 2 H.A + KC 5 H 9 2 = K 2 O.C0 2 + C 5 H 9 O.CH 3 . 

Acetate of potash. Valerianate of potash. 

It will be remembered that when acetate of potash is distilled with 
caustic potash, it yields marsh-gas by a precisely parallel reaction — 

KC 2 H 3 2 + KHO = K 2 O.C0 2 + H.CH 3 . 

Acetate of potash. Marsh-gas. 

Acetone may also be prepared by distilling sugar with eight times its 
weight of quick-lime, when it is accompanied by another liquid, metacetone, 
C 6 H 10 O, which differs from acetone in being insoluble in water. When 
this liquid is heated with bichromate of potash and sulphuric acid, it is 
oxidised and converted into metacetonic or propionic acid, HC 3 H 5 2 , 
which may also be produced by the oxidation of acetone. 

401. The description above given of the properties of aldehyde will 
have recalled those of some of the essential oils containing oxygen. Thus, 
essential oil of bitter almonds (C 7 H 6 0), when exposed to air, absorbs 
oxygen, and is converted into benzoic acid (C 7 H 6 2 ), just as aldehyde 
(C 2 H 4 0) passes into acetic acid (C 2 H 4 2 ). Moreover, oil of bitter almonds 
forms a crystalline compound with bisulphite of soda, similar to that 
formed by aldehyde, and its conversion into this compound is sometimes 
resorted to in order to obtain the pure oil. 

In constitution, also, oil of bitter almonds (hydride of benzoyl e, 
C 7 H 5 O.H) closely resembles aldehyde (hydride of acetyle, C 2 H 3 O.H), 
and just as the latter may be obtained by distilling acetate of potash with 
formiate of potash, so benzoic aldehyde (oil of bitter almonds) may be 
obtained from benzoate of potash. 

K(C 7 H 5 )0 + KCH0 2 = K 2 O.C0 2 + C 7 H 5 O.H. 

Benzoate of potash. Formiate of potash. Benzoic aldehyde. 

Oil of bitter almonds is produced, together with some aldehydes of the 
acetic series of acids (p. 547), when certain albuminous bodies are oxi- 
dised by sulphuric acid and binoxide of manganese. 

When benzoic aldehyde is acted on by an alcoholic solution of caustic 



550 POLYATOMIC ALCOHOLS. 

potash, an oily liquid is obtained, which stands in the same relation to 
benzoic aldehyde as alcohol bears to acetic aldehyde. 

2(C 7 H 5 O.H) + KHO = K(C 7 H 5 0)0 + C 7 H 8 0. 

Benzoic aldehyde. Benzoate of potash. Benzoic alcohol. 

The conversion of bitter almond oil into benzoic alcohol may also be 
effected by the action of water and amalgam of sodium (to furnish nascent 
hydrogen) ; whereas, by treatment with zinc and hydrochloric acid, it is 
converted into hydrobenzoine (C 7 H 7 0). 

The hydrochloric ether of benzoic alcohol, C 7 H 7 C1, is sometimes called 
chloride of benzyle, the radical benzyle, C 7 H 7 , being supposed to have the 
same relation to the benzoic series as ethyle has to the acetic series. By 
the action of ammonia upon chloride of benzyle, benzylamine, NH 2 (C 7 H 7 ), 
and tri-benzylamine, N(C 7 H 7 ) 3 , have been obtained ; the former is isomeric 
with toluidine, but is by no means identical with it ; for benzylamine is 
a liquid having basic properties far more powerful than those of tolui- 
dine, and it is very readily soluble in water, which dissolves but little of 
the latter base. 

The benzoic acetone or benzone (C l3 H 10 O) has been obtained by the distil- 
lation of benzoate of lime. It is often called benzophenone, being regarded 
as an association of benzoyle with phenyle, C 7 H 5 O.C 6 H 5 ; for when dis- 
tilled with potash, it yields benzoate of potash and benzole (hydride of 
phenyle) — 

C 7 H 5 O.C,H 5 + KHO = K(C 7 H 5 0)0 + C 6 H 5 .H. 

Benz6phenone. Benzoate of potash. Benzole. 

Oil of cinnamon (p. 471) or hydride of cinnamyle (C 9 H 7 O.H) is the alde- 
hyde of cinnamic acid (C 9 H 8 2 ) ; and essential oil of cummin contains 
the aldehyde (C 10 H U O.H) of cuminic acid (C 10 H ]; ,O 2 ), and yields cuminic 
alcohol (C 10 H 14 O) when treated with alcoholic solution of potash. Oil of 
spiraea or hydride of salicyle (C 7 H 5 2 .H) is the aldehyde of salicylic acid 
(C 7 H fi 3 ). Hydride of anisyle (C 8 H 7 2 .H), obtained by the oxidation of 
oil of aniseed, is the aldehyde of anisic acid (C 8 H 8 3 ), and of anisic 
alcohol (C 8 H 10 O). These aldehydes allow their associated atom of hydro- 
gen to be displaced by chlorine more readily than the aldehydes of the 
acetic series, to form chlorides of their respective radicals (p. 470). 

Glycol — Polyatomic Alcohols. 

402. It has been already shown (p. 518) that alcohol may be con- 
veniently regarded as composed after the fashion of a molecule of water 
(H 2 0) in which half the hydrogen has been displaced by ethyle (C 2 H 5 ) ; 
according to this view alcohol is represented by the formula H(C 2 H 5 )0 ; 
and it is a monatomic alcohol, for it contains the monatomic radical 
(C 2 H_)'. But if, following the same plan, a diatomic radical, such as 
ethylene (C 2 H 4 )*, were to displace half the hydrogen in water, the dis- 
placement could not be effected in less than two molecules of water 
(H 4 2 ), and a diatomic altohol would result. 

Glycol (C. 2 H 6 2 ) is the representative of the diatomic alcohols, and may 
be regarded as two molecules of water, in which half the hydrogen is 
replaced by ethylene (H 2 (C 2 H 4 ) // 2 ). It is obtained by the action of 
biniodide of ethylene (formed by the direct union of olefiant gas with 
iodine) upon acetate of silver — 

2(AgC 2 H 3 2 ) + (C f HJI 2 - 2AgI 4- (C 2 H 4 )".2C 2 H 3 2 . 

Acetate of silvpr. ethylene? Binacetate of glycol. 



GLYCOL. 551 

The binacetate of glycol thus formed corresponds to the acetic ether 
((C 2 H 5 )C 2 H 3 2 ) derived from common alcohol; but since ethylene is 
diatomic, it displaces the hydrogen in two molecules of acetic acid. When 
the result of this action is distilled, the binacetate of glycol passes over 
as a colourless liquid, which sinks in water, and boils at 365° F.* 

Glycol can be obtained from the binacetate by digesting it with hydrate 
of potash for some time at 360° F., and distilling, when the glycol passes 
over, its boiling point being 387° F. It is a colourless liquid, having a 
sweet taste, whence it derives its name (yXvKvs, sweet). Like common 
alcohol, it mixes with water in all proportions, and may be distilled 
without decomposition. It also gives an inflammable vapour, and has 
never been frozen ; but, unlike alcohol, it is heavier than water (sp. gr. 
1-125), and does not mix with ether, though alcohol dissolves it readily. 

Glycol is also capable of forming the monacetate of glycol, C 2 H 4 HC 2 H 3 2 , 
and a remarkable compound has been obtained known as acetobutyrate 
of glycol C 2 H 4 .C 2 H 3 2 .C 4 H 7 2 . 

The action of hydrochloric acid upon glycol does not perfectly corres- 
pond with its action upon common alcohol, for instead of yielding a chlo- 
ride of ethylene, it gives a compound of hydrochloric acid with oxide of 
ethylene. 

H^Oft/O, + HC1 = (Oft)" '6.HC1 + H 2 0. 

Glycol. Chlorhydrine of glycol. 

By decomposing this compound with potash, the oxide of ethylene 
(C 2 H 4 ) // is obtained, as a colourless liquid, which boils at 56° F., 
and is, therefore, not identical with aldehyde (which boils at 68° F.), 
though it has the same composition. It is obvious that glycol might 
be represented as (C 2 H 4 )' / O.H 2 0, the hydrated oxide of ethylene, and 
this view is favoured by the circumstance that glycol may be formed 
by heating the oxide of ethylene with water in a sealed tube ; but, on 
the other hand, when glycol is treated with chloride of zinc, to de- 
hydrate it, ordinary aldehyde (C 2 H 4 0), and not the ethylenic oxide, is 
produced. 

By the action of pentachloride of phosphorus upon glycol, the bi- 
chloride of ethylene, or Dutch liquid, is obtained — 

H 2 (C 2 HX0 2 + 2PC1 5 = (C.H/'Cl, +~2HC1 + 2P0C1 3 . 

„. . Bichloride of Oxychloride of 

Wyco ethylene. phosphorus. 

It will be observed that this equation is the exact counterpart of 
that which represents the action of pentachloride of phosphorus upon 
water, substituting diatomic ethylene for monatomic hydrogen — 

H 2 (H 2 ) ,/ 2 + 2PCL = (H 2 ) ,/ C] 2 + 2HC1 + 2P0C1 3 . 

Sodium acts upon glycol in the same manner as upon ordinary alcohol, 
but in consequence of the di-atomic character of glycol, the reaction 
takes place in two stages, producing, successively, mono-sodium glycol, 
HN"a(C 2 H 4 ) // 2 and di-sndium glycol, Na 2 (C 2 H 4 ) // 2 , both which are solid. 

When glycol is exposed to the action of oxygen in the presence of 
platinum-black, or when it is cautiously oxidised with nitric acid, it 
becomes converted into glycolic acid, C 2 H 4 3 , which bears the same rela- 

* A liquid isomeric with binacetate of glycol, but boiling at 336° F., is obtained by heat- 
ing aldehyde in a sealed tube with acetic anhydride. 



552 



LACTIC SERIES OF ACIDS. 



tion to it as acetic acid bears to common alcohol, as will be evident from 
the following equations :* — 



H(C 2 H 5 ).0 

Alcohol. 

H 2 (C 2 H/.0 2 

Glycol. 



+ 2 = H(C 2 H 3 0).0 + H 2 



Acetic acid. 



+ 2 = H 2 (C,H 2 0)".0 2 + 



H 2 



Glycolic acid. 



in which the change consists, in both cases, in the substitution of for 
H. 2 in the radical of the alcohol, acetic acid being formed upon the type 
of a molecule of water (H 2 0) in which H is replaced by C 2 H 3 0, and gly- 
colic acid upon the type of two molecules (H 4 2 ), in which H 2 are replaced 
by C 2 H 2 0. If the oxidation with nitric acid be carried farther, the 
remainder of the hydrogen in this last radical is replaced by oxygen, and 
oxalic acid is produced — 



H 3 (C. 2 H 2 0)".0 2 

Glycolic acid. 



+ o = 



H 2 (C 2 2 )".0 2 + 

Oxalic acid. 



H 2 0. 



By the action of nascent hydrogen upon oxalic acid, the in the radi- 
cal may be again displaced by H 2 , so that glycolic acid is reproduced. 

Glycolic acid forms a syrupy liquid which resembles lactic acid, but is 
distinguished from it by being precipitated with acetate of lead. Unlike 
oxalic acid, glycolic is a monobasic acid, only one atom of its hydro- 
gen being replaceable by a metal. Glycolic acid is found together with 
oxalic acid among the products of the action of nitric acid upon alcohol 
in the preparation of fulminate of mercury, which is easily accounted for 
by the connection between alcohol and ethylene, which is best exhibited 
by writing the formula of alcohol (C 2 H 4 ).H 2 0. 

Glycolic acid is the first member of a series of homologous acids, of 
which the most important is lactic acid, these acids standing in the same 
relation to the glycols in which the members of the acetic series stand to 
the alcohols. 

Lactic Series of Acids. 



Name. 


Formula. 


Source. 


Glycolic acid, 


C 2 H 4 3 


Oxidation of glycol and of alcohol. 


Lactic acid, . . 


C 3 H 6 3 


Fermentation of cane and milk sugars. 


Butylactic acid, 


C 4 H 8 3 


Oxidation of butyl -glycol. 


Valerolactic acid, 


C 5 H 10°3 


( Decomposition of bromo-valerianic 
I acid with oxide of silver. 


Leucic acid, . 


^6^12^3 


Action of nitric acid on leucine. 



It will be observed that these acids are intermediate, with respect to 
the number of atoms of oxygen which they contain, between the acetic 
and the oxalic series of acids ; thus — ■ 



Acetic acid, 
Glycolic ,, 
Oxalic ,, 



C 2 HA 
C 2 HA 

C,H„0. 



Propionic acid, 
Lactic „ 

Malonic, 



<W>. 

<W>, 
C.H.0,. 



* The aldehyde of glycol, glyoxal, C ? H„0 2 , is found among the products of the decom- 
position of nitrous ether in contact with water. 



FORMATION OF LEUCIC FROM OXALIC ACID. 553 

These three series of acids, therefore, present a relation to each other 
similar to that between the three series of alcohols, represented by — 

Vinic alcohol, . . C 2 H 6 

Glycol, . . . C 2 H 6 2 
Glycerine, . . - C 3 H 8 3 . 

Just as acetic and glycolic acids are formed by the oxidation of alcohol 
and glycol, so the oxidation of glycerine by nitric acid furnishes glyceric 
acid,CJlfi^ 

The transition from the oxalic series to the lactic series of acids has 
been effected in the case of leucic acid, which has been artificially formed 
from oxalic acid, by converting it into oxalic ether, and acting upon this 
with zinc-ethyle, when leucic ether is obtained, from which leucic acid is 
easily prepared. The reaction is rendered intelligible if the two acids be 
thus formulated — 

Oxalic acid, . . C 2 H 2 4 

Leucic „ . . C 2 H 2 (C 2 H 5 ) 2 3 , . 

from which it appears that, neglecting intermediate stages, the zinc 
of the zinc-ethyle removes an atom of oxygen from the oxalic acid, 
leaving ethyle in its stead, so that leucic acid may be regarded as dietli- 
oxalic acid, or oxalic acid containing two of ethyle instead of one of 
oxygen. If oxalate of methyle be substituted for oxalate of ethyle in this 
experiment, leucate of methyle, CH 3 .C 6 H u 3 is obtained, and when this 
is decomposed by baryta, and the leucate of baryta treated with sulphuric 
acid, fine crystals of leucic acid are obtained, which are readily soluble in 
water, alcohol, and ether, and sublime slowly at the ordinary tempera- 
ture.* By the reaction between iodide of methyle, oxalate of methyle, 
and amalgamated zinc, dimethoxalic ac^,C 2 H 2 (CH 3 ) 2 3 , has been obtained, 
which may be regarded as oxalic acid containing two of methyle in the 
place of an atom of oxygen. Dimethoxalic acid is isomeric with butylactic 
or acetonic acid (C 4 H 8 3 ) ; it crystallises in prisms resembling those of 
oxalic acid, which may be sublimed at 122° F., and volatilise slowly even 
at the ordinary temperature. 

From the other hydrocarbons of the olefiant gas series (p. 508), glycols 
may be prepared by processes similar to that which furnishes ethylene- 
glycol. Thus propylene (C 3 H 6 ) yields propylene-glycol, H 2 (C 3 H 6 )".0 2 ; 
butylene (C 4 H 8 ), butylene-glycol, H 2 (C 4 H 8 ) // .0 2 ; amylene (C 5 H 10 ), amy- 
lene-glycol, H 2 (C 5 H 10 ) // .O 2 ; it is a very remarkable circumstance that the 
boiling points and specific gravities of these liquids decrease as the com- 
plexity of the formula increases, which is quite contrary to ordinary 
experience; thus amylene-glycol (C 5 H 12 2 ) has the sp. gr. 0-987, and 
boils at 351° F., whilst propylene-glycol (C 3 H 8 2 ) has the sp. gr. 1*051, 
and boils at 371° F. 

When propylene-glycol is slowly oxidised, it is converted into lactic 
acid, exactly as glycol is converted into glycolic acid — 

H 2 (C 3 H 6 r.0 2 + 2 = H 2 (C 3 H 4 0y.0. 2 + H 2 0. 

Propylene-glycol. Lactic acid. 

The difference between the diatomic character of glycol and the mona- 
tomic character of ordinary alcohol, is strongly marked in their behaviour 

* It is said that this leucic acid, though closely resembling that obtained from oxalic 
ether, is not identical with it. 



554 WATER-TYPE VIEW OF POLYATOMIC ALCOHOLS. 

with, the organic acids, for whilst the monatomic alcohol yields (with 
monobasic acids) only one series of compound ethers derived from one 
molecule of acid, the diatomic glycol yields two series derived respectively 
from one and two molecules of acid ; thus we have monacetate of glycol 
(C 2 H 4 )".H(C ? H 3 0)0 2 and diacetate of glycol, (C 2 H 4 )^(C 2 H 3 0) 2 .0 2 . In the 
last series, it is not necessary that the two molecules should consist 
of the same acid, as may be seen in the acetobutyrate of glycol, 
(C 2 H 4 )' / .C 2 H 3 O.C 4 H 7 0,0, 

Just as polyatomic ammonias are formed upon the type of several 
molecules of ammonia, so polyatomic alcohols may be produced by the 
substitution of compound radicals for hydrogen in a multiple alcohol 
type. Thus, by heating glycol in a sealed tube with oxide of ethylene, 
di-ethylene-trialcohol, H 2 (G 2 H 4 )'' 2 3 , is produced, which is formed upon 
the type of three molecules of alcohol, H 3 (C 2 H 5 ) 3 3 . In a similar manner, 
tri-ethylene-tetralcohol, H 2 (C 2 H 4 ) 3 // 4 , is formed upon the quadruple 
alcohol type, H 4 (C 2 H 5 ) 4 4 . 

It will be seen hereafter that glycerine (C 3 H 8 3 ), the sweet principle 
of oils and fats, is a triatomic alcohol, formed upon the type of three 
molecules of water (H 6 3 ), in which half the hydrogen is replaced by 
the triatomic radical, (C 3 H 5 ) /// , glyceryle, the formula of glycerine being 
H s (C 3 H 5 )'"0 3 . 

It is easy to convert a diatomic into a monatomic alcohol; for example, 
if the chlorhydrine of glycol be treated with amalgam of sodium in the 
presence of water, it becomes converted into ordinary (monatomic) 
alcohol — 

C 2 H 5 C10 + H 2 + Na 2 = C 2 H 6 + NaHO + KaCL 

Chlorhydrine AlcohoL 

of glycol. 

The relation of the alcohols to water as their primary type is here 
exhibited — 

TT -V 

Type, one molecule of water, H 2 = tt [ 

TT \ 

Vinic alcohol, C 2 H 6 = (CHY i® 

TT \ 

Type, two molecules of water, H 4 2 = tt 2 > 2 

Glycol, C 2 H 6 2 = (C 2 H 4 V}° 2 

Type, three molecules of water, H 6 3 = H 2 V 3 

hJ 

H„ 



Diethylene-trialcohol, C 4 H 10 O 3 = (C,H,)" V 3 

(<W) 
TT ) 
Glycerine, C 3 H 8 3 = (Cfil)"' j ° 3 

TT ) 
Type, four molecules of water, H b 4 = a I 4 

TT ) 

Triethylene-tetralcohol, C 6 H 14 4 = ,^ H 2 w/ > 4 

The compounds formed by the action of acids upon these alcohols would 
then be represented by such formulae as the following : — 



ACETATES — ACETONE. 555 

Acetic ether, .... 'Wj' 1 

Monacetate of glycol, . . ^A'J'j} 1 2 

Diacetate of glycol, . . . (^V I Q 2 

(C 2 H 3 6)') 
Acetobutyrate of glycol, (C 4 H 7 0)' V 2 

• (CH 4 yj 

Monacetine, ^^H V" \ °* 

Diacetine, ...... ( ° 2 ^^ } 3 

Triacetine, ^ftU} * 

ACETIC ACID— THE EATTY ACID SEEIES. 

403. The most useful of the acids belonging to the acetic series (see 
p. 507) is acetic acid itself, the preparation of which has been already de- 
scribed. 

Many of its salts are extensively employed in the arts. Acetate of 
alumina is used as a mordant by the dyer and calico-printer. Acetate of 
lead or sugar of lead, Pb(C 2 H 3 2 ) 2 3Aq„, is prepared by dissolving litharge 
(PbO) in an excess of acetic acid, when the solution deposits prismatic 
crystals of the acetate which are easily dissolved by water and alcohol. 

Goulard's extract, or tribasic acetate of lead, is prepared by dissolving 
litharge in solution of acetate of lead; it may be obtained in needle-like 
crystals, which have the composition Pb(C 2 H 3 2 ). 2 2PbO.H 2 0. 

Verdigris, or basic acetate of copper, Cu(C 2 H 3 2 ) 2 .Cu0.6H 2 0, is pre- 
pared by piling up sheets of copper with layers of fermenting husks of 
grapes (the marc of the wine-press), when the oxide of copper, formed at 
the expense of the oxygen of the air, combines with the acetic acid fur- 
nished by the oxidation of the alcohol. 

Acetone (C 3 H 6 0) is obtained by the destructive distillation of acetate 
of lime — 

Ca(C 2 H 3 2 ) 2 = CaO.C0 2 + C 3 H 6 

Acetate of lime. Acetone. 

a decomposition which possesses some general interest since the lime-salts 
of the other acids of the acetic series yield ketones in a similar manner 
(seep. 548). 

The acetone thus obtained is an ethereal liquid lighter than water, boil- 
ing at 133° E., and burning with a luminous name. It is easily miscible 
with water, but separates when hydrate of potash is added, rising to the 
surface. 

Under the action of chlorine, acetic acid loses an atom of hydrogen, 
taking chlorine in its place, and forming chloracetic acid, H.CJE 2 C10 2 ;* 
and if the action be promoted by sun-light, trichloracetic acid may be 
formed, H.C 2 C1 3 2 , which may be crystallised. This latter acid has a 
peculiar interest on account of its being concerned in the production of 
acetic acid from inorganic materials, which was one of the first examples 
of the actual synthesis of organic compounds. 

* Dichloracetic acid, H.C ? HC1 2 2 , has also been obtained. 



556 ACETIC ANHYDRIDE. 

The synthesis of acetic acid has been effected by the action of chloro- 
carbonic acid upon marsh-gas, when hydrochloric acid and acetic oxy- 
chloride are formed — 

CH 4 + COCl 2 = (C a H,0)Cl + HC1. 

Acetic oxy- 
chloride. 

When the acetic oxychloride is decomposed by water, acetic acid is pro- 
duced — 

(C 2 H 3 0)C1 + H 2 = H(C 2 H 3 0)0 + HC1. 

This appears to be an example of a general method of synthesis of the 
volatile fatty acids, starting from the marsh-gas hydrocarbons derived from 
them ; thus, hydride of amyle, C 5 H 12 , treated in a similar manner, yields 
caproic acid, HC 6 H n 2 . 

404. Anhydrides of organic acids. — Acetic anhydride. — The course of 
investigation by which, of late years, much light has been thrown upon 
the true constitution of acetic acid, and therefore of many other organic 
acids, is of a very instructive character. The strongest acetic acid which 
can be prepared (see p. 461) is known as glacial acetic acid, from its crys- 
tallising in icy leaflets at about 55° F. This acid has the composition 
C 2 H 4 2 , and may be regarded as a molecule of water in which half the 
hydrogen is replaced by the hypothetical radical acetyle, C 2 H 3 . 

When this acid is distilled with terchloride of phosphorus, a colourless, 
very pungent liquid is obtained, which is commonly spoken of as acetic 
oxychloride, C 2 H 3 0C1 — 

2H(C 2 H 3 0)0 + PC1 3 = HC1 + HP0 2 +• 2(C 2 H 3 0)C1. 

Acetic acid. Phosphorous Acetic of oxychloride. 

acid. 

That this acetic oxychloride (or chloride of acetyle) really bears a very 
close relationship to acetic acid, is shown by the action of water, which 
acts with explosive violence and reproduces the acetic acid — 

(C 2 H 3 0)C1 + H 2 = H(C g H 3 0)0 + HC1. 

Acetic oxychloride. Acetic acid. 

If caustic potash be allowed to act upon the chloride of acetyle — 

(C 2 H 3 0)C1 + KHO = H(C 2 H 3 0)0 + KC1. 

But if acetate of potash (KC 2 H 3 2 ) be employed instead of caustic 
potash — 

(C 2 H 3 0)C1 + K(C 2 H 3 0)0 = C 2 H 3 O.C 2 H 3 0.0 + KC1. 

Acetic oxychloride. Acetate of potash. Acetic anhydride. 

Acetic anhydride has also been obtained by heating dry acetate of lead 
or of silver with bisulphide of carbon in a sealed tube to about 320° F. 
for several hours, the tube being occasionally opened to relieve the pres- 
sure of the carbonic acid evolved— ■ 

2Pb(C 2 H 3 0) 2 2 + CS 2 = 2PbS + C0 2 + 2(C 2 H 3 0) 2 0. 

The acetic anhydride is a neutral oily liquid which may be distilled off 
in the above experiment. Its smell recalls that of acetic acid, but affects 
the eyes strongly. It sinks in water, but dissolves slowly, with evolution 
of heat and formation of hydrated acetic acid.* 

* If acetic anhydride be heated with an excess of binoxide of barium, it yields acetate of 
baryta, carbonic acid, and methyle gas (p. 513). 

2(C 2 H 3 0) 2 + Ba0 2 = Ba(C 2 H 3 2 ) 2 + 2CH 3 + 2C0 2 . 
By absorbing the carbonic acid with potash, the pure methyle gas is easily obtained. 



FORMIC ACID. 557 

The most convincing proof that this anhydride is really formed after 
the type of a molecule of water, is obtained by acting upon the acetate of 
potash with the benzoic instead of the acetic oxychloride — 

(C 7 H 5 0)C1 + K(C 2 H 3 0)0 = KC1 + C 7 H 5 O.C 2 K,0.0. 

Benzoic Acetate of Benzo-acetic 

oxychloride. potash. anhydride. 

and the true nature of this double anhydride is seen by its conversion into 
a mixture of hydrated benzoic and acetic acids when left in contact with 
water. 

By methods similar to that employed for acetic acid, the anhydrides of 
many other organic acids may be obtained — 

Peroxides of organic radicals. — Considerable support has been offered 
to that view of the constitution of the organic acids, which represents 
them as composed after the type of water, by the discovery of certain com- 
pounds which bear the same relation to the anhydrides as peroxide of 
hydrogen bears to water. 

When binoxide of barium is acted on by hydrochloric acid, chloride of 
barium and peroxide of hydrogen are formed — 

Ba0 2 + 2HC1 = BaCl 2 + H 2 2 . 

If binoxide of barium be acted on by benzoic oxychloride (chloride of 
benzoyle), the products are chloride of barium and benzoic peroxide 
(peroxide of benzoyle) — 

Ba0 2 + 2(C 7 H 5 0)C1 = BaCl 2 + (C 7 H 5 0) 2 2 . 

The benzoic peroxide may be obtained in fine crystals from its ethereal 
solution, but like the peroxide of hydrogen, it is easily decomposed at 
about 212° F. with explosive violence. By the action of alkalies, it is 
resolved into benzoic acid and oxygen, just as peroxide of hydrogen yields 
water and oxygen — 

(C 7 H 5 0) 2 2 + 2KHO = 2K(C 7 H 5 0)0 + 2 + H 2 . 

By acting upon acetic anhydride with binoxide of barium, the acetic 'per- 
oxide (or peroxide of acetyle) is obtained — 

* Ba0 2 + 2(C 2 H 3 0) 2 = Ba(C 2 H 3 2 ) 2 + (C 2 H 3 0) 2 2 . 

Acetate of baryta." Acetic peroxide. 

The acetic peroxide is an oily liquid, insoluble in water, and exploding 
with great violence when heated. It has the powerful oxidising pro- 
perties which would be expected from its chemical resemblance to peroxide 
of hydrogen. 

405. Formic acid (H.CH0 2 ) is regarded with great interest by the 
chemist, from its occurring both in the animal and vegetable kingdoms, 
and from the ease with which it may be artificially obtained. This acid 
is found in the leaves of stinging-nettles, and was originally obtained by 
distilling the red ants {formica rufa), whence it derives its name. 

It has long been prepared in laboratories by the oxidation of various 
organic substances, particularly by distilling starch with binoxide of 
manganese and sulphuric acid. Another more modern process, which 
yields it more abundantly, consists in distilling dried oxalic acid with 
enough glycerine to cover it, when it is resolved into carbonic acid and 
formic acid — 

H 2 C 2 4 (Oxalic ucid) — TLCH0. 2 (Formic acid) + C0 2 . 



558 FURFUROLE — BUTYRIC ACID. 

The glycerine appears to act by producing an unstable compound with, 
the formic acid (analogous to the stearinesand acetines, see p. 565), which 
is afterwards decomposed. The solution of formic acid thus obtained con- 
tains 75 per cent, of true hydrated formic acid. If dried oxalic acid be 
heated in the aqueous formic acid, and the solution allowed to crystallise, 
the oxalic acid retains the water, and when the liquid is decanted from 
the crystals and distilled, pure formic acid is obtained, and may be 
crystallised at a low temperature. 

But the most remarkable method of obtaining formic acid is that in 
which it is formed from inorganic materials. When formic acid is heated 
with strong sulphuric acid, it is resolved into water and carbonic oxide, 
HCH0 2 = H 2 + CO. 

It might, therefore, be expected to be reproducible by the combination 
of those two substances, and accordingly, if moistened caustic potash be 
heated for some hours to 212° F. in a flask filled with carbonic oxide, the 
gas is absorbed, and formiate of potash produced, from which the formic 
acid may be obtained by distillation with diluted sulphuric acid — 

KHO 4- CO = KCH0 2 {Formiate of potash). 

This is a far simpler example of the synthesis of an organic compound 
from inorganic materials than that of acetic acid above referred to, and 
since the carbonic oxide may be prepared by heating carbonate of baryta 
with metallic iron, this method of synthesis is quite independent of any 
organic source of carbon. Ethylate of sodium, NaC 2 H 5 0, also absorbs 
carbonic oxide, forming etliyl-formiate of sodium NaC(C 2 H.)0 2 isomeric 
with propionate of soda, a little of this salt being also formed. 

In properties, formic acid bears a great general resemblance to acetic 
acid, but has a more powerful action upon the skin when in the concen- 
trated form. It is employed in the manufacture of one of the blue colours 
derived from coal-tar. 

Furfurole (C 5 H 4 2 ), or oil of ants, accompanies the formic acid obtained by dis- 
tilling amylaceous matters with binoxide of manganese and sulphuric acid. It is 
prepared in quantity by distilling bran (freed from starch and gluten by steeping in 
a cold weak solution of potash) with half its weight of sulphuric acid (previously 
diluted with an equal bulk of water), a current of steam being forced through the 
mixture ; the furfurole distils' over with the water, from which it may be separated 
by fractional distillation. It is a colourless oily substance, smelling of bitter almonds, 
becoming brown when exposed to the air, and but slightly soluble in water. Strong 
sulphuric acid dissolves it to a purple liquid, from which water precipitates it un- 
changed. Furfurole resembles the aldehydes in its property of reducing oxide of 
silver, and in forming a crystalline compound with bisulphite of soda. It is con- 
vertible by oxidation into pyromucic acid (C 5 H 4 3 ), the acid obtained by distilling 
the mucic acid derived from the oxidation of gum or milk-sugar. The systematic 
name for furfurole, therefore, would be pyromucic aldehyde. 

Just as oil of bitter almonds (benzoic aldehyde), when acted on by ammonia, is 
converted into hydrobenzamide, so furfurole yields furfuramide — 

3C 7 H 6 + 2KE 8 = C 21 H ]8 N 2 + 3H 2 
Oil of bitter almonds. Hydrobenzamide. 

3C 5 H 4 2 + 2NH 3 = C 16 H M N,0, + 3H 2 . 
Furfurole. Furfuramide. 

And, just as hydrobenzamide, when boiled with solution of potash, yields the iso- 
meric base amarinc or benzoline (C 21 H ]8 N 2 ), so furfuramide, when boiled with potash, 
gives furfurine (C 15 H 12 N 2 3 ), which is isomeric with it. 

Butyric acid (HC 4 H 7 2 ) is found not only in rancid butter, but in the 
juice of muscular flesh, and is a frequent product of fermentation. 



SYNTHESIS OF ACIDS OF THE ACETIC SERIES. 559 

Indeed, the best mode of obtaining this acid consists in exciting fermen- 
tation in sugar by contact with cheese ; the liquid soon becomes acid, in 
consequence of the formation of lactic acid (the acid of sour milk), and if 
it be neutralised from time to time with chalk, this fermentation continues 
until the whole is converted into a pasty crystalline mass of lactate of 
lime Ca(C 3 H 5 3 ) 2 . The formation of lactic acid from sugar becomes in- 
telligible on comparing the formulae — 

1 molecule of cane-sugar, C 12 H 22 O u 

4 molecules of lactic acid, C^H^O^ . 

After a time the mass becomes more fluid, at the same time evolving 
bubbles of gas, which contain carbonic acid and hydrogen, for the lactate 
of lime is undergoing a fermentation, by which it is converted into buty- 
rate of lime — 

2Ca(C 3 H 5 3 ) 2 + H 2 = Ca(C 4 H 7 2 ) 2 + CaO.C0 2 + 3C0 2 + H 8 . 

Lactate of lime. Butyrate of lime. 

By distilling the butyrate of lime with dilute hydrochloric acid, an aqueous 
solution of butyric acid is obtained, and on saturating this with chloride 
of calcium, the acid collects as an oily layer upon the surface. It is 
remarkable for its powerful odour of rancid butter.* 

Synthetical for •mation of acids of the acetic series. — By a very remark- 
able process of substitution, butyric acid has been derived from acetic 
acid. When sodium is heated with acetic ether, it is gradually dissolved, 
and the liquid solidifies on cooling, to a crystalline mass containing, 
among other products, sodacetic ether, or acetic ether in which one atom 
of the hydrogen has been displaced by sodium. The reaction appears to 
take place in two stages — 

(1) 3(C 2 H 5 .C 2 H 3 0.0) + Na 4 = 3(C 2 H 5 .Na.O) + Na(C 2 H 3 0) 3 . 

Acetic ether. Sodium-alcohol. Sodium-triacetyle. 

(2) C 2 H 5 NaO + C 2 H 5 .C 2 H 3 0.0 = C 2 H 5 .H.O + C 2 H 5 .C 2 (H 2 ¥a)0.0 . 

Sodium-alcohol. Acetic ether. Alcohol. Sodacetic ether. 

By digesting the sodacetic ether with iodide of ethyl for several hours in 
a close vessel, at 212° F., the atom of sodium is exchanged for ethyle, and 
ethacetic ether, or butyric ether, is produced — 

C 2 H,C 2 (H 2 Na)0 2 + C 2 H 5 I = mi + C 2 H,C 2 H 2 (C 2 H 5 )0 2 . 

Sodacetic ether. Iodide of ethyL Ethacetic or butyric ether. 

From this ether the ethacetic acid, C 2 H 3 (C 2 H 5 )0 2 , has been prepared and 
found to be identical with butyric acid, C 4 H 8 2 . 

The connection thus established between butyric acid and the ethyle 
series helps to explain the production of that acid in the fermentation 
of sugar. 

But butyric ether has also been obtained by another process of substitu- 
tion, which affords a proof that the same substance may be correctly 
represented by two distinct rational formulge. 

The substitution of sodium for hydrogen in acetic ether may extend to 
two atoms of hydrogen, and if the disodacetic ether so produced be 
digested with iodide of methyle, butyric ether is obtained — 

C 2 H 5 .C 2 (HNa 2 )0 2 + 2CH 3 I = 2NaI + C 2 H 5 .C 2 H(CH 3 ) 2 2 . 

Disodacetic ether. Iodide of methyle. Dimethacetic or butyric ether. 

* Butyric acid and some of its homologues (as valerianic and caproic) appear to be present 
in the perspiration of the skin, and to cause the disagreeable odour of close rooms. 



560 VALEEIANIC ACID. 

So that butyric acid may be regarded, according to the method by which 
it is produced, either as ethacetic acid, formed from acetic acid by the 
substitution of an equivalent of ethyle for one of hydrogen, or as dimeth- 
acetic acid, resulting from the substitution of two equivalents of methyle 
for two of hydrogen. 

When disodacetic ether is acted on by iodide of ethyle, it yields dieth- 
acetic ether — 

C 2 H 5 .C 2 (HNa,)0 2 + 2C 2 H 5 I = 2NaI + C 2 H 5 .C 2 H(C 2 H.) 2 2 . 

Disodacetic ether. Iodide of ethyle. Diethacetic ether. 

This ether has an odour resembling peppermint, and its composition is 
the same as that of caproic ether, C 2 H 5 .C 6 H n 2 ; but the diethacetic acid 
prepared from it, though isomeric with caproic acid (C 6 H 12 2 ), is not 
identical with it. 

The acid next in the series, cenanthic (HC 7 H 13 2 ), may be obtained 
from the ether produced by the action of iodide of amyle upon sodacetic 
ether — 



C 2 H 5 .C 2 (H 2 Na)0 2 + C 5 H n I = Nal + C 2 H 5 .C 2 H 2 (C 5 H n )0 2 . 

Sodacetic ether. ainvle° Amyl-acetic ether. 

From this ether, the amyl-acetic acid, H.C 2 H 2 (C 5 H u )0 2 , which appears 
to be identical with cenanthic acid, has been obtained. 

These reactions help to explain the production of several of the alco- 
hols corresponding to the acetic series of acids, during the fermentation 
of grape husks (marc of the wine-press). 

Among the products of the action of sodium and ethylic iodide upon acetic ether, 
is a liquid having the composition C 8 H 14 3 , which, when distilled with alkaline 
bases, yields ethylated acetone, C 3 H 5 (C 2 H 5 jO, isomeric with the acetone of propionic 
acid (propione, C 5 II 10 O) — 

C 8 H 14 3 + BaO.H 2 = C 5 H 10 O + C 2 H 6 + BaO.C0 2 . 

Ethylated Alcohol 

acetone. Alcohol. 

Another liquid produced by the action of ethylic iodide upon disodacetic ether has 
the composition C 10 H 18 O 3 , which furnishes diethylated acetone, C 3 H 4 (C 2 H 5 ) 2 0, when 
distilled with baryta water — 

C 10 H 18 O 3 + BaO.H 2 = C 7 H 14 + C 2 H 6 + BaU.CO,. 
Diethylated Alcohol 
acetone. AiconoL 

Diethylated acetone is a liquid smelling of camphor, and boiling at 280° F. It is 
isomeric with butyrone, which boils at 290° F., and with cenanthic aldehyde or 
cenanthole, which boils at 312° F. 

By treating acetic ether with sodium and methylic iodide, the corresponding 
methylated acetones may be obtained. 

Methylated acetone, C 3 H 5 (CH 3 )0, has the odour of chloroform, and is identical with 
the ethyl-acetyle, C 2 H 3 O.C 2 H 5 , obtained by the action of zinc-ethyle upon chloride 
of acetyle. 

Dimethylated acetone, C 3 H 4 (CH 3 ) 2 0, has an odour of parsley. 

Valerianic acid (H.C 5 H 9 2 ) derives interest from the circumstance 
that some of its salts, particularly the valerianate of zinc, are used medi- 
cinally. 

This acid is found in valerian root, and in the berries of the guelder- 
rose. It is one cause of the peculiar odour of decaying cheese, and of 
whale and seal oils. 

Artificially, it is best obtained by distilling f ousel oil (amylic alcohol, 
C 5 H 12 0) with sulphuric acid and bichromate of potash, when the oxygen 



CHEMISTEY OF SOAP. 561 

of the chromic acid converts part of the amylic alcohol into valerianic 
acid — 

C 5 H 12 (Fousel oil) + 2 — C 5 H 10 O 2 (Valerianic acid) + H 2 . 

The distilled liquid is really a mixture of valerianic acid and valeria- 
nate of amyle (C 5 H n .C 5 H 9 2 ), but when treated with caustic potash, the 
latter is decomposed, yielding fousel oil and valerianate of potash. 

C 6 H u -C 5 H 9 2 + KHO = C^rHO + K.C 5 H 9 2 . 

Valerianate of amyle. Fousel oil. Valerianate of potash. 

By distilling the valerianate of potash with sulphuric acid, the valeri- 
anic acid is obtained as an oily liquid of very remarkable odour, which 
recalls that of butyric acid. 

406. The separation of the volatile acids belonging to the acetic series 
is a problem which frequently presents itself to the chemist, and is 
effected by a very instructive process of partial saturation, founded upon 
the principle, that when a mixture containing two acids with different 
boiling points is partially neutralised by an alkali and distilled, the more 
volatile of the two acids {i.e., that having the lower boiling point) will 
pass over, whilst the other remains in combination with the alkali. 

In applying this method, for example, to a mixture of valerianic acid 
(boiling at 347° F.) and butyric acid (boiling at 315° F.), in unknown 
proportions, the liquid would be divided into two equal parts, one of 
which would be exactly neutralised with potash, and then distilled to- 
gether with the other half. If there were just enough valerianic acid to 
combine with the potash, pure valerianate of potash would be left in the 
retort, and the more volatile butyric acid would pass over. If there were 
more valerianic acid than would be required to combine with the potash, 
the excess of that acid would distil over, together with the butyric acid, 
whilst valerianate of potash alone would be left in the retort. By distill- 
ing this salt with sulphuric acid, the pure valerianic acid would be ob- 
tained, and the separation of the rest of the valerianic from the butyric 
acid would be effected by one or two repetitions of the process. 

If the valerianic acid present in the mixture were not in sufficient 
quantity to combine with the potash added, then butyrate of potash, as 
well as valerianate, would be left in the retort, and pure butyric acid would 
distil over. By distilling the mixture of valerianate and butyrate of 
potash with sulphuric acid, a mixture of the two acids would be obtained 
which would require a repetition of the process. 

In any case, it will be observed that this process must yield one of the 
acids in a state of purity. 

The same principle applies to the separation of three or more volatile 
acids, but the process involves, of course, a greater number of distillations. 

407. Soap. — The manufacture of soap affords an excellent instance of 
a process which was in use for centuries before anything was known of 
the principles upon which it is based, for it was not till the researches of 
Chevreul were published, in 1813, that any definite ideas were entertained 
with respect to the composition of the various fats and oils from which 
soaps are made. 

The investigations of Chevreul are conspicuous among the labours 
which have contributed in so striking a manner to the rapid advancement 
of chemistry during the present century ; undertaken when the chemistry 

2 N 



562 ACTION OF ALKALIES ON FATS. 

of organic substances had scarcely advanced beyond the dignity of an art, 
when the principles of classification were almost entirely empirical, and 
hardly any research had been' published which could serve as a model, 
these researches reflect the remarkable sagacity and accuracy of their 
author. 

The sense of our obligation to this eminent chemist is further increased, 
when we remember that the ultimate analysis of organic substances was 
then effected by a very difficult and laborious process, whilst the doctrine 
of combining proportions was so imperfectly understood, that it could afford 
but little assistance in confirming or interpreting the results of analysis. 

All soaps result from the action of the alkalies upon the oils and fats. 

In the manufacture of soap, potash and soda are the only alkalies em- 
ployed, the former for soft, the latter for hard soaps. 

The fatty matters employed by the soap-maker are chiefly tallow, palm 
oil, cocoa-nut oil, and kitchen stuff, for hard soaps, and seal oil and whale 
oil for soft soaps. 

In the manufacture of hard soap, the alkali is prepared by boiling a 
solution of carbonate of soda (soda-ash) with lime to remove the carbonic 
acid — 

Na 2 O.C0 2 + CaO.H 2 = CaO.C0 2 + Na 2 O.H 2 (or 2KaHO) , 

the clear solution of hydrate of soda, or soda-ley, being drawn off from 
the insoluble carbonate of lime. 

The tallow is at first boiled with a weak soda-ley, because the soap 
which is formed is insoluble in a strong alkaline solution, and would 
envelope and protect a quantity of undecomposed tallow ; in proportion 
as the saponification proceeds, stronger leys are added, until the whole of 
the grease has disappeared. In order to separate the soap which is 
dissolved, advantage is taken of the insolubility of soap in solution of salt ; 
a quantity of common salt being thrown into the boiler, the soap rises to 
the surface, when the spent ley is drawn off from below, and the soap 
transferred to iron moulds that it may harden sufficiently to be cut up 
into bars. 

In order to understand the chemistry of this process, it is necessary to 
know that tallow is a mixture of two fatty substances, one of which, 
stearine* (C 57 H 110 O 6 ), is solid, and the other, oleine (C 57 H 104 O 6 ), liquid, 
the quantity of stearine being about thrice that of oleine. 

When these fats are acted upon by soda, they undergo decomposition, 
furnishing stearic and oleic acids, which combine with the soda to form 
soap, whilst a peculiar sweet substance, termed glycerine, passes into 
solution ; the nature of the decomposition in each case will be understood 
from the following equations : — 

C 3 H,(C, 8 H 35 0) 3 .0 3 + 3(NaHO) = 3Na(C 18 H 36 0)0 + C 3 H s 3 

Stearine. Stearate of soda. Giycerine. 

C 3 H 5 .(C l8 H, 3 0) 3 .0 3 + 3(NaHO) = 3Na(C 18 H, 3 0)0 + C H H s 3 , 

Oleine. Oleate of soda. Glycerine. 

so that the soap obtained by boiling tallow with soda is a mixture of the 
stearate of soda with about a third of its weight of oleate of soda, and 
from 20 to 30 per cent of water. 

Palm oil is composed chiefly of palmitine (C 51 H 98 6 ), a solid fat which 

* H-eap, tallow. 



STEAEIC AND OLEIC ACIDS. 563 

is resolved by boiling with soda into palmitate of soda (palm oil soap) and 
glycerine — 

C 3 H,(C 16 H 3l O)A + 3(NaHO) = 3Na(C 16 H 81 0)0 + C s H 8 3 . 

Palmitine. Palmitate of soda. Glycerine. 

In the fish oils, the predominant constituent is oleine,, so that when 
boiled with hydrate of potash, they yield oleate of potash (KC 18 H 33 2 ), 
which composes the chief part of soft soap. 

Castile soap is made from olive oil, which contains oleine and a solid fat 
known as margarine. The latter appears to be really composed of palmi- 
tine and stearine, so that the Castile soap is a mixture of oleate, palmitate, 
and stearate of soda. 

The peculiar appearance of mottled soap is caused by the irregular dis- 
tribution of a compound of the fatty acid with oxide of iron, which 
arranges itself in veins throughout the mass. If the soap contained too 
much water, so as to render it very fluid when transferred to the moulds, 
this iron compound would settle down to the bottom, leaving the soap 
clear, so that the mottled appearance is often regarded as an indication 
that the soap does not contain an undue proportion of water ; it is imi- 
tated, however, by stirring into the pasty soap some sulphate of iron and 
a little impure ley containing sulphide of sodium, so as to produce the 
dark sulphide of iron by double decomposition.* 

In the manufacture of yellow soap, in addition to tallow and palm oil, 
a considerable proportion of common rosin (see p. 465) is added to the soap 
shortly before it is finished. 

Soft soap is not separated from the water by salt like hard soap, but is 
evaporated to the required consistency. 

Transparent soaps are obtained by drying hard soap, dissolving it in hot 
spirit of wine, and pouring the strong solution into moulds after the greater 
part of the spirit has been distilled off. 

Silicated soap is a mixture of soap with silicate of soda. 

Glycerine soap is prepared by heating the fat with alkali and a little 
water to about 400° F. for two or three hours, and running the mass at 
once into moulds. It is, of course, a mixture of soap and glycerine. 

The proportion of water in soaps is very variable, some specimens con- 
taining between 70 and 80 per cent. The smallest proportion is about 30 
per cent. 

The theory of saponification, stated above, has received the strongest 
confirmation within the last few years, by the synthetic production of the 
fats from glycerine and the fatty acids formed in their saponification. 

Preparation of the fatty acids. — All the soaps, when mixed with acids, 
undergo decomposition, their alkalies combining with the acid added, 
whilst the fatty acids separate either in the solid form (in the case of stearic 
and palmitic acids), or as an oily liquid (in the case of oleic acid). Thus, 
if soap obtained by boiling tallow with soda be dissolved in hot water, 
and mixed with an excess of tartaric acid, an oil rises to the surface which 
concretes into a buttery mass on cooling. This mass, composed of stearic 
and oleic acids, is submitted to pressure in order to separate the greater 
part of the liquid oleic acid, and the stearic acid which is left is purified 
by crystallisation, first from alcohol, and afterwards from ether. 

Stearic acid is thus obtained in transparent colourless plates which have 

* A soap which contains much more than 30 per cent, of water is said not to admit of 

mottling. 



564 DECOMPOSITION OF FATS BY SULPHURIC ACID. 

the composition HC 18 H 35 2 ; they are, of course, insoluble in water, but 
dissolve in hot alcohol, the solution being acid to test-papers. 

All the stearates are insoluble in water except those of the alkalies, so 
that if a solution of common soap (containing stearate of soda) be mixed 
with a solution of lime or magnesia, a stearate of lime or magnesia is 
separated in the insoluble form, and it will be remembered that this 
decomposition of soap is produced by the action of hard waters (page 44). 

408. Candles. — Since tallow fuses at about 100° F., and stearic acid 
not below 159°, it is evident that, independently of other considerations, 
the latter would be better adapted for the manufacture of candles, for such 
candles would never soften at the ordinary atmospheric temperature in 
any climate, and would have much less tendency to gutter in consequence 
of the excessive fusion of the fuel around the base of the wick. The 
gases furnished by the destructive distillation of stearic acid in the wick 
of the candle burn with a brighter flame than those produced from tallow. 
Accordingly the manufacture of stearine (or more correctly, stearic acid) 
candles* has now become a very important and instructive branch of 
industry. 

The original method of separating the stearic acid from tallow on the 
large scale, consisted in mixing melted tallow with lime and water, and 
heating the mixture for some time to 212° by passing steam through it. 
The tallow was thus converted into the insoluble stearate and oleate of 
lime, which was drained from the solution containing the glycerine, and 
decomposed by sulphuric acid. The mixture of stearic and oleic acids 
thus obtained was cast into thin slabs, which were packed between pieces 
of cocoa-nut matting, and well squeezed in a hydraulic press, which forced 
out the oleic acid, leaving the stearic and palmitic acids in a fit state for 
the manufacture of candles. 

The separation of. the solid fatty acids from tallow and other fats may 
also be effected by the action of sulphuric acid, a process extensively 
applied in this country to palm and cocoa-nut oils. These fats are mixed 
in copper boilers with about one-sixth of their weight of concentrated sul- 
phuric acid, and heated by steam to about 350° F. for some hours, when 
part of the glycerine is converted into sulphoglyceric acid (C 3 H 8 3 .S0 3 ), 
and the remainder is decomposed by the sulphuric acid, carbonic and sul- 
phurous acids being disengaged, whilst a dark-coloured mixture of palmitic, 
stearic, and oleic acids is left. A part of the oleic acid becomes converted 
in this process into elaidic acid, which has the same composition, but 
differs from oleic acid in fusing at about 113° F., so that the amount of 
solid acid obtained by this process is much increased. This mixture is 
well washed from the adhering sulphuric and sulphoglyceric acids, and 
transferred to a copper still into which a current of steam is passed, which 
has been raised to about 600° F. by passing through hot iron pipes. 
These fatty acids could not be distilled alone without decomposition, but 
under the influence of a current of steam they pass over readily enough, 
leaving a black pitchy residue in the retort, which is employed in making 
black sealing-wax, and for other useful purposes. 

The distilled fatty acids are broken up and pressed between cocoa-nut 
matting to remove the oleic add. 

One great advantage of this process, which is commonly, though incor- 
rectly, styled the saponification by sulphuric acid, is its allowing the con- 

* Composite candles are made of a mixture of stearic and palmitic acids; 



SYNTHESIS OF NATURAL FATS. 565 

version of the worst kinds of refuse fat into a form fit for the manufacture 
of candles ; thus the fat extracted from bones in the manufacture of glue, 
and that removed from wool in the scouring process, may be turned to 
profitable account. 

It will be remarked that in this process the palmitic, stearic, and oleic 
acids are formed from the palmitine, stearine, and oleine existing in the 
fats, by the assimilation of the elements of water and the subsequent 
separation of glycerine, just as in the ordinary process of saponification 
by means of alkalies. 

Strictly speaking, the action appears to consist of two stages ; for when 
concentrated sulphuric acid is allowed to act upon the natural fats in the 
cold, it combines with each of their ingredients, forming the acids known 
as sulphostearic, sulphopalmitic, sulpholeic, and sulphoglyceric, which are 
soluble in water, though not (with the exception of the last) in water 
containing sulphuric acid. 

The second stage consists in the decomposition of the sulpho-fatty acids 
by the high temperature in contact with steam, the sulphoglyceric acid 
having been in great measure decomposed into secondary products before 
the distillation is commenced. 

Within the last few years, the extraction of the solid acids from the 
natural fats has been effected by a process known as saponification by 
steam, which allows the glycerine also to be obtained in a pure state. It 
is only necessary to subject the fat, in a distillatory apparatus, to the 
action of steam, at a temperature of about 600° F., to cause both the 
fatty acids and the glycerine to distil over; the former may be separated 
as usual into solid and liquid portions by pressure, whilst the glycerine, 
which is obtained in aqueous solution below the layer of fatty acids, is 
concentrated by evaporation and sent into commerce as a very sweet 
colourless viscid liquid. The saponification of palmitine, for instance, by 
steam, would be represented by the equation — 

C 3 H 5 .(C 16 H 31 2 ) 3 + 3H 2 = 3(H.C 16 H 31 2 ) + C 3 H 8 3 . 

Palmitine. Palmitic acid. Glycerine. 

409. In the artificial formation of natural fats, this change has been 
reversed, for by heating 3 molecules of stearic, palmitic, or oleic acid with 
1 molecu]e of glycerine, in a sealed tube, for several hours, to about 
500° F., 3 molecules of water are ehniinated, and stearine, palmitine, or 
oleine is produced. 

By a similar process, compounds have been formed from glycerine with 
one and two molecules of the fatty acids, so that we are acquainted, in the 
stearine series, for example, with- 







Stearic acid Glycerine. 




Monostearine, . 


C 2 iH 42 4 = 


C 18 H 36 2 + C 3 H 8 3 - 


- H 2 


Bistearine, . 


C 39 H 76 5 = 


2(C 18 H 36 2 ) + C 3 H 8 3 - 


- 2H 2 


Terstearine, . 


> C 57 H 11(A = 


3CC 18 H 36 2 ) + C 3 H 8 3 - 


- 3H 2 



The last representing stearine as it exists in the natural fats. 

Nor is it only with the fatty acids, properly so called, that glycerine will 
furnish glycerides, as these bodies are termed, similar compounds having 
been obtained with acetic and benzoic acids. 

The hydrogen-acids are also capable of acting upon glycerine in a similar manner. 
Thus, when glycerine (C 3 H 8 3 ) is acted on by hydrochloric acid, an oily liquid, 
chlorhydrine (C 3 H 7 2 C1), is obtained, the glycerine having combined with 1 molecule 
of hydrochloric acid, and 1 molecule of water having been separated. 

DicMnrliydrine (0 3 H 6 0C1 2 ) results from the union of glycerine with 2 molecules of 



566 GLYCERINE. 

hydrochloric acid, and separation of 2 molecules of water ; whilst, to form trichlorhy- 
drine (C 3 H 5 C1 3 ), 3 molecules of hydrochloric acid are taken up, and 3 molecules of 
water removed. 

By the action of oxide of silver, in presence of water, the chlorhydrines may be 
reconverted into glycerine. The examination of these chlorhydrines has pointed 
out the method of effecting the conversion of a triatomic alcohol (glycerine) into a 
diatomic alcohol (glycol), for if chlorhydrine be acted on by sodium dissolved in 
mercury, in the presence of water, it is converted into the glycol of propylene — 

C 3 H 7 2 C1 + H 2 + Na 2 = C 3 H 8 2 + NaHO + NaCl. 
Chlorhydrine. Propyl-glycol. 

This tendency of glycerine to form compounds with the acids, the 
formation of which is attended (like that of the ethers from alcohol) with 
separation of the elements of water, has led chemists to look upon glyce- 
rine as an alcohol — a view which is also supported by its combining with 
sulphuric and phosphoric acids to form sulplwgly eerie (C 3 H 8 3 .S0 3 ) and 
phosphogly eerie acids, just as alcohol forms sulphovinic and phosphovinic 
acids. A compound has even been obtained, which is believed to stand 
to glycerine in a relation similar to that which ether bears to alcohol ; the 
formula of this glyceric ether, as it is called, is C 6 H 10 O 3 , differing from 2 
molecules of glycerine (C 6 H 16 6 ) by the elements of 3 molecules of water. 

The formation of stearine from stearic acid and glycerine would then 
be quite analogous to that of acetic ether, for example, from acetic acid 
and alcohol, as will be seen by comparing the two equations — 
H.C 2 H,0 2 + C 2 H 5 .HO = C 2 H 5 .C 2 H,0 2 + H 2 

Acetic acid. Alcohol. Acetic ether. 

3(H.C 18 H 36 O s ) + C 3 H,HA = a,H s .3C 18 H i5 2 + 3H 2 . 

Stearic acid. 6l \^^ Stearine. 

The only difference between the two reactions is, that in the latter, 
3 molecules of acid are concerned, and 3 molecules of water are formed. 
This circumstance, taken together with some other features of glycerine, 
has induced those chemists who consider alcohol as formed upon the type 
of a molecule of water, to look upon glycerine as derived in a similar 
manner from 3 molecules of water, in which half the hydrogen is replaced 
by the triatomic radical, glyceryle (C.JIJ"' ; thus — 

Type . . . g } Type gs J 3 

Alcohol . C f?s Glyceric alcohol, (C 3 H 5 )'" 
H ) or glycerine, H 3 

Ether . . £ 2 g 5 J Glyceric ether, [^H 5 )"' 

410. Glycerine is obtained on the small scale by boiling olive oil with 
litharge and water, until the stearic, oleic, and palmitic acids are converted 
into their lead-salts (lead plaster), which are insoluble, whilst the glyce- 
rine, together with a little oxide of lead, passes into solution. The lead is 
precipitated by hydrosulphuric acid, and the filtered liquid concentrated 
by evaporation. 

The chief uses of glycerine as an application to the skin, and a remedy 
in cases of deafness, depend upon its oily consistency, and its want of 
volatility, which preserves surfaces to which it is applied in a moist and 
supple condition. 

Glycerine cannot be distilled alone without decomposition, though it has 
been seen to be capable of distillation in a current of highly heated steam. 
When decomposed by distillation, it evolves very irritating vapours of 
acroleine (C 3 H 4 Q), which is a constant product of the destructive distilla- 



ACIDS OF THE ACHYLIC SEKIES. 



567 



tion of fats containing glycerine, and gives rise to the peculiar disgusting 
odour of a smouldering tallow candle ; composite candles, being made of 
stearic and palmitic acids (without glycerine) do not emit this odour of 
acroleine when blown out. 

Acroleine is best obtained in the pure state by distilling glycerine 
with anhydrous phosphoric acid, which removes 2 molecules of water 
(C 3 H 8 3 — 2H 2 = C 3 H 4 0). It is a colourless liquid, distinguished by its 
intensely irritating vapour, which affects the eyes very strongly. From a 
chemical point of view it is interesting, as being the aldehyde of the allyle 
series (see p. 474), and, therefore, another link connecting that series with 
glycerine. By treatment with oxide of silver, acroleine is converted into 
acrylic acid (C 3 H 4 2 ), bearing the same relation to acroleine (C b H 4 0) that 
acetic acid (C 2 H 4 2 ) bears to ordinary aldehyde (C 2 H 4 0). The iodide of 
allyle and allylic alcohol have been already noticed (p. 474). 

The allyle series, therefore, is perfectly parallel with the ethyle series, 
and it seems very probable that allylic alcohol is a member of a homo- 
logous series of alcohols having the general formula C n H 2n O, with a series 
of acids corresponding to the acetic series, but having the general formula 
C n H 2n _ 2 2 , of which the following members are known : — 

Acrylic Series of Acids. 



Acid. 


Formula. 


Source. 


Acrylic . . 


C 3 H 4 2 


Oxidation of acroleine. 


Crotonic 


C 4 H 6 2 


Croton-seed oil. 


Angelic . . 


C 5 H 8 2 


Angelica root. 


Pyroterebic 
Damaluric . 


C 6H 10 O 2 

C 7H 12 2 


Turpentine. 

Cow's urine (Sa^aXos, a calf). 


Campholic . 
Moringic 
Hypogeic . 
Physetoleic 
Oleic . . 


CioH 18 2 

^15^28^2 

£ C16H30O2 

C18H34O2 


Camphor. 

Moringa aptera (oil of ben). 
( Oil of ground nut. 
( Sperm-whale oil (Physeter macrocephalus). 

Most oils. 


Doeglic . . 
Brassic . . 


CigHggOs 


Doegling train oil. 
I Mustard seed. (fixed) oil. 
( Colza oil (Brassica oleifera). 


Erucic . . 


c C 22 H 42 2 



These acids are monobasic, their salts being formed by the substitution of 1 equi- 
valent of a metal for 1 of hydrogen. 

The following table exhibits the principal members of the allyle series, together 
with the corresponding members of the ethyle series : — 



Ethyle Series 




Allyle Series. 


Ethyle, 


C 2 H 5 . C 2 H 5 


Allyle, . . C 3 H 5 .C 3 H 5 


Ether, . 


(C 2 H 5 ) 2 


Allylic ether, . (C 3 H 5 ) 2 


Alcohol, 


C 2 H 5 .HO 


Allylic alcohol, C 3 H 5 .H0 


Iodide of ethyle, . 


C 2 H 5 I 


Iodide of aUyle, C 3 H 5 I 


Acetic ether, 


C 2 H 5 .C 2 H 3 2 


Acetate of allyle, C 3 H 5 .C 2 H 3 2 


Aldehyde, . 


C 2 H 4 


Allyle aldehyde, C 3 H 4 (acroleine) 


Acetic acid, . 


C 2 H 4 2 


Acrylic acid, . C 3 H 4 2 


Sulphide of ethyle, 


(C 2 H 5 ) 2 S 


Sulphide of allyle, (C 3 H 5 ) 2 S (oil of garlic) 


Triethylamine, 


N(C 2 H 5 ) 3 


Triallylamine, . N(C 3 H 5 ) 3 


Hydrate of tetrethy- 
lium, 


j N(C 2 H 5 ) 4 .HO 


Hydrate of te- ) N( c 8 H B > 4 .HO. 
trallylium, . ' 



568 STEARIC GLUCOSE — GLUCO-TARTAPJC ACID. 

It has been seen (p. 474) that glycerine, when distilled with biniodide 
of phosphorus, yields iodide of allyle (C 3 H 5 I). When this liqnid is treated 
with bromine it yields a crystallisable terbromide of allyle, C 3 H 5 Br 3 ; 
and if this be decomposed by acetate of silver, it furnishes the glyceride 
known as teracetine, thus — 

C 3 H 5 Br 3 + 3AgC 2 H,0, = C 3 H 5 .3C 2 H 3 2 + 3AgBr. 

Terbromide of allyle. Acetate of silver. Teracetine. 

When teracetine is submitted to the action of hydrate of baryta, glyce- 
rine is reproduced — 

2(C 3 EL3C 2 H 3 2 ) + 3(BaO.H 2 0) = 2C 3 H 8 3 + 3Ba2C 2 H 3 2 . 

Teracetine. Glycerine. Acetate of baryta. 

This affords an interesting example of the conversion of a monatomic 
radical, allyle (C 3 H 5 )', into a triatomic radical, glyceryle (CgE^)'". 

411. A very interesting chemical similarity has been pointed out 
between glycerine and mannite (C 6 H 14 6 ). It will be remembered that 
the former is a constant product of the alcoholic fermentation, and the 
latter, of a peculiar kind of fermentation (the viscous), to which saccha- 
rine liquids are subject. 

When mannite is heated, under pressure, with the acids of the acetic 
series, it forms compounds corresponding to those obtained when glycerine 
is so treated. Thus, with stearic acid — 

C 6 H 14 6 + 6C 18 H 3 A = PnAuPn + 7H 2 0. 

Mannite. Stearic acid. Mannite stearine. 

But it will be observed that 7 molecules of water are here eliminated 
instead of 3, as in the case of glycerine. The further examination of 
mannite explains this, for it is not that substance which is the true ana- 
logue of glycerine, but one which is obtained by heating mannite to 400° F. , 
when it loses a molecule of water, and is converted into mannitane — 

C 6 H 14 9 - H 2 = CM. 

Mannite. Mannitane. 

This mannitane or mannite-glycerine is a viscous substance, presenting 
a very strong resemblance to glycerine, so that it is not unlikely to have 
been mistaken for this substance iu examining some of the natural fats. 
The mannite-glycerides, or compounds formed by heating mannite with 
the fatty acids, are scarcely to be distinguished from stearine, palmitine, 
&c. They are saponified by alkalies in exactly the same manner. 

Cane-sugar and grape-sugar are capable of forming compounds corres- 
ponding to those obtained by the action of acids upon glycerine and 
mannite. Thus, if grape-sugar be heated to 250° F. for several hours in 
contact with stearic acid, it is converted into a fusible solid, insoluble in 
water, but soluble in alcohol and ether — 

C 6 H 12 6 + 2C 18 H 3 A = C 42 H 78 7 + 3H 2 0. 

^hydrous). Stearic acid. Stearic glucose. 

When grape-sugar is heated with tartaric acid, a similar reaction takes 
place, but the resulting product is a new acid — 

C H 12 O 6 + 2H 2 C 4 H 4 6 = H 2 C 14 H 1(i 15 + 3H 2 . 

Siyrb-ous) Tartaric acid. Gluco-tartaric acid. 

Cane-sugar behaves in a similar manner. 



NITROGLYCERINE. 569 

412. Nitroglycerine, or glonoine. — This violently explosive substance is 
very easily prepared by dissolving glycerine in a mixture of equal measures 
of the strongest nitric and sulphuric acids, previously cooled, and pouring 
the solution in a thin stream into a large volume of water, when the 
nitroglycerine is precipitated as a colourless heavy oil (sp. gr. 1*6). It is 
advisable to add the glycerine to the mixed acids in very small quantities 
at a time, and to cool the mixture in a vessel of water after each addition. 
When the nitroglycerine has subsided, the water may be poured off, and 
the oil shaken several times with water, so as to wash it thoroughly. 
The formation of nitroglycerine resembles that of gun-cotton (see p. 497), 
three atoms of hydrogen being removed from the glycerine by the 
oxidising action of the nitric acid, and three of nitric peroxide introduced 
in their place — 

C 3 H 8 3 + 3(HM) 3 ) = C 3 H 5 (N0. 2 ) 3 3 + 3H 2 0. 

Glycerine. Nitroglycerine. 

On a larger scale, a mixture of concentrated nitric acid (sp. gr. 1 "47 to 1 *49) with 
twice its weight of concentrated sulphuric acid is employed. The mixture is placed 
in stone jars containing about 7 lbs. each, which are immersed in running water, and 
about 1 lb. of glycerine (sp. gr. 1 "25) is gradually added, with frequent stirring, to the 
contents of each jar, care being taken that the temperature does not rise above 80° F. 
The mixture is allowed to settle for a quarter of an hour, and poured gradually into 
5 or 6 gallons of water. The oily nitroglycerine which falls to the bottom is well 
washed by stirring with water, a little alkali being added in the last washings. One 
per cent, of magnesia is sometimes added to the nitroglycerine in order to neutralise 
any acid arising from decomposition. 

This oil is very violent in its explosive effects. If a drop of nitro- 
glycerine be placed on an anvil and struck sharply, it explodes with a 
very loud report, even though not free from water ; and if a piece of 
paper moistened with a drop of it be struck, it' is blown into small frag- 
ments. On the ajDplication of a flame or of a red-hot iron to nitro- 
glycerine, it burns quietly ; and when heated over a lamp in the open air 
it explodes but feebly. In a closed vessel, however, it explodes at about 
360° F. with great violence. For blasting rocks, the nitroglycerine is 
poured into a hole in the rock, tamped by filling the hole with water, 
and exploded by the concussion caused by a detonating fuse (see p. 500). 
It has been stated to produce the same effect in blasting as ten times its 
weight of gunpowder, and much damage has occurred from the accidental 
explosion of nitroglycerine in course of transport. When nitroglycerine 
is kept, esjDecially if it be not thoroughly washed, it decomposes, with 
evolution of nitrous fumes and formation of crystals of oxalic acid ; and 
it may be readily imagined that, should the accumulation of gaseous pro- 
ducts of decomposition burst one of the bottles in a case of nitroglycerine, 
the concussion would explode the whole quantity. 

Nitroglycerine is particularly well fitted for blasting, because it will 
explode with equal violence whether moisture be present or not. On the 
other hand, it is very poisonous, and is said to affect the system seriously 
by absorption through the skin, and the gases resulting from its explo- 
sion are exceedingly acrid. Again, its fluidity prevents its use in any 
but downward bore-holes. To overcome these objections, and to diminish 
the danger of transport, several blasting compounds have been proposed, 
of which nitroglycerine is the basis. 

Dynamite is composed of a particularly porous siliceous earth, obtained 
from Oberlohe in Hanover, impregnated with about 70 per cent, of 
nitroglycpnnp. 



570 OILS AND FATS. 

Glyoxyline is a name given to gun-cotton pulp and saltpetre mixed with 
nitroglycerine. Litliofracteur is a more complex mixture containing 
about half its weight of nitroglycerine, together with nitrate of soda, 
sulphur, powdered coal, sawdust, and siliceous earth. Dualine is com- 
posed of nitroglycerine and sawdust. 

Nitroglycerine is readily soluble in ether and in wood-naphtha, but 
somewhat less so in alcohol ; it is reprecipitated by water from these last 
solutions. It becomes solid at 40° F., a circumstance which is unfavour- 
able to its use in mining operations, partly because it is then less sus- 
ceptible of explosion by the detonating fuze, and partly because serious 
accidents are said to have resulted from attempts to thaw the frozen 
nitroglycerine by heat, or to break it up with tools. It is remarkable 
that when made on the small scale, the nitroglycerine may generally 
be cooled down to 0° F. without becoming hard. This and other 
observations render it probable that some other substitution product is 
occasionally mixed with it. 

Oils and Fats. 

413. A very remarkable feature in the history of the fats is the close 
resemblance in chemical composition and properties which exists between 
them, whether derived from the vegetable or the animal kingdom. They 
all contain two or more neutral substances which furnish glycerine when 
saponified, together with some of the acids of the acetic series or of series 
closely allied to it. 

One of the most useful vegetable fatty matters is palm-oil, which is 
extracted by boiling water from the crushed fruit of the Elais guineensis, 
an African palm. It is a semi-solid fat, which becomes more solid when 
kept, since it then undergoes a species of fermentation, excited apparently 
by an albuminous substance contained in it, in consequence of which the 
palmitine (C^HggOg^is converted into glycerine and palmitic acid. The 
bleaching of palm-oil is effected by the action of a mixture of sulphuric 
or hydrochloric acid and bichromate of potash, which oxidises the yellow 
colouring matter. 

Cocoa-nut oil is also semi-solid, and is remarkable for the number of 
acids of the acetic series which it yields when saponified, viz., caproic, 
caprylic, rutic, lauric, myristic, and palmitic. 

These fats are chiefly used in the manufacture of soap and candles. 

Salad oil, or sweet oil (olive oil), is obtained by crushing olives, and an 
inferior kind which is used for soap is obtained by boiling the crushed 
fruit with water. When exposed to a temperature of about 32° F. a con- 
siderable portion of the oil solidifies ; this solid portion is generally called 
margarine (C 54 H 104 O 6 ) ; it is much less soluble in alcohol than stearine, 
though more so than palmitine. When saponified, margarine yields 
glycerine and margaric acid (C^H^O.J. This acid appears to be really 
composed of stearic and palmitic acids, into which it may be separated by 
repeated crystallisation from alcohol, when the palmitic acid is left in 
solution. The fusing-point of margaric acid is 140° F., that of stearic 
being 159°, and that of palmitic, 144°, but a mixture of 10 parts of pal- 
mitic with 1 part of stearic acid fuses at 140°. 

That portion of the olive oil which remains liquid below 32° con- 
sists of oleine (C 57 H 104 O H ), and forms nearly three-fourths of its weight. 
Oleine is not so easily saponified as the solid fats, and is resolved by 



SERIES OF DIBASIC FATTY ACIDS. 



571 



that process into glycerine and oleic acid (C 18 H 34 2 ), which differs from the 
other fatty acids by remaining liquid at temperatures above 40° F., and 
by absorbing oxygen from the air, when it is converted into a new acid 
which is not solidified by cold. 

Oleic acid is used in greasing wool for spinning, being much more 
easily removed by alkalies than olive oil which was formerly employed. 
Oleate of ammonia is sometimes employed as a mordant for the aniline 
dyes on cotton. 

The characteristic feature of oleic acid is its furnishing a solid crys- 
tallised acid when submitted to destructive distillation ; this acid is called 
sebacic acid, and is one of a series of dibasic acids, most of the other mem- 
bers of which may be obtained from oleic acid by the action of nitric acid. 

Dibasic Fatty Acid Series. 



Acid. 


Formula. 


Source. 


Oxalic 


C 2 H 2 4 


Oxalis acctosella (wood sorrel), &c. 


Malonic 


C 3 H 4 4 


Oxidation of malic acid. 


Succinic 


C 4 H 6 4 


Amber (succinum). 


Lipic 


C 5 H 8 4 


Oxidation of oleic acid (kivros, fat). 


Adipic 


C 6 !iio 4 


,, ,, (adepsfat), 


Pimelic 


C 7 H 12 4 


,, ,, (av/AsXjj, fat). 


Suberic 


Q&K\S*i 


Oxidation of stearic acid, and of cork (suber). 


Anckoic* . 


| 




Lepargylicf 


j C 9 H 16 4 


Oxidation of Chinese wax, and of cocoa-nutoil. 


Sebacic 


C10H18O4 


Distillation of oleic acid. 



The neutral salts of the acids of this series are formed by the displace- 
ment of two atoms of hydrogen by a metal. Thus, neutral succinate of 
potash has the composition C 4 (H 4 K 2 )0 4 . 

It is worthy of remark, that nine acids of the series, C n H 2n O a (from 
acetic to capric inclusive), are found among the products of the action of 
nitric acid upon oleic acid. 

It is well known that salad oil becomes rancid, and exhales a disagree- 
able odour after being kept for some time. This appears to be due to a 
fermentation similar to that noticed in the case of palm oil, originally 
started by the action of atmospheric oxygen upon albuminous matters 
present in the oil ; the neutral fatty matters are thus partly decomposed, 
as in saponification, their corresponding acids being liberated, and giving 
rise (in the case of the higher members of the acetic series, such as caproic 
and valerianic) to the disagreeble odour of rancid oil. By boiling the 
altered oil with water, and afterwards washing it with a weak solution of 
soda, it may be rendered sweet again. 

Almond oil, extracted by a process similar to that employed for olive oil, 
is also very similar in composition ; but colza oil, obtained from the seeds 
of the Brassica oleifera, contains only half its weight of oleine, and hence 
solidifies more readily than the others. 

Colza oil is largely used for burning in lamps, and undergoes a process 
of purification from the mucilaginous substances which are extracted with 

* From ayyui, to throttle,. from its suffocating vapours, 
t From XeVapyos, hewing white skin. 



572 FIXED OILS. 

it from the seed, and leave a bulky carbonaceous residue when subjected 
to destructive distillation in the wick of the lamp. To remove these, the 
oil is agitated with about 2 per cent, of oil of vitriol, which carbonises 
the mucilaginous substances, but leaves the oil untouched. When the 
carbonaceous flocks have subsided, the oil is drawn off, washed to remove 
the acid, and filtered through charcoal. 

Linseed oil, obtained from the seeds of the flax plant, is much richer in 
oleine than any of the foregoing, exhibiting no solidification till cooled 
to 15° or 20° F. below the freezing point. It exhibits, however, in a far 
higher degree, a tendency to become solid when exposed to the air, which 
has acquired for it the name of a drying oil, and renders it of the greatest 
use to painters, This solidification is attended with absorption of oxygen, 
which takes place so rapidly in the case of linseed oil, that spontaneous 
combustion has been known to take place in masses of rag or tow which 
have been smeared with it.* 

The tendency of linseed oil to solidify by exposure is much increased by 
heating it with about J^-th of litharge, or -^th. of binoxide of manganese ; 
these oxides are technically known as dryers, and oil so treated is called 
boiled linseed oil. The action of these metallic oxides is not well understood. 
The strong drying tendency of linseed oil is supposed to be due to a 
peculiarity in the oleine, which is said not to be ordinary oleine, but to 
furnish a different acid, linoleic acid, when saponified. When linseed oil 
is exposed for some time to a high temperature, it becomes viscous and 
treacly, and is used in this state for the preparation of printing-ink. If 
the viscous oil be boiled with dilute nitric acid, it is converted into artifi- 
cial caoutchouc, which is used in the manufacture of surgical instruments. 
This property appears to be connected with the drying qualities of the oil. 
Castor oil, obtained from the seeds of Ricinus communis, also yields a 
peculiar acid when saponified, termed ricinoleic (IT.C 18 H 33 3 ), containing 
one more atom of oxygen than oleic acid, which it much resembles. The 
destructive distillation of castor oil yields oenanthic acid (H.C 7 H 13 2 ), and 
oenanthole or oenanthic aldehyde (C 7 H 14 0), and by distilling it with caustic 
potash, caprylic alcohol (C 8 H J8 0) is obtained. As in the case of olive oil, 
the cold drawn castor oil, which is expressed from the seeds without the 
aid of heat, is much less liable to become rancid. Castor oil is much 
more soluble in alcohol than any other of the fixed oils. 

The various fish oils, such as seal and whale oil, also consist chiefly of 
oleine, and appear to owe their disagreeable odour to the presence of cer- 
tain volatile acids, such as valerianic. 

Cod-liver oil appears to contain, in addition to oleine and stearine, a- 
small quantity of acetine (C 9 H H ( .), which yields acetic acid and glycerine 
when saponified. Some of the constituents of bile have also been traced 
in it, as well as minute quantities of iodine and bromine. 

Butter contains about two-thirds of its weight of solid fat, which con- 
sists in great part of margarine (see p. 574), but contains also butine, which 
yields glycerine and butic acid (H„C. 20 H 39 O 2 ) when saponified. The liquid 
portion consists chiefly of oleine. Butter also contains small quantites of 
butyrine, caproine, and caprine, which yield, when saponified, glycerine 
and butyric (H.C 4 H 7 0. 2 ), caproic (H.C ti H n O.,), and capric (H.C 10 H 19 O 2 ) 
acids, distinguished for their disagreeable odour. 

* During the oxidation, a volatile compound is formed which resembles acroleine in 
smell, and colours unsized paper brown. It has been suggested that the brown colour 
and musty smell of old books may be due to the oxidation of the oil in the printing-ink. 



SPERMACETI — WAX. 573 

Fresh butter has very little odour, being free from these volatile acids, 
but if kept for some time, especially if the caseine of the milk has been 
imperfectly separated in its preparation, spontaneous resolution of these 
fats into glycerine and the volatile disagreeable acids takes place. By 
salting the butter this change is in great measure prevented. 

The fat of the sheep and ox (suet, or when melted, tallow), consists chiefly 
of stearine, whilst in that of the pig (lard) oleine predominates to about 
the same extent as in butter. Margarine (or palmitine 1) is also present in 
these fats. Bevzoated lard contains some gum benzoin, which prevents 
it from becoming rancid. 

Human fat contains chiefly oleine and margarine (or, if we do not admit 
the independent existence of the latter, palmitine and stearine). 

Sperm oil, which is expressed from the spermaceti found in the brain 
of the sperm whale, owes its peculiar odour to the presence of a fat which 
has been called phoc&nine, but which appears to be valerine, as it yields 
glycerine and valerianic acid (H.C 5 H 9 2 ) when saponified. 

The beautiful solid crystalline fat, known as spermaceti or cetine, differs 
widely from the ordinary fatty matters, for when saponified (which is not 
easily effected), it yields no glycerine, but in its stead another alcohol 
termed ethal (C 16 H 34 0), which is a white crystalline solid, capable of being 
distilled without decomposition. 

The soap prepared from spermaceti, when decomposed by an acid, yields 
palmitic acid (H.C 16 H 31 2 ), (formerly called etlialic acid), to which ethal is 
the corresponding alcohol. 

Palmitic acid and ethal are formed from spermaceti by the assimilation of the 
elements of water, just as stearic acid and gtycerine are formed from stearine — 

C 32 H 64 2 + H 2 = C 16 H 34 + H.C 16 H S1 2 . 

^cXf "ha,. Palmitic acid. 

Upon the compound radical theory, ethal would be represented as cetylic hydrate 
(C 16 H 33 )HO, and as the alcohol of the cetyle series, running parallel with the ethyle 
series. The following characteristic members of the series have been studied : — 



Cetyle Series. 


Ethyle Scries. 


Cetylene, C 16 H 32 
Cetylic ether, (C l6 H 33 ) 2 
Ethal, C 16 H 33 .HG 
Palmitic acid, C l6 H 31 2 .H 
Spermaceti, C 16 H 33 .C 16 H 31 2 


Ethylene, C 2 H 4 
Ether, (C 2 H 5 ) 2 
Alcohol, C 2 H..HO 
Acetic acid, C 2 H 3 2 .H 
Acetic ether, C 2 H 5 .C 2 EL 



Chinese wax, the produce of an insect of the cochineal tribe, is analogous 
in its chemical constitution to spermaceti. When saponified by fusion 
with caustic potash, it yields cerotine or cerylic alcohol (C 27 H 55 .HQ), 
corresponding to ethal, and cerotic acid (H.C 27 IL 3 2 ), corresponding to 
palmitic acid. Cerotic acid is also contained in ordinary bees' wax, from 
which it may be extracted by boiling alcohol, and crystallises as the solu- 
tion cools. It forms about two-thirds of the weight of the wax. Cerotic 
acid is found among the products of oxidation of paraffme by chromic 
acid. 

Bees' wax also contains about one-third of its weight of myricine 
(C 46 H 92 2 ), a substance analogous to spermaceti, which yields, when sapo- 
nified, palmitic acid and melissine (C 30 H 31 .HO), an alcohol corresponding 
to ethal. The colour, odour, and tenacity of bees' wax appear to be due 



574 



PREPARATION OF OXALIC ACID. 



to the presence of a greasy substance called ceroleine, which forms about 
^-th of the wax, and has not been fully examined. The tree wax of 
Japan is said to be pure palmitine. 

Wax is bleached for the manufacture of candles, by exposing it in thin 
strips or ribands to the oxidising action of the atmosphere, or by boiling 
it with nitrate of soda and sulphuric acid. Chlorine also bleaches it, but 
displaces a portion of the hydrogen in the wax, taking its place and causing 
the evolution of hydrochloric acid vapours when the wax is burnt. 

The following table includes the principal fatty bodies and their corresponding 
acids, with their fusing points : — 



Neutral 


Formula. 


Chief 


Fusing 


Fatty 


Formula. 


Fusing 


Fats. 


Source. 


Point. 


Acids. 


Point. 


Stearine* 


^.57 H 110^6 


Tallow- 


125° to 157° 


Stearic 




159° 


Palmitine 


C 5 iH 98 6 


Palm oil 


114° to 145° 


Palmitic 




144° 


Margarine 


C 54 H m 6 


Olive oil 


116° 


Margaric 


C 17 H 34 2 


140° 


Oleine 


C 5 7 H 10 />6 


,, 


Below 32° 


Oleic 


C 18 H 34 2 


40° 


Cetine 


C 32 H R4 2 


Spermaceti 


120° 


Palmitic 


C 16 H 32°2 


144° 


Myricine 


C 46 H 92 2 


Bees' wax 


162° 


» 







VEGETABLE ACIDS. 

414. Oxalic acid. — This very poisonous acid occurs pretty abundantly 
in the vegetable kingdom, being found in the leaves of the wood sorrel as 
binoxalate of potash (salt of sorrel, KHC. 2 4 .Aq.), in the stalks of 
rhubarb, in some sea- weeds, as oxalate of soda, and in lichens, some of 
which contain more than half their weight of oxalate of lime. Oxalate of 
lime has also been found in wood. In certain unhealthy conditions of the 
animal frame, oxalate of lime is produced, being either excreted in the 
urine, or forming a calculus (mulberry calculus) in the bladder. In such 
cases the oxalic acid appears to be formed in consequence of an imperfec- 
tion in that oxidising process by which the carbon and hydrogen of the 
various parts of the frame are finally converted into carbonic acid (CO.,) 
and water (H,0), the production of oxalic acid (C 2 H 2 4 ) representing the 
penultimate stage of that process. 

Guano contains a considerable quantity of oxalic acid in combination 
with ammonia and lime. 

With the exception of carbonic acid, no carbon compound is more com- 
monly met with than oxalic acid, as a product of the action of oxidising 
agents upon organic substances, especially upon those which do not con- 
tain nitrogen, such as sugar (C 12 H 22 O n ), starch (C 6 H 10 O 5 ), and woody 
fibre. 

Oxalic acid is largely employed in calico-printing, in cleansing leather 
and brass, as a solvent for Prussian blue in the preparation of blue ink, 
&c, and for taking iron-mould out of linen. It is manufactured on the 
large scale by oxidising sawdust with a mixture of hydrate of potash and 
hydrate of soda ; the latter would not produce oxalic acid without the 
hydrate of potash, and this alone would be too expensive. 1 mol. of 

* Stearine and palmitine are said to present three modifications with different fusing 
points. Some recent observations appear to indicate that the so-called palmitine of palm 
oil really contains stearine, oleine, and laurine 



PROPERTIES OF OXALIC ACID. 575 

hydrate of potash and 2 niols. of hydrate of soda are mixed in solution, 
which should have the sp. gr. 1*35, made into a thick paste with saw- 
dust, and heated upon iron plates for several hours ; hydrogen is evolved, 
from the decomposition of the water in the alkaline hydrates, the oxygen 
serving to convert the wood into oxalic acid, which forms more than one- 
fourth of the weight of the grey mass finally obtained. On treating this 
mass with cold water, a quantity of oxalate of soda is left undissolved ; 
this is boiled with hydrate of lime, when the oxalic acid is converted 
into the insoluble oxalate of lime, and hydrate of soda is dissolved ; 
the oxalate of lime is then decomposed by dilute sulphuric acid, when 
the sparingly soluble sulphate of lime is formed, and the solution yields 
crystals of oxalic acid (H 2 C 2 4 .2Aq.) on evaporation. The whole of the 
alkali originally employed is recovered by evaporating the liquors to dry- 
ness, calcining to destroy organic matter, and decomposing the alkaline 
carbonates with hydrate of lime. The sawdust yields about half its 
weight of crystallised oxalic acid. 

Before the introduction of this process, oxalic acid was sold at nearly 
twice its present cost, being then usually obtained by the action of nitric 
acid either upon molasses or upon starch-sugar* (p. 490) in leaden vessels, 
which were found to remain unattacked by the acid as long as any sugar 
remained unoxidised. 

For experiment on the small scale, oxalic acid may be prepared by gently heating 
100 grains of starch with 1% measured ounce of nitric acid (sp. gr. 1*38), when 
abundant fumes of nitrous acid (N 2 3 ) will indicate the deoxidation suffered by the 
nitric acid. When this has abated, the solution may be transferred to a dish, and 
slowly evaporated to about one-sixth of its bulk ; on cooling, a mass of beautiful 
four-sided prismatic crystals of oxalic acid will be obtained. 

The crystals of oxalic acid may be represented by the empirical formula 
C. 2 H 6 6 , but when they are heated to 212° F. they lose water, melting 
first, if the heat be suddenly applied,t but efflorescing without fusion if 
heated gradually. The dried or effloresced oxalic acid has the composi- 
tion C 2 H 2 4 , showing that 2 mols. of water of crystallisation have been ex- 
pelled, and that the crystals would be more correctly represented by 
C 2 H 2 4 . 2 Aq. On neutralising oxalic acid with potash and soda, salts are 
obtained which, when dried at 212° F., have the composition K 2 C 2 4 , and 
!N~a 2 C 2 4 , and if solutions of these salts be precipitated by nitrate of lead 
or of silver, the oxalates of lead (PbC 2 4 ) and of silver (Ag 2 C 2 4 ) are 
obtained. If the dried acid be heated to about 320° 17., it sublimes in 
crystals, but above that temperature it is decomposed into water, car- 
bonic acid, carbonic oxide, and some formic acid (see p. 557). When 
heated with dehydrating agents, such as sulphuric acid, it is also de- 
composed into carbonic acid and carbonic oxide (p. 86). 

Oxalic acid is rather sparingly soluble in cold water, requiring about 
nine times its weight ; hot water dissolves it more abundantly, and it is 
moderately soluble in alcohol. The aqueous solution is intensely acid, 
more nearly resembling the strong mineral acids than one of vegetable 
origin, and is exceedingly poisonous, a property which is the more 
dangerous on account of the resemblance of the crystallised oxalic acid to 
Epsom salts (sulphate of magnesia), from which, however, it may be 
readily distinguished by its sour taste and by the action of heat, which 

* Hence the common name, acid of sugar. 

t By suddenly heating the crystals with a lamp in a test-tube, much of the acid may be 
sublimed in Ions prismatic crystals. 



576 PREPARATION OF TARTARIC ACID. 

entirely dissipates the oxalic acid, but only expels water from Epsom 
salts. Fortunately, a considerable quantity of the acid is required to 
cause death, in ordinary cases 100 grains or more. The chemical anti- 
dote employed to counteract its effect is chalk suspended in water, the 
lime of the chalk combining with the acid to form the insoluble and 
harmless oxalate of lime (CaO.C 2 3 ). The insolubility of the oxalate of 
lime renders the oxalic acid one of the most delicate tests for lime, which 
may be detected, for example, in common water, by adding oxalic acid 
and a slight excess of ammonia, when a white cloud of oxalate of lime is 
produced. Conversely, of course, salts containing calcium (chloride of 
calcium, for instance) may be employed to detect oxalic acid, the precipi- 
tated oxalate of lime being distinguished from other similar precipitates 
by its insolubility in acetic acid. 

As might be expected from its composition (C 2 H 2 4 ), oxalic acid is 
easily converted into carbonic acid and water by oxidising agents; thus, 
if a hot solution of oxalic acid be poured upon powdered binoxide of 
manganese, violent effervescence takes place from the rapid evolution of 
carbonic acid. 

Binoxalate of potash (KHC 2 Q 4 .H 2 0) is sold under the names of salt of 
sorrel and essential salt of lemons, and is employed for the same purposes 
as oxalic acid. It is a sparingly soluble salt, requiring 40 parts of cold 
water to dissolve it, and has occasionally caused accidents by being mis- 
taken for cream of tartar (bitartrate of potash), from which it is readily 
distinguished by the action of heat, which chars the bitartrate, but not 
the binoxalate, an alkaline mass containing carbonate of potash being left 
in both cases. 

Qaadroxalate of potash (KH 3 2C 2 4 .2H 2 0) is also sometimes sold as 
salts of lemon ; it is even less soluble than the binoxalate. 

Oxalate of ammonia ((NH 4 ) 3 C.,0 4 .H 2 0), so much used in chemical 
analysis as a precipitant for lime, is obtained by mixing solution of 
oxalic acid with a slight excess of ammonia, and evaporating the solu- 
tion, from which the oxalate of ammonia crystallises, on cooling, in fine 
prismatic needles. 

The action of heat upon this salt has been described at p. 540. 

Oxalate of silver (Ag 2 C a 4 ) is obtained as a white precipitate when 
nitrate of silver is added to oxalate of ammonia. It is remarkable for 
being decomposed, with a slight explosion, when heated in the dry state, 
metallic silver being left, Ag 2 C 2 4 = Ag 2 + 2C0 2 . 

415. Tartaric acid. — The most important of the vegetable acids is tar-' 
taric acid (C 4 H 6 6 ) which occurs in many fruits, but more especially in 
the grape, the juice of which deposits it, during fermentation, in the form 
of bitartrate of potash, which is known in commerce as tartar or argol. 
This salt dissolves with difficulty in cold water, but may be dissolved in 
boiling water, from which it crystallises in prisms on cooling. When 
thus purified, it is known as cream of tartar, and has the composition 
KHC 4 H 4 O h , representing tartaric acid in which one atom of hydrogen has 
been replaced by potassium. The solution of this salt is acid to test- 
papers, and if it be neutralised with potash and evaporated, it yields 
crystals of a very soluble salt, having the composition K 2 C 4 H 4 O s . This 
is the neutral tartrate of potash, cream of tartar being a bitartrate. The 
crystallised tartaric acid is therefore regarded as H 2 C 4 H 4 0,.. 

In order to prepare tartaric acid, which is largely used in dyeing and 



TARTAR- EMETIC. 577 

calico-printing, the impure bitartrate of potash is boiled with water, and 
carbonate of lime (chalk) is added as long as it causes effervescence from 
the escape of carbonic acid ; the result of this change is the formation of 
tartrate of lime, which is insoluble, and tartrate of potash, which dissolves 
in the water — 

2(KHC 4 H 4 O e ) + 2(CaO.CO,) = 

Bitartrate of potash. Carbonate of lime. 

K 2 C 4 H 4 6 + CaC 4 H 4 6 + H 2 + 2C0 2 . 

Tartrate of potash. Tartrate of lime. 

Chloride of calcium is then added to the mixture, which converts the 
whole of the tartaric acid into the insoluble tartrate of lime — 

K 2 C 4 H 4 6 + CaCl 2 = 2KC1 + CaC 4 H 4 6 . 
The tartrate of lime is strained off, washed, and boiled with diluted sul- 
phuric acid, when sulphate of lime remains undissolved, and tartaric acid 
may be obtained in crystals by evaporating the filtered solution — 

CaC 4 H 4 6 + H 2 O.S0 3 - H 2 C 4 H 4 6 + CaO.S0 3 . 

Tartrate of lime. Tartaric acid. 

Large transparent prisms are thus obtained, which are soluble in about three- 
fourths of their weight of hot water. When kept, the solution, unless 
very strong, deposits a curious fungoid growth,* and acetic acid is found in 
it. When heated to about 340° F., the crystals fuse without loss of 
weight ; but on examining the fused mass, it is found to be no longer 
tartaric acid, but a mixture of two new acids. One of these, metatartaric 
acid, has the same formula as tartaric acid (H 2 C 4 H 4 6 ), but cannot be 
crystallised. Its salts are more soluble in water than the tartrates, and 
are converted into the latter when boiled with water. The other acid, 
isotartaric, is also uncrystallisable, but has the formula (HC 4 H 5 6 ). The 
isotartrate of potash (KC 4 H 5 6 ) has the same composition as the bitartrate 
(KHC 4 H 4 6 ), but is far more soluble. It is converted into that salt by 
boiling with water. 

At 374° F. tartaric acid loses water, and is converted into tartaric 
anhydride (C 8 H s O 10 ), which is a white insoluble substance, convertible 
into tartaric acid by prolonged contact with water. 

Tartar-emetic. — One of the commonest salts of tartaric acid is tartar- 
emetic, the double tartrate of antimony and potash, which is prepared by 
boiling antimony with sulphuric acid, driving off the excess of acid by 
heat, and digesting the residual teroxide of antimony with cream of tartar 
and a little water for some hours. The changes involved in the process 
are thus represented— 

Sb 2 4- 3(H 2 O.S0 3 ) = Sb 2 3 + 3H 2 + 3S0 2 
Sb 2 3 + 2KHC 4 H 4 6 = 2(K.SbO.C 4 H 4 6 ) + H 2 . 

Bitartrate of potash. Tartar-emetic. 

On boiling the mixture with water, and filtering, the cooled solution 
deposits octahedral crystals, of the formula 2(K.SbO.C 4 H 4 6 ).Aq. 

The water of crystallisation may be expelled at 212° F. ; and if the salt 
be heated to 400° F. it loses an additional molecule of water, and becomes 
K.Sb.C 4 H 2 6 , which is reconverted into tartar-emetic when dissolved in 
water. 

When a little hydrochloric acid is added to a solution of tartar-emetic, a precipi- 
tate of teroxide of antimony is formed, which dissolves easily in an excess of the acid. 

* This fungus has been found to contain 3 5 per cent, of nitrogen. 

2 O 



578 RACEMIC ACID. 

If kept for a length of time in solution, tartar-emetic is decomposed, octahedral 
crystals of teroxide of antimony being deposited, and the solution ceases to be preci- 
pitated by hydrochloric acid. The reaction to test-paper, which was slightly acid, 
is now slightly alkaline. 

Compounds perfectly analogous to tartar-emetic have been obtained, in 
which, the antimony is replaced by boron or by arsenic, and the potassium 
by silver, lead, or sodium. 

It will be observed that tartar-emetic presents an anomaly in its 
composition, for it might be expected to be KSb"'(C 4 H 4 6 ) 2 . The com- 
position of the tartar-emetic, dried at 400° F., might be reconciled with 
that of crystallised tartaric acid by representing it thus, C 4 (H 2 KSb /// )(\, 
that is, crystallised tartaric acid (C 4 H 6 6 ), in which one atom of hydrogen 
has been replaced by potassium, and three atoms by the triatomic anti- 
mony. 

The beautiful prismatic crystals known as Rochelle salt consist of a 
double tartrate of potash and soda (KNaC 4 H 4 6 , 4Aq.), prepared by 
neutralising cream of tartar with carbonate of soda. 

Tartaric acid has been obtained artificially by the action of nitric acid 
upon sugar of milk or gum, which supplies a link of connection between 
this acid and the members of the sugar group which accompany it in 
plants. 

Tartaric acid is easily convertible into succinic and malic acids, as might 
be anticipated from an inspection of their formulae — 

Tartaric acid, . . H 2 C 4 H 4 6 
Malie „ . . H 2 C 4 H 4 5 
•Succinic „ , . H 2 C 4 H 4 4 

When tartaric acid is heated with phosphorus and iodine in the presence 
of water (or, which amounts to the same thing, when it is heated with 
hydriodic acid), the acid is deoxidised, and malic and succinic acids are 
produced, thus— 

H 2 C 4 H 4 6 + 4HI = H 2 C 4 H 4 4 + I 4 + 2H 2 . 

Tartaric acid. Succinic acid. 

Tartaric and malic acids are frequently associated in fruits, and succinic 
acid is found among the products of fermentation of grape-juice. 

Succinic acid may be reconverted into tartaric acid by heating it with 
bromine and water, when it is converted into bibromosuccinic acid, 
H 2 C 4 (H 2 Br 2 )0 4 , which furnishes tartaric acid when decomposed with 
oxide of silver — 

H 2 C 4 (H 2 Br 2 )0 4 + Ag 2 + H 2 = H 2 C 4 H 4 6 + 2AgBr. 

Bibromosuccinic acid, Tartaric acid. 

When bromosuccinic acid, H 2 C 4 (H 3 Br)0 4 , is decomposed with oxide of 
silver, malic acid is formed — 

2H 2 C 4 (H 3 Br)0 4 + 3Ag 2 = 2Ag 2 C 4 H 4 5 + 2AgBr + H 2 . 

Bromosuccinic acid. Malate of silver. 

416. The tartaric acid found in grapes is accompanied, particularly in those of 
certain vintages and districts, by another acid called raeemic or paratartaric acid, 
which has the same composition as tartaric acid, but crystallises with a molecule 
of water (H 2 C 4 H 4 & .Aq.) The crystalline forms of these acids are the same, but 
the crystals of raeemic acid effloresce, from loss of water, when exposed to the air. 
Solution of raeemic acid is precipitated by the salts of lime, which do not precipitate 
tartaric acid unless it be previously neutralised. Moreover, although raeemic acid 



CITRIC ACID. 579 

forms, with potash and oxide of antimony, a salt corresponding in composition to 
tartar-emetic, this does not crystallise in octahedra, but in tufts of needles. 

There is a marked difference in the action of these two acids and their salts upon 
polarised light, for solutions of racemic acid and the racemates do not alter the plane 
of polarisation, whilst tartaric acid and the tartrates rotate it to the right. 

On carefully examining the crystalline forms of the tartrates, Pasteur observed 
that they generally presented an exception to that law of crystalline symmetry, which 
requires that a modification existing on any edge or face of a crystal should be 
repeated on all its other similar edges or faces, whereas in the crystals of the tartrates, 
certain of the edges are truncated without any corresponding modification of the 
others, and hemihedral forms are thus produced. Now, in general, it is found that if 
a substance forms hemihedral crystals, their hemihedrism is of such a character 
that they can be superposed upon each other, so that the united crystals shall exhibit 
a perfect symmetry upon each side of the plane of junction ; but the hemihedrism of 
the tartrates is such, that the crystals do not exhibit this symmetry when superposed 
upon each other, but when one is superposed upon the reflection of the other in a 
mirror, so that instead of presenting crystals which are, as usual, partly right and 
partly left-handed in their want of symmetry, the crystals of the tartrates are either 
all right-handed or all left-handed hemihedral crystals. 

When the action of solutions of these salts upon polarised light came to be 
examined, it was found that the right-handed crystals always rotated the plane of 
polarisation to the right, whilst the left-handed crystals produced a left-handed 
rotation. 

On separating the acids from these salts, they resembled each other precisely in 
all their chemical properties, but the acid from the right-handed salts furnished 
crystals which were hemihedral right-handedly, whilst that of the left-handed salts 
furnished left-handed hemihedral crystals ; moreover, the solution of the right- 
handed acid exerted a right-handed rotation upon the plane of polarisation, which 
was turned in the opposite direction by a solution of the left-handed acid. 

The former acid has been named dextro-tartaric acid, and is the usual form in 
which this acid is met with ; the other acid has been called lsevo-tartaric acid. In 
their chemical relations these acids are perfectly identical ; for the chemist they are 
both the same tartaric acid, equally well adapted for all the uses to which this acid 
is applied. 

Pasteur found that the double racemate of soda and ammonia furnished a crop of 
crystals containing both right-handed and left-handed hemihedral forms, and on 
separating them by hand, he found that the action of their solutions on polarised 
light corresponded with their hemihedrism, and on isolating the acids, the right- 
handed crystals furnished dextro-tartaric, the left-handed, lsevo -tartaric acid. 

This analysis of racemic acid was soon confirmed by its synthesis. On mixing 
concentrated solutions of equal parts of dextro-tartaric and laevo-tartaric acids, a 
considerable rise of temperature was observed, showing that combination had taken 
place, and the solution, which had no longer the power of rotating the plane of 
polarisation, furnished crystals of racemic acid. 

This remarkable instance of chemical combination between two acids which are, 
in their chemical properties, perfectly identical, to furnish a new acid differing from 
both, affords, by analogy, some support to the theory of the duplex constitution of 
many elementary and compound bodies. 

417. Citric acid (C 6 H 8 7 ) occurs in lemons, oranges, and most acidu- 
lous fruits. It is prepared from lemon-juice, which contains the acid in 
a free state, by neutralising it with chalk, when the citrate of lime 
(Ca 3 2C 6 H 5 7 ) is obtained, which is decomposed by dilute sulphuric acid ; 
the filtered solution, when evaporated, yields prismatic crystals of citric 
acid, which contain C 6 H 8 7 .Aq. They fuse at 212° F., and lose the 
water of crystallisation. From the formula of the citrate of lime, it will 
be seen that citric acid is tribasic, and should be written H 3 .C 6 H 5 7 ; 
hence, like ordinary phosphoric acid, it forms three series of salts. The 
citrates of soda, for example, have the composition — 

2(Na 3 C 6 HA)» 11A ^ 

^a 2 HC t H 5 7 .Aq. 

NaH 2 C ti HA.Aq. 



580 MALIC ACID. 

When citric acid is heated above 300° F., it is converted into aconitic 
acid (H 3 C 6 H 3 O fi ), another vegetable acid found in the different varieties 
of monkshood (aconitum). 

Citric acid is employed in dyeing and calico-printing, as well as in 
medicine. 

By fermentation in contact with yeast, the citrate of lime is converted into acetate 
end bntyrate of lime, with evolution of carbonic acid and hydrogen. The crude 
citrate of lime prepared in Sicily, and imported for the preparation of the acid, is 
found sometimes to undergo this change spontaneously, so that it has been recom- 
mended to neutralise the hot lemon-juice with carbonate of magnesia (which is 
abundant in Italy), when the tribasic citrate of magnesia is precipitated in minute 
crystals. By dissolving this precipitate in a fresh quantity of hot lemon-juice, and 
evaporating, the bibasic citrate of magnesia is obtained in crystals, which is recom- 
mended as the best form in which to import the acid into this country. 

418. Malic acid (H 2 C 4 H 4 5 ) is a crystalline acid found, as its name 
implies, in apples, and in many other fruits. It is present, together with 
oxalic acid, in rhubarb. Tobacco leaves also contain it in the form of 
bimalate of lime, CaH 2 2C 4 H 4 5 . 

In order to extract the malic acid from rhubarb stalks, it is converted into malate 
of lime, the solubility of which enables it to be separated from the insoluble citrate 
and tartrate of lime. The juice is squeezed out of the stalks by a press, nearly 
neutralised with slaked lime suspended in water, and chloride of calcium is added. 
The precipitate containing tartrate, citrate, phosphate, and oxalate of lime, is filtered 
off, and the liquid boiled down, when malate of lime (CaC 4 H 4 5 ) is separated. This 
is washed and added to hot nitric acid, diluted with ten measures of water, as long 
as it continues to be dissolved. On cooling, bimalate of lime is deposited, which is 
dissolved in water and decomposed by acetate of lead, when it gives a curious pre- 
cipitate of malate of lead (PbC 4 H 4 5 .3Aq.), which becomes crystalline on standing, 
and fuses in the liquid below the temperature of boiling water. By suspending the 
malate of lead in water, and decomposing it with hydrosulphuric acid, the lead is 
separated as sulphide, and a solution of malic acid is obtained, which gives deli- 
quescent prismatic crystals of the acid when evaporated to a syrup and set aside. 
Malic acid is decomposed by heat into two isomeric acids, the malmic and fumaric 
H 2 C 4 H 2 4 ; the latter is found in the plant known as fumitory (Fumaria officinalis). 

An excellent source of malic acid is the juice of the unripe berries of 
the mountain-ash, in which it is accompanied by a volatile oily acid of 
pungent aromatic odour ; this has been called parasorbic acid, and has 
the formula HC 6 H 7 2 . When fused with hydrate of potash, or boiled 
with a strong mineral acid, it suffers a remarkable conversion into a 
crystalline solid acid, having precisely the same composition, called sorbic 
acid. 

Under the influence of yeast, in the presence of water, malate of lime 
is converted into succinate and acetate of lime — 

3(H 2 C 4 H 4 5 ) = 2(H 2 C 4 H 4 4 ) + HC 2 H 3 2 + 2C0 2 + H 2 0. 

Malic acid. Succinic acid. Acetic acid. 

The amide of malic acid, nialamide, C 4 H 8 N 2 3 (malate of ammonia, 
(NH 4 ) 2 C 4 H 4 5 minus 2H 2 0), has attracted some attention, because it 
has the same composition as asparagine, a crystalline substance extracted 
from the juice of asparagus, marsh-mallow root, and some other plants ; 
but it is not identical with it, though asparagine, when acted on by 
nitrous acid, yields malic acid — 

C 4 H 8 ST 2 Os + N 2 3 = H 2 C 4 H 4 5 + H 2 + N 4 . 

Asparagine. Malic acid, 

Asparagine is really the amide of another acid, the aspartic, into the 



TANNING. 581 

ammonia-salt of which it becomes converted when heated for some time 
with water — 

C 4 H 8 N 2 3 + H 2 = (ira 4 )C 4 H 6 N0 4 . 

Asparagine. Aspartate of ammonia. 

419. Tannic acid, or tannin (C s7 H 22 17 ) the astringent principle of 
gall-nuts, from which it may he extracted by water, is characterised by 
two very useful properties, viz., by yielding a black precipitate with 
the salts of peroxide of iron, and by forming a tough insoluble compound 
with gelatine and gelatigenous membrane, the first being turned to account 
in the preparation of ink, and the second in that of leather. 

For the preparation of ink, three quarters of a pound of bruised nut- 
galls are digested in a gallon of cold water, and six ounces of green vitriol 
(sulphate of iron) are added, together with six ounces of gum, and a few 
drops of kreasote. The mixture is set aside for two or three weeks, being 
occasionally agitated, and the ink afterwards poured off from the undis- 
solved part of the nut-galls. 

Pure sulphate of iron (FeO.S0 3 ) and tannic acid might be mixed 
without change ; but when the mixture is exposed to the air, oxygen is 
absorbed, converting the protoxide of iron (FeO) into sesquioxide (Fe 2 3 ), 
which combines with the tannic acid to form a black precipitate of 
tannate of sesquioxide of iron, the exact composition of which is not 
known. The gum is added to render the liquid viscous, so as to prevent 
the subsidence of the black precipitate, and the kreasote prevents the ink 
from becoming mouldy. The brown colour of the ink in old manuscripts 
is due to the tannic acid having been partly removed by oxidation, leaving 
the brown peroxide of iron ; the stain of iron-mould, left by ink on linen 
after washing is due to the entire removal of the tannic acid by the alkali 
in the soap. 

Tanning. — When infusion of nut-galls is added to a solution of gelatine, 
the latter combines with the tannic acid, and a bulky precipitate is 
obtained. If a piece of skin, which has the same composition as gelatine, 
be placed in the infusion of nut-galls, it will absorb the whole of the 
tannic acid, and become converted into leather, which is much tougher 
than the raw skin, less permeable by water, and not liable to putrefaction. 

The first operation in the conversion of hides into leather, after they 
have been cleansed, consists in soaking them for three or four weeks in 
pits containing lime and water, which saponifies the fat, and loosens the 
hair. The same object is sometimes attained by allowing the hides to 
enter into putrefaction, when the resulting ammonia has the same effect as 
the lime. The loosened hair having been scraped off, the hides are soaked 
for twelve hours in water containing T ^Va$ n 0I> sulphuric acid, which 
removes adhering lime, and opens the pores of the skin, so as to fit it to 
receive the tanning liquid. 

The tanning material generally employed for hides is the infusion of 
oak-bark, which contains querci-tartnic acid, very similar in properties to 
tannic acid. The hides are soaked in an infusion of oak-bark for about 
six weeks, being passed in succession through several pits, in which the 
strength of the infusion is gradually increased. They are then packed in 
another pit with alternate layers of coarsely ground oak-bark ; the pit is 
filled with water, and left at rest for three months, when the hides are 
transferred to another pit, and treated in the same way ; but, of course, the 
position of the hides will be now reversed — that which was uppermost, 
and in contact with the weakest part of the tanning liquor, will now be 



582 TANNING. 

at the bottom. After the lapse of another three months the hide is gene- 
rally found to be tanned throughout, a section appearing of a uniform 
brown colour. It has now increased in weight from 30 to 40 per cent. 
The chemical part of the process being now completed, the leather is sub- 
jected to certain mechanical operations to give it the desired texture. For 
tanning the thinner kinds of leather, such as morocco, a substance called 
sumach is used, which consists of the ground shoots of the Rhus Coriaria, 
and contains a large proportion of tannic acid. 

Morocco leather is made from goat and sheep skins, which are denuded 
of hair by liming in the usual way, but the adhering lime is afterwards 
removed by means of a bath of sour bran, or flour. In order to tan the 
skin so prepared, it is sewn up in the form of a bag, which is filled with 
infusion of sumach, and allowed to soak in a vat of the infusion for some 
hours. A repetition of the process, with a stronger infusion, is necessary ; 
but the whole operation is completed in twenty- four hours. The skins 
are now washed and dyed, except in the case of red morocco, which is 
dyed before tanning, by steeping it first in alum or chloride of tin, as a 
mordant, and afterwards in infusion of cochineal. Black morocco is dyed 
with acetate of iron, which acts upon the tannic acid. The aniline dyes 
are now much employed for dyeing morocco. 

The kid of which gloves are made is not actually tanned, but submit- 
ted to an elaborate operation called taiving, the chief chemical features of 
which are the removal of the excess of lime,* and opening the pores of 
the skin by means of a sour mixture of bran and water, in which lactic 
acid is the agent ; and the subsequent impregnation of the porous skin 
with chloride of aluminum, by steeping it in a hot bath containing alum 
and common salt. The skins are afterwards softened by kneading in a 
mixture containing alum, flour, and the yolks of eggs. The putrefaction 
of the skin is as effectually prevented by the chloride of aluminum as by 
tanning. 

Wash leather and buckskin are not tanned, but shamoyed, which con- 
sists in sprinkling the prepared skins with oil, folding them up and 
stocking them under heavy wooden hammers for two or three hours. 
When the grease has been well forced in, they are exposed in a warm 
atmosphere, to promote the drying of the oil by absorption of oxygen 
(p. 572). These processes having been repeated the requisite number of 
times, the excess of oil is removed by a weak alkaline bath, and the skins 
are dried and rolled. The buff colour of wash-leather is imparted by a 
weak infusion of sumach. 

Parchment is made by stretching lamb or goat skin upon a frame, re- 
moving the hair by lime and scraping, as usual, and afterwards rubbing 
with pumice stone, until the proper thickness is acquired. 

Tannic acid, like many other proximate constituents of vegetables 
(see p. 472), when boiled with diluted sulphuric acid, yields grape-sugar, 
whilst a new acid may be obtained from the solution, which is known as 
gallic acidt — 

C 27 H, 2 17 + 5H 2 = 3(C 7 H,A) + C 8 H 14 7 . 

Tannic acid. Gallic acid. Grape-sugar. 

The addition of dilute sulphuric acid to the infusion of gall-nuts pro- 

* Polysulphides of sodium and calcium are sometimes employed for removing the hair. 

| It will be perceived that tannic acid is analogous in constitution to the gluco-tartaric 
acid mentioned at p. 568, which splits into grape-sugar and tartaric acid when boiled with 
dduted sulphuric acid, exactly as tannic acid splits into grape-sugar and gallic acid. 



GALLIC ACID. 583 

duces a precipitate composed of tannic and sulphuric acids, but this 
dissolves when boiled with excess of sulphuric acid, suffering the above 
change. 

420. Gallic acid (H s C 7 H 3 5 ) is also formed by the oxidation of 
tannic acid when exposed to the air, particularly in the presence of the 
matters associated with it in the gall-nut, which seem to act like the 
ferment in the quick vinegar process (p. 487). The method generally 
practised for obtaining gallic acid consists in exposing powdered nut-galls 
in a moist state to the action of the air for some weeks, in a warm place, 
when oxygen is absorbed, and carbonic acid evolved, the powder becoming 
covered with crystals of gallic acid (tannic acid does not crystallise). By 
boiling the mass with water, the gallic acid is extracted, and since, unlike 
tannic acid, it is very sparingly soluble in cold water, the greater portion 
crystallises out as the solution cools, in long silky needles, containing 
C 7 H 6 5 .Aq. 

In this process another acid is obtained in small quantity, which is 
insoluble in water, and has been called ellagic acid (HC 7 H 2 4 ) ; it 
possesses some interest, because it is found as a product of animal life in 
certain intestinal concretions or bczoars, occurring in the antelopes of 
Central Asia.* 

In most astringent substances a small quantity of gallic acid accom- 
panies the tannic. 

Gallic acid dissolves in oil of vitriol with a red colour, and when the 
solution is poured into water, a red-brown precipitate is obtained, called 
rufigallic acid (C 7 H 6 5 ), which is interesting from its property of dyeing 
calico red, if previously mordanted with alum. 

"When powdered nut-galls are heated in an iron pan surmounted with 
a cone of paper (see benzoic acid, p. 468) to about 420°, a quantity of 
crystals sublime into the cone, which are pyrogallic acid (C 6 H 6 3 ), or 
more properly, pyrogalline, for it is doubtful whether it is really an acid 
substance. 

Its formation from the tannic acid of the galls is explained by the 
equation — 

Cg-H^O^ (Tannic acid) + H 2 = 4(C 6 H 6 3 ) (Pyrogallic acid) + 3C0 2 . 

As its name implies, this acid may also be obtained by the action of heat 
upon gallic acid, which suffers a similar decomposition, t 

This substance is extensively prepared for use in photography, in which 
art its great tendency to absorb oxygen is called into play, rendering it 
capable of decomposing the salts of silver with immediate separation of 
the metal. 

The solution of pyrogallic acid soon becomes brown when exposed to 
the air, from absorption of oxygen, and if it be mixed with an alkali, it 
absorbs oxygen almost instantaneously, acquiring a very dark brown colour. 
This property renders pyrogallic acid very useful in the analysis of air 
and of other gases containing uncombined oxygen ; a portion of air con- 

* Ellagic acid is obtained as a crystalline precipitate by heating together, for some time, 
gallic and arsenic acids in solution ; 

4(C 7 H 6 5 ) + As 2 5 = 4(C 7 H 3 4 ) + As 2 3 + 6H 2 0. 
Gallic acid. Ellagic acid. 

+ By heating gallic acid under pressure with two or three parts of water to 410° F. for 
half-an-hour, and evaporating the solution, it is said that the theoretical quantity of pyro- 
gallic acid may be obtained. It may be decolorised with animal charcoal. 



584 COMPOSITION OF OPIUM. 

fined in a graduated tube over mercury (see fig. 83), is shaken with a 
strong solution of potash to absorb carbonic acid, and the diminution 
of volume having been noted, some solution of pyrogallic acid in four 
parts of water is introduced ; on shaking for a few seconds, the oxygen is 
entirely absorbed, when the volume of the nitrogen may be observed. 

The salts of tannic and gallic acids are not very well known. The 
latter appears to be a tribasic acid, so that its true formula would be 
H 3 C 7 H 3 O g the H 3 being replaceable by a metal. 

The acid character of pyrogallic acid is very feeble. 

The three acids are distinguished by their action upon the salts of iron. 
With pure protosulphate of iron (FeO.S0 3 ) neither tannic nor gallic acid 
gives any reaction, but pyrogallic acid gives a deep indigo blue solution ; 
whilst with persulphate (Fe 2 3 .3S03) or perchloride (Fe 2 Cl 6 ) of iron, the 
two former give a bluish-black precipitate, and pyrogallic acid gives a 
bright red solution. 

The presence of tannic acid in a vegetable infusion is easily recognised 
by the addition of perchloride of iron, but the hue which is produced is 
not the same in all astringent substances, because they contain different 
varieties of tannin. 

All these varieties, however, differ from tannic acid properly so called, 
in not furnishing pyrogallic acid when heated. 

The astringent principle of catechu (terra Japonica or cutch) and kino, 
which are used by tanners and dyers, is called mimotannic acid. 



VEGETABLE ALKALOIDS. 

421. In some plants the vegetable acids are combined with vegetable 
alkalies or alkaloids; thus in opium, the morphine is combined with 
meconic acid ; in cinchona bark, the quinine is combined with kinic acid. 
The methods adopted for the separation of these alkaloids from the acids 
and other substances associated with them are among the most important 
processes of practical chemistry. 

Extraction of the alkaloids from opium. — Opium is the concrete milky 
j uice which exudes on incising the unripe capsules of the Papaver somni- 
ferum, and is imported into this country from Persia, Turkey, Bengal, and 
Egypt, in the form of round masses or cakes enveloped in leaves • it has a 
dark colour, a soft waxy consistence, and a peculiar characteristic odour. 
Different samples vary much in composition, but the following result of 
an analysis of Smyrna opium will give an idea of the nature of this com- 
plex drug : — 



100 parts of Smyrna Opium contained- 



Gum, 

Caoutchouc, 

Resin, 

Oily matter, 

Meconic acid, 

Morphine, 

Narcotine, 



26-2 
6-0 
3-6 
2-2 
5-0 

10-8 
6-8 



Narceine, . . . .6*7 
Meconine, . . . . - 8 
Codeine, . . . .07 
Colouring and other organic ) , Q , 



matters 
Water. 



The medicinal value of opium appears to be due chiefly to the morphine 
(C 17 H 19 N0 3 ), which is present, for the most part, in the state of meconate 
of morphine ; in order to obtain it in the separate state, the opium is cut 
into slices and digested with water at a moderate heat for two or three 



EXTRACTION OF QUININE. 585 

hours ; the liquor is then strained and evaporated, a little chalk being 
added to neutralise the free acid. The concentrated solution, containing 
chiefly morphine and codeine, in combination with meconic and sulphuric 
acids, is mixed with solution of chloride of calcium, when the meconic 
acid is precipitated in combination with lime, carrying with it a great 
part of the colouring matter, and leaving in solution the hydrochlorates of 
morphine and codeine, which may be obtained in crystals by evaporation. 
The hydrochlorates are decolorised with animal charcoal and recrystallised. 
On adding ammonia to the solution containing these salts, the morphine 
only is precipitated, and may be purified by crystallisation from alcohol, 
which deposits it in white rectangular prisms, having the formula 
C 17 H 19 N0 3 .Aq. 

The solution from which the morphine has been precipitated still con- 
tains the hydrochlorate of codeine, and on decomposing it with potash, the 
codeine is precipitated in crystals, of the composition C 18 H 2l ]TO,.Aq. 

The mother-liquor from the hydrochlorates of morphine and codeine 
contains narcotine, narceine, meconine, thebaine, and papaverine, together 
with resin and colouring matter.* 

The leading features of morphine are its sparing solubility in cold water, 
its bitter taste and alkaline reaction, and narcotic poisonous properties. 
It is generally identified by its giving an inky blue colour with perchlo- 
ride of iron, and a golden yellow with nitric acid. 

The hydrochlorate of morphine (C 17 H 19 N0 3 .HC1), or muriate of mor- 
phia, is the chief form in which this alkaloid is used medicinally. 

Narcotine (C 2 . 2 H 23 N0 7 ) possesses some interest as having been the first 
base extracted from opium, whence it may be obtained by simply treating 
the drug with ether, in which the morphine is insoluble. The greater 
part of the narcotine is left in the residue after exhausting the opium 
with water, from which it is extracted by digestion with acetic acid • on 
neutralising the solution with ammonia, narcotine is precipitated. It is 
a weak base, and has no alkaline reaction. 

The meconic acid which exists in opium is a tribasic acid, having the 
formula H 3 C 7 H0 7 ; it is soluble in hot water, and crystallises on cooling 
in plates which contain three molecules of water of crystallisation. It 
gives a blood-red colour with solution of perchloride of iron. 

422. Extraction of quinine. — The cinchona or Peruvian bark, so highly 
prized for its medicinal qualities, is obtained chiefly from the districts 
around the Andes, and is imported in three varieties, of which the yellow 
cinchona is richest in quinine, the pale or grey bark in cinchonine, whilst 
the red bark contains both these bases in considerable quantity. The 
alkaloids are combined with Tcinic acid, and with a variety of tannin 
known as quinotannic acid. 

In order to extract them, the bruised bark is boiled with diluted 
hydrochloric acid, and the filtered solution, containing the hydrochlorates 
of quinine and cinchonine, is mixed with enough lime diffused through 
water to render it alkaline. The quinine and cinchonine, which are very 
sparingly soluble in cold water (requiring about 400 times their weight to 
dissolve them), are precipitated together with some of the colouring matter 
of the bark. 

The precipitate having been collected upon a linen strainer and strongly 
pressed, is treated with boiling alcohol, which dissolves both the alkaloids, 

* KwSeta, a poppy head; vapKri, torpor ; fivnwv, a poppy : 



586 KTNOKE — HYDROKINONE. 

leaving any excess of lime undissolved. A part of the alcohol is then 
recovered by distillation, and the solution containing the quinine and 
cinchonine is neutralised with sulphuric acid, so as to convert the alkaloids 
into sulphates, and is then decolorised with animal charcoal, and allowed 
to crystallise. Sulphate of quinine, being much less soluble in water than 
the sulphate of cinchonine, crystallises out first, leaving the latter in 
solution. 

The sulphate of quinine is dissolved in water and decomposed by am- 
monia, when the quinine is separated as a white powder, which may be 
dissolved in alcohol and crystallised. 

The liquid from which the sulphate of quinine has been deposited con- 
tains, in addition to the sulphate of cinchonine, another base having the 
same composition as quinine, but distinguished from it by the indisposi- 
tion of its sulphate to crystallise. This base is termed quinidine, and is 
produced from quinine under the influence of an excess of acid ; it is the 
most important constituent of the substance called quinoidine or amorphous 
quinine which is prepared for sale from the mother-liquors of the sulphate 
of quinine, and forms a cheap substitute for quinine in medicine. 

Quinine crystallises in small prisms, which have the composition 
C 20 H 24 N 2 O 2 .3Aq., and although sparingly soluble, even in boiling water, 
it has an extremely bitter taste, which is also possessed by its salts. 

Quinine is employed in medicine in the form of sulphate — 

(C 20 H 24 NA) 2 H 2 O.SO,7Aq.) 

which requires as much as 700 parts of cold water to dissolve it, but is 
readily dissolved in water acidulated with sulphuric acid, when it is con- 
verted into the acid sulphate of quinine (C 20 H 24 !Sr 2 O 2 .H 2 O.SO3). The 
solution is remarkable for its action upon light, for although it is perfectly 
colourless when held directly in front of the eye, if seen obliquely it 
appears to have, especially at the edge, a beautiful pale blue colour. This 
phenomenon, which is termed flnorescence f has been already referred to in 
the case of other substances (p. 473). 

Quinic or kinic acid. — By evaporating the infusion of cinchona bark 
from which the quinine and cinchonine have been separated by lime, 
crystals of kinate of lime are obtained, and by decomposing these with 
sulphuric acid, the kinic acid (HC 7 H n 6 ) passes into solution, whence it 
may be obtained in prismatic crystals. 

This acid is chiefly interesting on account of the peculiar properties of 
some of its derivatives. When distilled with sulphuric acid and binoxide 
of manganese, the oxygen evolved from the mixture converts the kinic 
acid into a new substance, which condenses in beautiful yellow needles 
called kinone or quinone — 

HC 7 H n 6 + 2 = C 6 H 4 2 + C0 2 + 4H 2 0. 

Kinic acid. Kinone. 

The same substance is obtained in a similar manner from one of the 
constituents of the coffee-berry (caffeic or caffeotannic acid). By dissolving 
kinone in water containing sulphurous acid gas, and evaporating the solu- 
tion, colourless crystals of hydrokinone are obtained — 

C 6 H 4 2 + 211,0 + S0 2 - C 6 H s 2 + H 2 0.1S0 3 . 

Kinone. Hydrokinone. 

When a solution of kinone is mixed with one of hydrokinone, beauti- 



COMPOSITION OF COFFEE. 



587 



ful green crystals are deposited, which are known as green hydrohinone 
(C 6 H 4 2 .C 6 H 6 0.,), and may also be obtained by the action of oxidising 
agents, such as ferric chloride, upon hydrokinone. When kinone is acted 
on with hydrochloric acid and chlorate of potash, it is converted into a 
yellow crystalline body, known as perchlorokinole or chloranile (C 6 C1 4 0. 2 ), 
which is also obtained in a similar way from aniline, salicine, and isatine. 
Potash dissolves it when heated, giving a purple solution. 

423. Tlieine or Caffeine — Tea— Coffee. — A very remarkable instance of 
the application of chemistry to explain the use of widely different articles 
of diet by different nations, with a view to the production of certain 
analogous effects upon the system, is seen in the case of coffee, tea, Para- 
guay tea, and the kola-nut (of Central Africa), which are very dissimilar 
in their sensible properties, and afford little or no gratification to the 
palate, owing what attractions they possess chiefly to the presence, in 
each, of one and the same active principle, or alkaloid, which has a 
special effect upon the animal economy. This alkaloid is known as 
caffeine or theine, and is associated in the three articles of diet men- 
tioned above, with various substances, which give rise to their diversity 
in flavour. 

- The raw coffee-berry presents, on the average, the following composi- 
tion : — 

100 parts of Raw Coffee contain — 

Woody fibre, 

Water, 

Fat, . . . 

Cane-sugar and gum, 

Legumine, or some allied substanc 

Caffeine, 

Caffeic acid, 

Mineral substances, 

When the raw berry is treated with hot water, the infusion, which con- 
tains the sugar and gum, the legumine, caffeine, and caffeic acid (C I4 H 16 7 ), 
has none of the peculiar fragrance which distinguishes the ordinary beve- 
rage, and is due to an aromatic volatile oily substance termed caffeone, 
formed during the roasting to which the berry is subjected before use. 
This volatile oil, which is present in very minute quantity, is produced 
from one of the soluble constituents of the berry (probably from the 
caffeic acid), for if the infusion of raw coffee be evaporated to dryness, 
the residue, when heated, acquires the characteristic odour of roasted 
coffee. 

The roasting is effected in ovens at a temperature rather below 400° F., 
when the berry swells greatly, and loses about Jth of its weight, becoming 
brittle, and easily ground to powder. It also becomes very much darker 
in colour, from the conversion of the greater part of its sugar into caramel 
(p. 494), which imparts the dark-brown colour to the infusion of coffee. 
If the roasting be carried too far, a very disagreeable flavour is imparted to 
the coffee by the action of heat upon the legumine and other nitrogenised 
substances contained in the berry. 

Prom 100 parts of the roasted coffee, boiling water extracts about 20 
parts, consisting of caffeine, caffeic acid, caramel, legumine, a little sus- 
pended fatty matter, fragrant volatile oil (caffeone), and salts of potash 
(especially the phosphate). The undissolved portion of the coffee contains, 





34-0 




12-0 




12-0 




15-5 


•e, . • . 


13-0 




1-5 




4-0 




7-0 



588 TEA — COCOA. 

beside the woody fibre, a considerable quantity of nitrogenised (and nutri- 
tious) matter, and hence the custom, in some countries, of taking this 
residue together with the infusion. 

In order to extract the caffeine from the infusion of coffee, it is mixed 
with solution of tribasic acetate of lead, to precipitate the caffeic acid and 
a part of the colouring matter. Through the filtered solution, sulphuretted 
hydrogen is passed to remove the lead as sulphide, and the liquid filtered 
from this is evaporated to a small bulk, when the caffeine crystallises out 
in white silky needles, which have a bitter taste, and the composition 
C 8 H 10 N" 4 O 2 .H 2 O. Its basic properties are very feeble. 

The constituents of the leaves of the tea-plant (Thea Sinensis) exhibit a 
general similarity to those of the coffee-berry. In the fresh leaf we find, 
in addition to the woody fibre, a large quantity of a substance containing 
nitrogen, similar to legumine, an astringent acid similar to tannic acid, a 
small quantity of caffeine, and some mineral constituents. 

The aroma of tea does not belong to the fresh leaf, but is produced, like 
that of coffee, during the process of drying by heat, which developes a 
small quantity of a peculiar volatile oil, having powerful stimulating 
properties. The freshly-dried leaf is comparatively so rich in this oil 
that it is not deemed advisable to use it until it has been kept for some 
time. 

Green and black tea are the produce of the same plant, the difference 
being caused by the mode of preparation. For green tea the leaves are 
dried over a fire as soon as they are gathered, whilst those intended for 
black tea are allowed to remain exposed to the air in heaps for several 
hours, and are then rolled with the hands and partially dried over a fire, 
these processes being repeated three or four times to develope the desired 
flavour. The black colour appears to be due to the action of the air upon 
the tannin present in the leaf. 

Boiling water extracts about 30 parts of soluble matter from 100 of 
black tea, and 36 from 100 of green tea. The principal constituents of 
the infusion of tea are tannin, aromatic oil, of which green tea contains 
about 0*8 and black tea 0'6 per cent., and caffeine, the proportion of 
which, in the dried leaf, varies from 2*2 to 4*1 per cent., being present in 
larger quantity in green tea. 

The spent leaves contain the greater part of the legumine, and a con- 
siderable quantity of caffeine, which may be extracted by boiling them 
with water, and treating the decoction as above recommended in the case 
of coffee. 

If tea be boiled with water, the solution precipitated with tribasic- 
acetate of lead, the filtered liquid evaporated to dryness, and the residue 
cautiously heated, the caffeine sublimes in beautiful crystals. 

Cocoa and chocolate are prepared from the cacao-nut, which is the 
seed of Theobroma Cacao, and is characterised by the presence of more 
than half of its weight {minus the busk) of a fatty substance known as 
cacao-butter, and consisting of oleine and stearine, which does not become 
rancid like the natural fats generally. The cacao-nut also contains a 
large quantity of starch, a nitrogenised substance resembling gluten, to- 
gether with gum, sugar, and theobromine, a feeble base very similar to 
caffeine, but having the composition C 7 H s N 4 2 . 

The seeds are allowed to ferment in heaps for a short time, which im- 
proves their flavour, dried in the sun and roasted like coffee, which de- 
velopes the peculiar aroma of cocoa. The roasted beans having been 



TOBACCO. 589 

crushed and winnowed to separate the husks, are ground in warm mills, 
in which the fatty matter melts and unites with the ground beans to a 
paste, which is mixed with sugar and pressed into moulds. In the pre- 
paration of chocolate, vanilla and spices are also added. 

From the composition of cocoa and chocolate it is seen that when con- 
sumed, as is usual, in the form of a paste, they would prove far more 
nutritious than mere infusions of tea and coffee. 

Caffeine appears to be a methylated derivative from theobromine, for when it is 
boiled with potash, methylamine is evolved, and by acting with iodide of methyle 
(CH 3 I) upon a silver-compound obtained from theobromine, C 7 (H 7 Ag)]Sr 4 2 , the 
silver and methyle change places, yielding Agl and caffeine, C 7 H 7 (CH 3 )N 4 2 or 
methyle-theobromine. 

424. The vegetable alkali strychnine (C 21 H 22 N 2 2 ), only too well known 
for its activity as a poison, is contained in crow-fig or Nux-vomica, the 
seed of the poison-nut tree of the East Indies, and in several other plants 
of the same family. The strychnine appears to be combined, in the nux- 
vomica, with lactic acid, and is accompanied by a second alkaloid, brucine 
(C 23 H 26 N 2 4 ). In order to extract it, the bruised seeds are boiled with 
water acidulated with hydrochloric acid, the solution is strained, and ren- 
dered alkaline by adding hydrate of lime, which displaces the strychnine 
and brucine from their combination with the acid, and separates them in 
the form of a precipitate. When this is boiled with alcohol, the excess of 
lime remains undissolved, whilst the strychnine and brucine are carried 
into solution ; and since the former is less soluble in alcohol than the 
latter, it is deposited, before the brucine, on evaporating the liquid, in the 
form either of octahedral or prismatic crystals, which have an intensely 
bitter taste. This remarkable bitterness is one of the most prominent 
characters of strychnine ; for although 7000 parts of water are required to 
dissolve one part of this alkaloid, the solution possesses an intolerably 
bitter flavour, even when further diluted with 100 times its weight of 
water. Chloroform and benzole both dissolve strychnine with great ease ; 
and since these liquids refuse to mix with water, they are often employed 
to extract the rjoison from a large bulk of aqueous liquid by agitating it 
with a small quantity of one of them, which is then separated from the 
water and evaporated, in order to obtain the strychnine in the solid form. 
Very minute quantities may then be identified by moistening with strong 
sulphuric acid, and adding a minute quantity of chromate of potash, when 
the chromic acid acts upon the strychnine, giving rise to products of oxida- 
tion, which pervade the liquid in the form of beautiful purple streaks. 

Curarine, C 10 H 15 ISr, is a crystalline alkaloid which has been extracted 
from the icoorari or curara poison employed by the American Indians for 
poisoning arrows. It dissolves easily in water and alcohol, but not in 
ether. Strong sulphuric acid gives it a fine blue colour. 

425. Tobacco owes its active character chiefly to the presence of a vege- 
table alkali which is not found in any other plant than the Nicotiana 
tabacum, from the leaf of which the various forms of tobacco are manu- 
factured. This alkali, nicotine (C 10 H 14 N 2 ), is distinguished from most 
others by the absence of oxygen, and by its liquid condition at the ordi- 
nary temperature. 

In order to extract the nicotine from tobacco, the leaves are boiled with 
water, which dissolves the alkaloid, in combination with malic and citric 
acids. The liquid, having been strained, is evaporated to a syrup and 
mixed with alcohol, when it separates into two layers, of which the 



590 TOBACCO. 

upper contains the salts of nicotine dissolved in alcohol, the lower aqueous 
layer retaining the greater part of the extraneous vegetable matters. The 
alcoholic layer having been drawn off, is next shaken with potash, to 
combine with the acids, and with ether to dissolve the nicotine then set 
free. On decanting the ethereal solution of nicotine which rises to the 
surface, and evaporating the ether, the nicotine is left in the form of an 
oily liquid, which is colourless when perfectly pure, but soon acquires a 
dark brown colour when exposed to the air. It is very readily distin- 
guished by its very pungent, irritating odour, recalling that of tobacco, 
and which is very perceptible at the common temperature, although the 
boiling point of nicotine is so high as 480° F. Water, alcohol, and ether 
dissolve nicotine with facility. The poisonous action of this alkaloid upon 
animals is very powerful, death almost immediately following its adminis- 
tration. The Virginian tobacco contains more nicotine than other varieties, 
the alkaloid amounting to nearly 7 per cent, of the weight of the leaf 
dried at 212° F., whilst the Maryland and Havannah varieties contain 
only 2 or 3 per cent, of nicotine. Tobacco is remarkable for the very 
large amount of ash which it leaves when burnt, amounting to about one- 
fifth of the weight of the dried leaf, and containing about one-third of car- 
bonate of potash, resulting from the decomposition of the malate, citrate, 
and nitrate of potash during the combustion. The presence of this latter 
salt in large quantity (3 or 4 parts in 100 of the dried leaf) distinguishes 
tobacco from most other plants, and accounts for the peculiar smouldering 
combustion of the dried leaves. 

Cigars are made directly from the tobacco leaves, which are only mois- 
tened with a weak solution of salt in order to impart the requisite sup- 
pleness ; but snuff, after being thus moistened, is subjected, in large 
heaps, to a fermentation extending over eighteen or twenty months, which 
results in its becoming alkaline from the development of carbonate of 
ammonia (by the putrefaction of the vegetable albumen in the leaf) and 
of a minute quantity of free nicotine, which imparts the peculiar pungency 
to this form of tobacco. The aroma of the snuff appears to be due to 
the production of a peculiar volatile oil during the fermentation. The 
proportion of nicotine in snuff is only about two per cent., being one-third 
of that found in the unferrnented tobacco ; and a great part of this exists 
in the snuff in combination with acetic acid, which is also a result of the 
fermentation. It is also not improbable that a little acetic ether is pro- 
duced, and perhaps some other acids and ethers of the acetic series (e.g., 
butyric and valerianic), of which extremely minute quantities would give 
rise to great differences in the aroma of the snuff. 



COLOURING MATTER OF PLANTS. 591 



VEGETABLE COLOURING MATTERS. 

426. Notwithstanding the great variety and "beauty of the tints exhi- 
bited by plants, comparatively few yield colouring matters which are 
sufficiently permanent to be employed in the arts ; the greater number of 
them fading rapidly as soon as the plant dies, since they are unable to 
resist the decomposing action of light, oxygen, and moisture, unless sup- 
ported by the vital influence in the plant, some of them even fading during 
the life of the plant, as may be seen in some varieties of the rose, which 
are only fully coloured in those parts which have been partly obscured. 

The green colouring matter of plants has been termed chlorophyll,* and 
is a resinous substance containing carbon, hydrogen, nitrogen, and oxygen, 
which has never yet been obtained in so pure a condition that its composi- 
tion could be accurately determined, since it -cannot be crystallised or 
distilled, aud is therefore not amenable to the usual methods by which 
organic substances are obtained in a pure state. 

When green leaves are boiled with alcohol, the latter acquires a fine 
green colour, and, when evaporated, deposits the chlorophyll. When the 
alcoholic solution of chlorophyll is boiled with alcoholic solution of 
potashj and hydrochloric acid afterwards added, a yellow precipitate (phyl- 
loxanthine) is obtained, and a fine blue colouring matter (phyllocyanine) 
remains in solution. The blue matter contains nitrogen, and both are 
insoluble in water. The autumnal colour of leaves may possibly be due 
to the disappearance of the phyllocyanine. On immersing green leaves 
in chlorine they assume an autumnal tint. 

The blue colouring matter contained in many flowers, such as the violet, 
has been named cyanine. Acids change its blue colour to red, and hence 
the blue colour is exhibited only by flowers the juice of which is neutral, 
whilst red flowers yield an acid juice. The colouring matter of grapes 
and of red wine appears to be identical with cyanine. 

Two yellow colouring matters have been extracted from flowers, and 
have been named xanthine and xantheine, the latter being soluble in water. 

Saffron is a yellow colouring matter obtained from the flowers of the 
Crocus sativus, which are themselves of a blue, colour, but have yellow 
anthers. When these are dried and pressed into cakes, they form the 
saffron of commerce, which is characterised by its very remarkable and 
somewhat agreeable odour. The yellow colouring matter is readily dis- 
solved by water and alcohol, and has been found to be a glucoside, which 
yields, when treated with sulphuric acid, beside glucose, crocine, C 16 H 18 6 , 
and an essential oil having the formula C 10 H 14 O. 

Safflower consists of the petals of the Carthamus tinctorius, a plant 
cultivated in Egypt. It furnishes a red colouring matter called cartha- 
mine (C 14 H 16 7 ), which is used in dyeing, although it fades easily when 
exposed to light. It exhibits the characters of an acid, being dissolved 
by alkalies and reprecipitated by acids, a circumstance which is taken 
advantage of when extracting it from the safflower. 

The orange-yellow colouring matter known as annatto is extracted from 
the seeds of the Bixa Orellana, a native of the West Indies. The colouring 
principle has been called bixine, and is dissolved by alkalies, but precipi- 
tated again by acids. Annatto is used for colouring butter and cheese. 

A valuable yellow colour is obtained from the weld, or Reseda luteola, 
, * XXo)po9, green ; <f>v\\ov, a leaf. 



592 ARTIFICIAL ALIZARINE. 

by boiling the dried leaves with water. This colouring matter is termed 
luteoline (C. 20 H 14 O 8 ), and may be sublimed in yellow needles. 

The woods of various trees, when boiled with water, furnish colouring 
matters of considerable importance ; thus, the wood of Morns tinctoria, 
or fustic, a West Indian tree, yields a crystalline yellow colour called 
moritannic acid (C 18 H 16 O 10 ), 

Logwood is the wood of the Hcematoxylon GampecManum, which grows 
at Campeachy, in the Bay of Honduras. Its most important constituent 
is a yellow colouring matter called hcematoxyline, which may be obtained 
in needle-like crystals having the composition (C 16 H 14 6 ,Aq.) It becomes 
intensely red in contact with alkalies and oxygen, from the formation of 
haematein (C 16 H 12 6 ). Chromate of potash gives an intense black colour 
with infusion of logwood, which has been used as an ink, but is not per- 
manent. 

Brazil wood, which is employed in the preparation of red ink, contains 
a colouring matter somewhat resembling that of logwood. 

The well-known Turkey red colour is obtained from madder, the root 
of the Rubia tinctorum, imported from the south of France and the 
Levant. This root does not contain any red colouring matter during the 
life of the plant, but a yellow substance {rubian, C. 28 H 34 15 ), from the decom- 
position of which the madder red is obtained. There are several methods 
in use for obtaining the red colour from madder. If the root be steeped 
in water for some time, so that some of the nitrogenised constituents begin 
to undergo decomposition, a peculiar fermentation is excited in the rubian, 
resulting in its decomposition into several new bodies, the chief of which 
are a red crystalline colouring matter, alizarine (C 14 H 8 4 ), and an un- 
crystallisable sugar. The alizarine may be dissolved out either by water 
or alcohol, and maybe obtained in beautiful plates having a golden lustre. 

If the madder root be boiled with water, the rubian is dissolved, ard 
when this solution is boiled with dilute sulphuric acid, the rubian under- 
goes a decomposition similar to that mentioned above, and the alizarine, 
being insoluble in the dilute acid, is precipitated. 

Madder which has been treated with hot sulphuric acid, so as to decom- 
pose the rubian, is used in print-works under the name of garancine, and 
yields a red solution containing alizarine when boiled with water. 

Artificial alizarine. — The disco very of a process for the artificial pro- 
duction of the colouring matter of madder from anthracene, one of the 
constituents of coal-tar, is one of the most important services which 
chemistry has, of late years, rendered to the useful arts, and affords an 
excellent illustration of the practical importance of the minute study of 
the constitution of organic substances. When alizarine, C 14 H 8 4 , was 
heated with powdered zinc, it was found to be converted into anthra- 
cene, C 14 H 10 , a substance obtained among the last products of the dis- 
tillation of coal-tar, for which no useful application had hitherto been 
discovered.* It somewhat resembles naphthaline in properties, but may 
be distinguished from it by its sparing solubility in alcohol. When treated 
with nitric acid, or with sulphuric acid and binoxide of manganese, 
it yields a crystalline compound known as oxanthracene, C 14 H 8 0. 2 , which 
bears the same relation to anthracene as quinone (p. 586) (C c H 4 2 ) bears 
to benzole (C 6 H 6 ), and has therefore been called anthraquinone. When 
acted upon by bromine, this is converted into dibromantliraquinone, 
C 14 H.Br 2 O a . By heating this to about 350° F. with caustic potash, 
* C H H 8 4 + H 2 + Zn 5 = 5ZnO + C 14 H 10 . 



COLOURING MATTERS PREPARED FROM LICHENS. 593 

C 14 H 6 Br 2 2 + 4KHO = C 14 H 6 K J! 4 (potassic alizarate) + 2KBr + 2H 2 0. 
Alizarine is precipitated by decomposing the potassic alizarate with hydro- 
chloric acid, C 14 H 6 K 2 4 + 2HC1 = C 14 H 8 4 (alizarine) + 2KC1. A cheaper 
process for the artificial formation of alizarine consists in heating the 
anthraquinone with oil of vitriol, so as to convert it into disulphanthro- 
quinonic acid, which is afterwards converted into potassic a]izarate by 
being heated with caustic potash ; C 14 H 8 2 , (anthraquinone) + 2(H 2 .S0 2 .0 5 .) 
(oil of vitriol) = C 14 H 8 .(S0 2 ) 2 .0 4 (disulphoanthraquinonic acid) + 2H 2 0. 
When this acid is heated to about 350° F. with caustic potash, 
C 14 H 8 (S0 2 ) 2 .0 4 + 6KHO = C 14 H 6 K 2 4 (potassic alizarate) + 2(K s O.SO„) 
+ 4H 2 0. 

The scientific interest of this production of alizarine from anthracene is 
enhanced by the circumstance that anthracene has itself been produced 
by synthesis ; for carbon and hydrogen combine, at a high temperature, 
to produce acetylene (C 2 H 2 ), three molecules of which coalesce at a high 
temperature to form benzole (C 6 H 6 ), and by acting upon two molecules of 
benzole with one molecule of ethylene, anthracene has been produced, 
2C 6 H 6 + C 2 H 4 = C 14 H 10 + H 6 . 

Turmeric is the root of an East Indian plant, the Curcuma longa ; its 
colouring matter, called curcumine, is nearly insoluble in water, but dis- 
solves in alcohol. Its yellow colour is changed to brown by alkalies, 
which leads to its use in the laboratory as a test of alkalinity. 

427. Litmus, archil, and cudbear are brilliant, though not very per- 
manent purple and violet colours, prepared from various lichens, such as 
Roccella tinctoria (litmus), and Lecanora tartarea (cudbear*). 

Archil and cudbear owe their colour chiefly to the presence of orceine 
(CyHWOy), which does not exist ready formed in any of the lichens, but 
is developed during the preparation which they undergo. 

If either of the above lichens be digested for some hours with lime and 
water, and the filtered solution be neutralised with hydrochloric acid, a 
white gelatinous precipitate is obtained, which dissolves in hot alcohol, 
and is deposited in crystals on cooling. This substance may consist, ac- 
cording to the particular lichen employed, of one or more acids, the chief 
of which have been named erythric (C 20 H 22 O 10 -), evernic (C 1? H 16 7 ), and 
lecanoric (C 8 H 8 4 ) acids. These acids are remarkable for the facility**with 
which they furnish compound ethers when boiled with alcohol. 

When either of these acids is boiled with an excess of lime or baryta, it 
is decomposed, and if the excess of base be removed by carbonic acid, the 
filtered liquid evaporated to a syrup, and extracted with boiling alcohol, 
the latter deposits prismatic crystals of or cine (C 7 H 8 2 .Aq.) The forma- 
tion of this body will be understood from the following equations — 



a H 22 O 10 + 2(CaO.H 2 0) = 

Erythric acid. 


= 2(CaO.C0 2 ) + 2C 7 H 8 2 

Orcine. 


+ C 4 H 10 O 4 

Erythrite. 


C 17 H 16 7 + CaO.H 2 = 

Evernic acid. 


= CaO.C0 2 + C 9 H 10 O 4 + 

Evernesic 
fifirl. 


C 7 H s O a . 

Orcine. 



Pure orcine is a colourless substance, but when exposed to the joint action 
of ammonia and air, it is converted into a beautiful red colouring matter, 
orceine — 

C 7 H 8 2 + NH 3 + 3 = C 7 H 7 N0 3 + 2H 2 0. 

Orcine. Orceine. 

* Said to have been named after Cuthbert, a manufacturer of the dye. 

2 p 



594 BLUE AND WHITE INDIGO. 

Orceine does not crystallise, and dissolves to a slight extent only in water, 
but readily in alcohol and in alkaline liquids, yielding, in the latter 
case, a beautiful purple solution, which becomes red when mixed with 
acids, and deposits red flakes of orceine. 

The chemistry of the processes by which archil and cudbear are pre- 
pared will now be easily understood. The powdered lichen is mixed with 
urine (to furnish ammonia) and lime, and exposed to the air for some 
weeks, when the lime decomposes the erythric and other acids, with forma- 
tion of orcine, which then passes into orceine under the influence of the 
ammonia and atmospheric oxygen. 

The preparation of litmus from the Roccella tinctoria is similar to that 
just described, but a mixture of carbonate of ammonia and carbonate of 
potash is employed instead of the urine and lime. The chemical change 
which takes place, although similar in principle, is not precisely identical 
with the foregoing, for the principal colouring matter developed appears 
to be a red substance called azolitmine (C 9 H 10 NO 5 ), which differs from 
orceine by its insolubility in alcohol. It dissolves in alkaline solutions 
with a beautiful blue colour, which is immediately reddened by acids, a 
property frequently turned to account by the chemist for detecting the 
acid reaction. Litmus occurs in commerce in small cakes, which are 
made up with chalk. 

Erytlirite (C 4 H 10 O 4 ) is a crystalline substance extracted from various 
lichens and fungi, which forms combinations with the fatty acids similar 
to those formed by glycerine. It is sometimes represented as a tetratomic 
alcohol (p. 554), (C 4 H,) iv H 4 .0 4 . 

428. Indigo blue (C g H 5 ]S!"0) is prepared from various species of Indigo- 
fera, grown in China, India, and America. The plants are covered with 
cold water and allowed to ferment ; as soon as a blue scum appears upon 
the surface, a little lime is added and the mixture stirred briskly for some 
time, when the indigo is deposited in a pulverulent form ; it is collected 
on calico strainers, pressed and cut up into cakes. 

The theory of the process is not yet clearly explained ; it is certain 
that the indigo blue does not pre-exist in the plant, but is a product of 
the fermentation. Recent observations have shown that the indigo plants 
probably contain a substance called indican (C 2s H 3 N0 18 ), which stands 
in a similar relation to indigo blue to that in which rubian stands to 
alizarine (in the case of madder) ; it is soluble in water, and when heated 
with an acid, splits up into indigo blue, indigo red, and a peculiar un- 
crystallisable sugar. The indigo red may be extracted from commercial 
indigo by boiling with alcohol, in which the indigo blue is insoluble. 
Since indigo blue is insoluble in all ordinary solvents, it is necessary, in 
order to use it for dyeing, to reduce it to the condition of white indigo, 
which is soluble in alkalies. 

If 2 parts of protosulphate of iron (copperas) be dissolved in 200 parts 
of water, and well shaken in a stoppered bottle with- 1 part of powdered 
indigo and 3 of slaked lime, the indigo will disappear, and on. allowing 
the precipitate to subside, a yellow fluid will be obtained, which becomes 
blue at the surface as soon as it is exposed to air. If this solution be 
mixed with hydrochloric acid, out of contact with air, a flocculent precipi- 
tate of white indigo is obtained. The composition of this substance is 
C 8 H 6 NO, and it is formed from blue indigo (C 8 H 5 NO) by the addition of 
an atom of hydrogen derived from water, the oxygen of which has com- 



DYEING AND CALICO-PKINTTNG. 595 

bined with the protoxide of iron ; one portion of the lime combines with 
the sulphuric acid of the sulphate of iron, whilst another serves to dis- 
solve the white indigo, which is soluble in alkaline liquids — 

FeO.S0 3 + CaO.H 2 = FeO.H 2 + CaO.S0 3 . 
2(FeO.H 2 0) + H 2 + 2CgH 5 ^0 = Fe. 2 3 .2H 2 + 2C 8 H 6 M) . 

Blue indigo. White indigo. 

The solution of white indigo prepared by this process is employed for 
dyeing linen and cotton, which are immersed in the vat, and then exposed 
to the air, the oxygen of which removes an atom of hydrogen from the 
white indigo, and the blue indigo thus formed is precipitated upon the 
fibre. 

Other reducing agents are sometimes substituted for the protosulphate 
of iron. Even decaying vegetable matter effects the conversion of blue 
into white indigo in an alkaline liquid. Thus, for some purposes, the vat 
is prepared by fermenting a mixture of indigo, madder, carbonate of potash, 
and lime, when the hydrogen extricated in the fermentation of the vege- 
table matter converts the blue into white indigo, which is then dissolved 
by the potash liberated from the carbonate by the lime, 

When cloth is dyed with indigo (Saxony blue) the colour is dissolved 
by means of sulphuric acid. Fuming sulphuric acid dissolves indigo blue 
very readily, but oil of vitriol does not act quite so well. The solution 
thus obtained is commonly called sul/phindigotic acid, but it really con- 
tains two acids, the sulphindylic (HC 8 H 4 !N"O.S0 3 ) and liyposulphindigotic. 
The blue solution becomes colourless when shaken with powdered zinc, 
and resumes its blue colour when shaken with air. 

On heating indigo, it evolves purple vapours, which condense in pris- 
matic crystals of a coppery lustre, consisting of pure indigotine or indigo 
blue (C 6 H 5 KO), which may be obtained in larger quantity by digesting 
indigo with grape-sugar, caustic soda, and weak alcohol, when a solution 
of white indigo is obtained which deposits the crystallised indigotine on 
exposure to air. 

429. Animal colouring matters. — From the animal kingdom only two 
colouring matters of any great importance are derived, viz., cochineal and 
lac, both which are obtained from insects of the coccus tribe. The colour- 
ing matter of cochineal is known as carmine, and may be extracted 
from the insects by water or alcohol. It has acid properties, and has 
been named carminic acid (C 14 H U 8 ). Carmine-lake is a combination of 
this acid with alumina, precipitated when a solution of alum and an 
alkaline carbonate are added to one of cochineal. 



Dyeing and Calico-Printtng. 

430. The object of the dyer being to fix certain colouring matters 
permanently in the fabric, his processes would be expected to vary 
with the nature of the latter and of the colour to be applied to it. In 
order that uniformity of colour and its perfect penetration into the fibre 
maybe attained, it is evident that the colouring matter must always be 
employed in a state of solution ; and it must be rendered fast, or not 
removable by washing, by assuming an insoluble condition in the fibre. 
The simplest form of dyeing is that in which the fibre itself forms an in- 



596 USE OF MORDANTS. 

soluble compound with, the colouring matter. Thus, if a skein of silk be 
immersed in a solution of indigo in sulphuric acid, it removes the whole 
of the colouring matter from the liquid, and may then be washed with water 
without losing colour; but if the same experiment be tried with cotton, 
the indigo will not be withdrawn from the solution, and when the cotton 
has been well squeezed and rinsed with water, it will become white again. 
It may be stated generally, that the animal fabrics (silk and wool) will 
absorb and retain colouring matters with much greater facility than 
vegetable fabrics (cotton and linen). In the absence of so powerful an 
attraction between the fibre and the colouring matter, it is usual to impreg- 
nate the fabric with a mordant or substance having an attraction for the 
colour, and capable of forming an insoluble combination with it, so as to 
retain it permanently attached to the fabric. Thus, if a piece of cotton 
be boiled in a solution of acetate of alumina, the alumina will be precipi- 
tated in the fibre ; and if the cotton be then soaked in solution of 
cochineal or of logwood, the red colouring matter will form an insoluble 
compound (or lake) with the alumina, and the cotton will be dyed of a 
fast red colour. 

Another method of fixing the colour in the fabric consists in impregnat- 
ing the latter with two or more liquids in succession, by the admixture 
of which the colour may be produced in an insoluble state. If a piece of 
any stuff be soaked in solution of perchloride of iron, and afterwards in 
ferrocyanide of potassium, the Prussian blue which is precipitated in the 
fibre will impart a fast blue tint. 

An indispensable preliminary step to the dyeing of any fabric is the 
removal of all natural grease or colouring matter, which is effected by 
processes varying with the nature of the fibre, and is preceded, in the 
cases of cotton and woollen materials which are to receive a pattern, by 
certain operations of shaving and singeing, for removing the short hairs 
from the surface. 

From linen and cotton, the extraneous matters (such as grease and resin) 
are generally removed by weak solutions of carbonate of potash or of 
soda, and the fabrics are afterwards bleached by treatment with chloride 
of lime (p. 151). But since the fibres of silk and wool are much more 
easily injured by alkalies ,and by chlorine, greater care is requisite in 
cleansing them. Silk is boiled with a solution of white soap to remove 
the gum, as it is technically termed ; but the natural grease is extracted 
from wool by soaking at a moderate temperature in a weak bath either of 
soap or of ammoniacal (putrefied) urine. Both silk and wool are bleached 
by sulphurous acid (p. 200). 

Among the red dyes the most important are madder, Brazil wood, 
cochineal, lac, and the colours derived from aniline. 

In dyeing red with madder or Brazil wood, the linen, cotton, or wool 
is first mordanted by boiling in a solution containing alum and bitartrate 
of potash, when it combines with a part of the alumina, and on plunging 
the stuff into a hot infusion of madder, the colouring matter forms an in- 
soluble combination with that earth. 

To dye Turkey-red, the stuff is also mordanted with alum, but has pre- 
viously to undergo several processes of treatment with oil and with galls, 
the necessity of which is satisfactorily established in practice, though it is 
not easy to explain their action. The colour is finally brightened by 
boiling the stuff with chloride of tin. 

Woollen cloth is dyed scarlet with lac or cochineal, having been first 



PATTERNS IN CALICO-PRINTING. 597 

mordanted by boiling in a mixture of perchloride of tin and Mtartrate of 
potash. 

The aniline colours (see p. 451) are employed for dyeing silk and wool, 
either without any mordant or with the help of albumen. 

Blues are generally dyed with indigo (p. 595), or with Prussian blue > in 
the latter case the stuff is steeped successively in solutions of a salt of 
peroxide of iron and of ferrocyanide of potassium. Aniline blue is also 
much employed for silk and woollen fabrics. 

The principal yellow dyes are weld, quercitron, fustic, annatto, chrys- 
aniline, and chromate of lead. For the four first colouring matters 
aluminous mordants are generally applied. Chromate of lead is produced 
in the fibre of the stuff, which is soaked for that purpose, first in a solu- 
tion of acetate or nitrate of lead, and then in chromate of potash. 

Carbazotic acid (p. 4:56) is also sometimes employed as a yellow dye. 

In dyeing blacks and browns, the stuffs are .steeped first in a bath con- 
taining some form of tannin (p. 581), such as infusion of galls, sumach, or 
catechu, and afterwards in a solution of a salt of iron, different shades 
being produced by the addition of indigo, of sulphate of copper, &c. 

431. The art of calico-printing differs from that of dyeing, in that the 
colour is required to be applied only to certain parts of the fabric, so as 
to produce a pattern or design either of one or of several colours. 

A common method of printing a coloured pattern upon a white ground 
consists in impressing the pattern by passing the stuff under a roller, to 
which an appropriate mordant thickened with British gum (p. 481) is ap- 
plied. The stuff is then dunged, i.e., drawn through a mixture of cow- 
dung and water, which appears to act by removing the excess of the 
mordant, and afterwards immersed in the hot dye-bath, when the colour 
becomes permanently fixed to the mordanted device, but may be removed 
from the rest of the stuff by washing. 

If the pattern be printed with a solution of acetate of iron, and the 
stuff immersed in a madder-bath, a lilac or black pattern will be obtained 
according to the strength of the mordant employed. By using acetate of 
alumina as a mordant, the madder-bath would give a red pattern. 

A process which is the reverse of this is sometimes employed, the 
pattern being impressed with a resist, that is, a' substance which will pre- 
vent the stuff from taking the colour in those parts which have been 
impregnated with it. Foi example, if a pattern be printed with thickened 
tartaric or citric acid, and the stuff be then passed through an aluminous 
mordant, the pattern will refuse to take up the alumina, and subse- 
quently, the colour from the dye-bath. Or a pattern may be printed with 
nitrate of copper, and the stuff passed through a bath of reduced indigo 
(p. 594), when the nitrate of copper will oxidise the indigo, and by con- 
verting it into the blue insoluble form, will prevent it from sinking into 
the fibre of those parts to which the nitrate has been applied, whilst else- 
where, the fibre, having become impregnated with the white indigo, 
acquires a fast blue tint when exposed to the air. 

Sometimes the stuff is uniformly dyed, and the colour discharged in 
order to form the pattern. A white pattern is produced upon a red 
(madder) or blue (indigo) ground by printing with a thickened acid dis- 
charge, and passing the stuff through a weak bath of chloride of lime, 
which removes the colour from those parts only which were impregnated 
with the acid (p, 151). By adding nitrate of lead to the acid discharge, 



593 DIFFICULTIES OF ANIMAL CHEMISTRY. 

and finally passing the stuff through solution of chromate of potash, a 
yellow pattern (chromate of lead) may be obtained upon the madder red 
ground. 

By applying nitric acid as a discharge, a yellow pattern may be obtained 
upon an indigo ground (p. 131). 

Very brilliant designs are produced by mordanting the stuff in a solu- 
tion of stannate of potash or soda (p. 383), and immersing it in dilute sul- 
phuric acid, which precipitates the stannic acid in the fibre. When the 
thickened colouring matters are printed on in patterns, and exposed to the 
action of steam, an insoluble compound is formed between the colour and 
the stannic acid, which usually exhibits a very hue and permanent 
colour. 

It is evident that by combining the principles of which an outline has 
just been given, the most varied parti-coloured patterns may be printed. 



ANIMAL CHEMISTKY. 

432. Our acquaintance with the chemistry of the substances composing 
the bodies of animals is still very limited, although the attention of mauy 
accomplished investigators has been directed to this branch of the science. 
The reasons for this are to be found, firstly, in the susceptibility to change 
exhibited by animal substances when removed from the influence of life ; 
and secondly, in the absence, in such substances, of certain physical pro- 
perties by which we might be enabled to separate them from other bodies 
with which they are associated, and to verify their purity when obtained 
in a separate state. Two of the most important of these properties are 
volatility and the tendency to crystallise. When a substance can suffer 
distillation without change, it will be remembered that its boiling point 
affords a criterion of its purity ; or if it be capable of crystallising, this 
may be taken advantage of in separating it from other substances which 
crystallise more or less easily than itself, and its purity may be ascertained 
from the absence of crystals of any other form than that belonging to the 
substance. But the greater number of the components of animal frames can 
neither be crystallised nor distilled, so that many of the analyses which 
have been made of such substances differ widely from each other, because 
the analyst could never be sure of the perfect purity of his material ; and 
even when concordant results have been obtained as to the percentage 
composition of the substance, the atomic formula deduced from it has been- 
of so singular and exceptional a character as to cast very strong suspicion 
upon the purity of the substance. 

Accordingly, the chemical formulae of a great many animal substances 
are perfectly unintelligible, conveying not the least information as to the 
position in which the compound stands with respect to other substances, 
or the changes which it might undergo under given circumstances. 

It has been shown in the previous chapters of this work that we are 
gradually learning to class all compound bodies under a few typical forms, 
so that the chemical properties of any substance may in many cases be 
predicted from its composition as indicating the type to which it belongs. 
Take, for example, the class of alcohols (C„H, M + 2 0), or of volatile acids 
(C n H 2n 2 ), or of ammonias (XY 3 ), and it will be seen that even those 
formulae which are apparently the most complex, are perfectly intelligible 



.' MILK. 599 

when referred to their proper type (p. 534). But the extraordinary for- 
mulas, for example, deduced from the ultimate analysis of 
Albumen, C 108 H X69 K. 27 O 34 S and 

Caseine, C 144 H 228 N 36 45 S 

cannot be referred to any known type, and refuse to be classed with other 
substances, even if a type were invented expressly for them. 

Animal chemistry is for the above reasons in a very backward condition, 
as compared with vegetable and mineral chemistry, though an observation 
of the progress of research affords us the consolation, that a steady advance 
is being made towards a generalisation of the facts which have been dis- 
covered, especially by analogical reasoning from those two other depart- 
ments of the science. 

Milk. — The chemistry of milk is well adapted to introduce the study 
of animal chemistry, because that liquid contains representatives of all the 
substances which make up the animal frame ; and it is on this account 
that it occupies so high a position among articles of food. 

Although, to the unaided eye, milk appears to be a perfectly homo- 
geneous fluid, the microscope reveals the presence of innumerable globules 
floating in a transparent liquid, which is thus rendered opaque. If milk 
be very violently agitated for several hours, masses of an oily fat (butter, 
p. 572) are separated from it, and leave the liquid transparent. This fat 
was originally distributed throughout the milk in minute globules enclosed 
in very thin membranes, which were torn by the violent agitation, and 
the fatty globules then cohered into larger masses. 

For the preparation of butter, it is usual to allow the milk to stand for 
some hours, when a layer of cream collects upon the surface, the propor- 
tion of which is very variable, but is generally about y^th of the volume 
of the milk. The skimmed milk retains about half of the fatty matter. 
This cream contains about 5 per cent, (by weight) of fat, 3 per cent, of 
caseine, and water. When the cream is churned, the enclosing membranes 
of the fat globules are broken, and the fat unites into a semi-solid mass 
of butter, from which the butter-milk containing the caseine may be 
separated. If this be not done effectually, the caseine which is left in 
the butter, being a nitrogenised substance, will soon begin to decompose, 
and will induce a decomposition in the butter, (p. 572), resulting in the 
elimination of certain volatile acids, which impart to it a rancid and offen- 
sive taste and odour. To prevent this, salt is generally added to butter 
which has been less carefully prepared, in order to preserve the caseine 
from decomposition. Butter-milk contains about one-fourth of the fatty 
matter of the milk. 

Pure butter is essentially a mixture of margarine and oleine with 
smaller quantities of other fats, such as butyrine, caprine, and caproine 
(p. 572). 

Fresh milk is slightly alkaline to test-papers, but after a short time it 
acquires an acid reaction ; and if it be then heated, it coagulates from the 
separation of the caseine. This spontaneous acidification of milk is caused 
by the fermentation of the sugar of milk, under the influence of the caseine, 
which results in the production of lactic acid, according to the equation — 
CiX 4 12 = 4HC 3 H 5 3 . 

Sugar of milk. Lactic acid. 

The caseine, being insoluble in the acid fluid, separates in the form of 
curd. This development of lactic acid is spoken of as the lactic fermen- 



600 CHEESE. 

tation, and may be excited not only in milk sugar, but in other substances 
analogous to it. This is taken advantage of in the preparation of lactic 
acid, for which purpose 8 parts of cane-sugar are dissolved in 50 parts of 
water, and 1 part of poor cheese with 3 parts of chalk are added to the 
mixture, which is then allowed to remain for some weeks at about 80° F. 
The lactic acid formed from the cane-sugar (C 12 H 22 O n ), under the influence 
of the changing caseine in the cheese, combines with the lime of the chalk, 
disengaging the carbonic acid, and forming crystals of lactate of lime 
(Ca2C i H 5 3 ). This is dissolved in boiling water, recrystallised in order 
to purify it, and digested with one-third of its weight of sulphuric acid, 
which converts the lime into sulphate, liberating the lactic acid ; by add- 
ing alcohol, the whole of the sulphate of lime is precipitated, and the 
lactic acid is dissolved by the alcohol, which leaves it on evaporation as a 
colourless, syrupy, very acid liquid, which may be distilled, though with 
some loss from decomposition, if heated out of contact with air. 

By heating lactic acid to about 270° F. for a considerable length of 
time, a molecule of water is expelled, and the lactic anhydride (C 6 H 10 O 5 ) 
is left as a brownish glassy substance, which is reconverted into the 
acid by boiling with water. At a temperature of 500° F. lactic acid 
undergoes a destructive distillation, the most interesting product of 
which is a transparent crystalline substance called lactide (G.H 4 2 ) dif- 
fering from lactic acid by the elements of water, which it resumes when 
dissolved in that liquid, being converted into lactic acid (C 3 H 6 3 ). When 
lactic acid is heated with hydriodic acid in a sealed tube, it is converted 
into propionic acid — 

HC 3 H 5 3 (Lactic acid) + 2HI = HC 3 H 5 2 (Propionic acid) + H^O + I 2 . 

Lactic acid is an important constituent of the animal body, being found 
in the juice of muscular flesh, in the gastric juice, &c. 

If milk be maintained at a temperature of about 90° F., the fermenta- 
tion induced by the caseine results in the production of alcohol and car- 
bonic acid, for although milk-sugar is not fermented like ordinary sugar 
by contact with yeast, it appears, under the influence of the changing 
caseine at a favourable temperature, to be converted first into grape-sugar 
(p. 485), and afterwards into alcohol and carbonic acid. The Tartars pre- 
pare an intoxicating liquid, which they call kowniss, by the fermentation 
of milk. 

When an acid is added to milk, the caseine is separated in the form of 
curd, in consequence of the neutralisation of the soda which retains it 
dissolved in fresh milk, and this curd carries with it, mechanically, the 
fat globules of the milk, leaving a clear yellow ivliey. 

In the preparation of cheese, the milk is coagulated by means of rennet, 
which is prepared from the lining membrane of a calf's stomach. This is 
left in contact with the warm milk for some hours, until the coagulation is 
completed. This action of rennet upon milk has not yet received any satis- 
factory explanation. The curd is collected and pressed into cheeses, which 
are allowed to ripen in a cool place, where they are occasionally sprinkled 
with salt. The peculiar flavour which the cheese thus acquires is due to 
the decomposition of the fatty matter under the influence of the caseine, 
giving rise to the production of certain volatile acids, such as butyric, 
valerianic, and caproic, which have very powerful and characteristic odours. 
If this ripening be allowed to proceed very far, ammonia is developed by 
the putrefaction of the caseine, and in some cases the ethers of the above- 



SU&AR OF MILK. 601 

mentioned acids are produced, at the expense probably 03' a little sugar of 
milk left in the cheese, conferring the peculiar aroma perceptible in some 
varieties of it. 

The different kinds of cheese are dependent upon the kind of milk 
used in their preparation, the richer cheeses being, of course, obtained 
from milk containing a large proportion of cream ; such cheese fuses at a 
moderate heat, and makes good toasted cheese, whilst that wliich contains 
little butter never fuses completely, but dries and shrivels like leather. 

Double Gloucester and Stilton are made from a mixture of new milk 
and cream. Chedder cheese is made from new milk alone. Cheshire 
and American cheeses, from milk robbed of about one-eighth of its cream. 
Dutch cheese and the Skim Dick of the midland counties, from skimmed 
milk. 

Caseins. — The pure curd of milk is known as caseine and consists 
essentially of carbon, hydrogen, nitrogen, oxygen, and a small proportion 
(one per cent.) of sulphur. The simplest expression of the result of the 
analysis of caseine, in formula, would be C 144 H 2 . 28 N 3 ,.0 45 S, but the anoma- 
lous complexity of this formula conveys a suspicion that the composition of 
pure caseine has yet to be fixed. By whatever process it has been purified, 
hitherto it has always been found to retain saline matters. The com- 
plexity of its composition accounts for its liability to undergo putrefactive 
decomposition. 

Coagulated caseine is characterised by the facility with which it is dis- 
solved by alkaline solutions, such as carbonate of soda, yielding a liquid 
upon the surface of which, when boiled, an insoluble pellicle forms, exactly 
similar to that which forms upon the surface of boiled milk. Coagulated 
caseine may also be dissolved by acetic or oxalic acid, but the addition of 
sulphuric or hydrochloric acid reprecipitates it, these acids apparently 
forming insoluble compounds with caseine. 

If skimmed milk be carefully evaporated to dryness, and the fat extracted 
from the residue by ether, the caseine is left in the soluble form mixed 
with milk-sugar, and is capable of dissolving in water or in weak alcohol. 

Caseine appears to possess the properties of a weak acid, since it 
combines both with the alkalies and alkaline earths, and is even said to 
be capable of partially neutralising the former. / A mixture of cheese am" 
slaked lime is sometimes used as a cement for earthenware, the caseine 
combining with the lime to form a hard insoluble mass. The curd of 
milk, washed and dried, is used by calico-printers, under the name of 
Jadarine, for fixing colours. If it be dissolved in weak ammonia, mixed 
with one of the aniline dyes, printed on calico, and steamed, the am- 
monia is expelled, and the colour is left behind as an insoluble compound 
with the caseine. 

Caseine, or a substance so closely resembling it as to be easily con- 
founded with it, is found in peas, beans, and most leguminous seeds. If 
dried peas be crushed and digested for some time in tepid water, a turbid 
liquid is obtained, holding starch in suspension. If this be allowed to 
settle, the clear liquid is an impure aqueous solution of legumine, or vege- 
table caseine, which constitutes about one-fourth of the weight of the peas. 

This solution is not coagulated by heat, but becomes covered with a 
pellicle similar to that which forms upon the surface of boiled milk. It 
is coagulated by acetic acid and by rennet, just as is the case with the 
caseine of milk. 

Sugar of milk, — When whey is evaporated to a small bulk and allowed 



602 



ADULTERATION OF MILK. 



to cool, it deposits hard white prismatic crystals of sugar of milk, or 
lactine (C 12 H 2J 1:? ), which is much less soluble, and therefore less sweet 
than cane-sugar. 

Like this latter it may be converted into grape-sugar (C G H 14 7 ) by 
taking up the elements of two molecules of water when boiled with dilute 
acids. Milk-sugar resembles the other sugars in its capability of combin- 
ing with some bases, such as the alkalies, alkaline earths, and oxide of 
lead ; with the latter it forms two insoluble compounds. 

At about 280° F. the crystals of milk-sugar lose a molecule of water 
and become C 12 H 22 Q U . At 100° F. the sugar fuses, and two molecules 
lose five molecules of water. 

It will be seen that the characteristic constituents of milk are the 
caseine and milk-sugar, but the proportions in which these are present 
vary widely, not only with the animal from which the milk is obtained, 
but with the food and condition of the animal. A general notion of their 
relative quantities, however, may be gathered from the following table, 
exhibiting the results of the analyses made by Boussingault : — 





Cow. 


Ass. 


Goat. 


Woman. 


Water, . . . 


87-4 


90-5 


82-0 


88-4 


Butter, 


4-0 


1-4 


4-5 


2-5 


Milk-sugar, i 
Soluble salts, ) 


5-0 


6-4 


4-5 


4-8 


Caseine, i 
Iusoluble salts, \ 


3-6 


1-7 


9'0 


3-8 



The soluble salts present in milk include the phosphates of potash and 
soda, and the chlorides of potassium and sodium, whilst the insoluble 
salts are the phosphates of lime, magnesia, and oxide of iron. All these 
salts are in great request for the nourishment of the animal frame. 

The milk supplied to consumers living in towns is subject to consider- 
able adulteration ; but in most cases this is effected by simply removing 
the cream and diluting the skimmed milk with water, a fraud which is 
not easily detected, as might be supposed, by determining the specific 
gravity of the milk, for since milk is heavier than water ( 1*032 sp. gr.), 
and the fatty matter composing cream is lighter than water, a certain 
quantity of cream might be removed, and water added, without altering 
the specific gravity of the milk. 

The most satisfactory method of ascertaining the quality of the milk 
appears to consist in setting it aside for twenty-four hours in a tall narrow 
tube (lactometer), divided into 100 equal parts, and measuring the pro- 
portion of cream which separates, this averaging, in pure milk, from eleven 
to thirteen divisions. By shaking milk with a little potash (to dissolve 
the membrane which envelopes the fat globules) and ether, the butter may 
be dissolved in the ether which rises to the surface, and if this be poured 
off and allowed to evaporate, the weight of the butter may be ascertained. 
1000 grains of milk should give, at least, 27 or 28 grains of butter. 
Since, however, the milk of the same cow gives very different quantities 
of cream at different times, it is difficult to state confidently that adultera- 
tion has been practised. It is said that certain yellow colouring matters, 
such as annatto and turmeric, as well as gum, starch, &c, are occasionally 
employed to confer an appearance of richness upon impoverished milk. 



COMPOSITION OF BLOOD GLOBULES. 603 

433. Blood. — The blood from which, the various organs of the body 
directly receive their nourishment is the most important, as well as the 
most complex of the animal fluids. Its chemical examination is attended 
with much difficulty, on account of the rapidity with which it changes 
after removal from the body of the animal. 

On examining freshly drawn blood under the microscope, it is observed 
to present some resemblance to milk in its physical constitution, consist- 
ing of opaque flattened globules floating in a transparent liquid; the 
globules, in the case of blood, having a well-marked red colour. 

In a few minutes after the blood has been drawn, it begins to assume 
a gelatinous appearance, and the seini-solid mass thus formed separates 
into a red solid portion or clot, which continues to shrink for ten or 
twelve hours, and a clear yellow liquid or serum,. It might be supposed 
that this coagulation is due to the cooling of the blood, but it is found by 
experiment to take place even more rapidly when the temperature of the 
blood is raised one or two degrees after it has been drawn ; and on the 
other hand, if it be artificially cooled, its coagulation is retarded. Indeed, 
the reason for this remarkable behaviour of the blood is not yet understood. 

If the coagulum or clot of blood be cut into slices, tied in a cloth, and 
well washed in a stream of water, the latter runs off with a bright red 
colour, and a tough yellow filamentous substance is left upon the cloth ; 
this substance is called fibrine, and its presence is the proximate cause of 
the coagulation of the blood, for if the fresh blood be well whipped with 
a bundle of twigs or glass rods, the fibrine will adhere to them in yellow 
strings, and the defibrinated blood will no longer coagulate on standing. 
If this blood, from which the fibrine has been .extracted, be mixed with 
a large quantity of a saline solution (for example, 8 times its bulk of a 
saturated solution of sulphate of soda), and allowed to stand, the red 
globules subside to the bottom of the vessel. 

These globules are minute bags of red fluid, enclosed in a very thin 
membrane or cell-wall, and if water were mixed with the defibrinated 
blood, since its specific gravity is lower than that of the fluid in the 
globules, it would pass through the membrane (by endosmose), and so swell 
the latter as to break it and disperse the contents through the liquid. 

The red fluid contained in these blood globules consists of an aqueous 
solution, containing as its princijjal constituents a substance known as 
globuline, which very nearly resembles albumen, and the peculiar colour- 
ing matter of the blood, which is called hcemaiine. 

Beside these, the globuies contain a little fatty matter and certain 
mineral constituents, especially the iron (which is associated in some 
unknown form with the colouring matter), the chlorides of sodium and 
potassium, and the phosphates of potash, soda, lime, and magnesia. 

Though the quantities of these constituents are not invariable, even in 
the same individual, the following numbers may be taken as representing 
the average composition of these globules : — 



2-CO 



1000 parts of Blood Globules contain — 

Organic substances of ) 
unknown nature, . ) 
Mineral substances,* . 8 '12 

Exclusive of the iron which is associated with the haematine. 



Water, 


. 688-00 


Globuline, 


. 282-22 


Hseniatine, 


16-75 


Fat, 


2-31 



604 COMPOSITION OF LIQUOR SANGUINIS. 

The mineral substances consist of — 



Potassium, 


. 3-328 


Oxygen, 


. 0-667 


Phosphoric acid, 


. 1-134 


Phosphate of lime, 


. 0114 


Sodium, 


. 1-052 


Phosphate of magnesia, 


. 0-073 


Chlorine, . . ■ . 


. 1-686 


Sulphuric acid, . 


. 0-066 



Globuline is a substance very similar in its character and composition 
to albumen ; it is found also in large proportion in the matter composing 
the crystalline lens of the eye. 

The hcematine or hcematosine must be accounted the most important 
constituent of the blood globules, since it appears to be more intimately 
connected than any other with the functions discharged by the blood in 
nutrition and respiration. 

In order to obtain it in the separate state, the blood globules are boiled 
with alcohol acidulated with sulphuric acid, and the red solution mixed 
with carbonate of ammonia, which separates the greater part of the globu- 
line ; the filtered liquid is evaporated to dryness, and all soluble matters 
are extracted by successive treatments with water, alcohol, and ether. By 
again dissolving the brown residue in alcohol containing ammonia, filter- 
ing, evaporating to dryness, and removing any soluble matter by water, a 
dark brown substance is obtained, which is supposed to be pure hsematine, 
though no longer in the soluble state in which it existed in the blood. It 
is now dissolved only by alkalies or by acidulated alcohol. 

In its chemical composition haamatine is remarkable for the presence 
of iron, associated in a very intimate manner with carbon, hydrogen, 
nitrogen, and oxygen, so that it cannot be recognised by the ordinary 
tests. The formula which has been assigned to it is C 44 H 44 N 6 6 Fe, but it 
is rather doubtful whether it has been analysed in a perfectly pure state. 

The most important chemical property of hgematine is its behaviour 
with oxygen. It is well known that the blood issuing from an artery has 
a much brighter red colour than that drawn from a vein, and that when 
the latter is allowed to coagulate, the upper part of the clot, which is in 
contact with the air, is brighter than the lower part. 

When the dark red blood drawn from a vein is shaken up with air or 
oxygen, a quantity of the latter is absorbed, and a nearly equal volume of 
carbonic acid is disengaged, the dark red colour being at the same time 
changed to the bright red characteristic of arterial blood. The carbonic 
acid exists already formed in the venous blood, and is given off if the' 
blood is exposed under an exhausted receiver. The condition assumed 
by the oxygen when absorbed by the blood is not yet clearly understood, 
but it is generally allowed that the conversion of venous into arterial 
blood is due to the displacement of carbonic acid by oxygen. 

The liquid in which the blood globules float is an alkaline solution con- 
taining albumen, fibrine, and saline matters in about the proportions here 
indicated. 

1000 parts of Liquor Sanguinis contain- — 



Water, . 


. 902-90 


Organic substances of mi- ) „ l( v. 


Albumen, 


78-84 


known nature, . . ) 


Fibrine, . 


4-05 


Mineral substances, . 8 "55 


Fat, 


1-72 





Sodium, . 


. 3-341 


Chlorine, . 


. 3-644 


Potassium, 


0-323 


Oxygen, . 


. 0-403 



PEOTEINE COMPOUNDS. 605 

The mineral substances consist of- — 

Phosphoric acid, . . 0-191 

Sulphuric acid, . . 0*115 

Phosphate of lime, . . 0'311 

Phosphate of magnesia, . 0'222 

The alkaline character of this liquid appears to be due to the presence of 
carbonate and phosphate of soda. 

The albumen present in the serum of blood causes it to coagulate to a 
gelatinous mass when heated, this property being the distinctive feature 
of albumen. This substance may be obtained as a transparent yellow 
mass, resembling gum, and dissolving slowly in water, by evaporating 
either serum of blood or white of egg below 120° F. ; but if the tempera- 
ture be raised above that point, the albumen is coagulated, and cannot be 
redissolved in water unless heated with it under pressure. 

Albumen, like caseine, has never been obtained perfectly free from 
saline matters, particularly the alkaline and earthy phosphates, and much 
difficulty attends the exact determination of its composition. The simplest 
formula which, can be assigned to it is C 108 H 169 N 27 O 34 S. 

It will be remembered that a substance identical with, or very closely 
resembling, albumen, and known as vegetable albumen, is found in those 
vegetable juices which are coagulated by heat. 

Fibrine, as existing in blood, differs from all other animal substances 
by its tendency to spontaneous coagulation. When coagulated it exhibits 
characters very similar to those of coagulated albumen ; but when sepa- 
rated from the freshly drawn blood by violent stirring, it forms elastic 
strings which dry into a yellow horny mass. Fibrine is one of the most 
important constituents of the animal frame, for all muscular flesh consists 
of this substance. The gluten found in the seeds of the cerealia bears a 
very close resemblance to fibrine, and is often called vegetable fibrine. 

The same formula has been often assigned to fibrine as to albumen, and 
its complexity would explain its disposition to putrefy when removed 
from the influence of life. It does not appear quite certain that the 
fibrine dissolved in the blood is identical in jcomposition with that of 
muscular fibre. Some analyses have shown that the muscular fibrine con- 
tains more oxygen than blood-fibrine, and this latter more than albumen, 
affording some ground for the belief that the blood-fibrine represents the 
transition state between the albumen of the serum and the muscular flesh 
into which it is eventually converted. 

Albumen, fibrine, and caseine have been regarded by some chemists 
as compounds of the same primary substance {^pToteine) combined with 
different proportions of sulphur and phosphorus, the proteine being 
isolated by boiling the albuminous body with potash and precipitating the 
solution by an acid. The composition usually assigned to this substance 
is C 18 H 27 jN" 4 6 ; but since it is neither crystallisable nor capable of conver- 
sion into vapour, there is no proof of its purity ; and the great use which 
has been made of this substance by writers on animal chemistry is due to 
the apparent simplicity which it confers upon the relations existing 
between the numerous modifications of albumen, fibrine, and caseine, the 
ultimate formulas of which present so high a degree of complexity. 

In the substance of the brain there has been found a very remarkable 
crystalline substance, which has been termed protagon, and is a complex 
compound of carbon, hydrogen, nitrogen, oxygen, and perhaps phosphorus, 



606 JUICE OF FLESH — KREATINE. 

to whicli no probable formula has yet been assigned. It is very easily 
decomposed, even below 212°. Protagon is insoluble in water, but dis- 
solves in hot alcohol and in acetic acid. When boiled with solution of 
baryta, it yields pliosphngly eerie acid, and a strongly alkaline base neurine. 

Eggs. — The shell of the egg contains about nine-tenths of its weight of 
carbonate of lime, associated with animal matter. The white of egg con- 
sists of albumen (about 12 per cent.), water (about 86 per cent.), and 
small quantities of soluble salts. It is alkaline, from the presence of a 
little soda. Raw white of egg has no smell of sulphuretted hydrogen, 
and does not blacken silver ; but after boiling, both these properties are 
manifested, showing that it suffers some decomposition during coagulation. 

Yolk of egg contains a modification of albumen termed vitelline, and 
owes its colour to a yellow oil which may be extracted with ether, and 
contains phosphoric acid. The yolk of hens' eggs has about half the 
weight of the white, and commonly contains about half its weight of 
water, 16 per cent, of vitelline, 30 per cent, of fat, and 1*5 per cent, of 
saline matters. 

434. Flesh. — The fibrine composing muscular flesh contains about 
three-fourths of its weight of water, a part of which is due to the blood 
contained in the vessels traversing it, and another part to the juice of flesh, 
which may be squeezed out of the chopped flesh. In this juice of flesh 
there are certain substances which appear to play a very important part 
in nutrition. The liquid is distinctly acid, which is remarkable when 
the alkaline character of the blood is considered, and contains phosphoric, 
lactic, and butyric acid, together with kreatine, inosite, and saline matters. 
By soaking minced flesh in cold water and well squeezing it in a cloth, 
a red fluid is obtained containing the juice of flesh mixed with a little 
blood. When the liquid is gently heated, the albumen of the blood and 
of the juice is coagulated in flakes stained with the colouring matter ; 
the liquid filtered from these may be mixed with baryta water to precipi- 
tate the phosphoric acid ; and after a second filtration, evaporated to a 
syrupy consistence and set aside, when beautiful colourless prismatic 
crystals are obtained, consisting of a feeble organic base called 7c?ratine* 
the composition of which is represented by the formula C 4 H 9 N,0. 2 .Aq. 

The quantity of this substance obtained from the flesh of different 
animals varies very considerably, that of fowls having been found hitherto 
most productive, and next that of fish. 1000 parts of the flesh of fowl 
furnished 3'2 parts of kreatine, 1000 parts of cod, 1'71 of kreatine, and 
1000 of beef, - 70 parts. Human flesh is said to contain a large propor- 
tion of kreatine. 

When boiled with acids, kreatine loses the elements of water, and is 
converted into a powerful base called Creatinine (C 4 H 7 N,0), which is also 
found in minute proportion, accompanied by kreatine, in the urine. 

Boiled with alkalies, kreatine gains the elements of water, and furnishes 
two organic bases, urea (also found in urine), and sarcosine (crdpi, flesh). + 

C 4 H B N 3 O a + H,0 = CH 4 N 2 + C,H 7 N0 2 . 

Kreatine. Urea. Sarcosine. 

* From kpeas, flesh. 

+ Sarcosine has been obtained artificially by the action of chloracetic acid on methy- 
laraine ; 

C 2 H 3 C10 2 + NH 2 (CH 3 ) = C 3 H 7 NG 2 + HC1. 
Chloracetic acid. Methylamine. Sarcosine. 



COOKING OF MEAT. 607 

From the concentrated flesh-extract which has deposited the kreatine, 
there may be obtained, by careful treatment, crystals of a sweet substance 
called inosite or sugar of flesh, and having the composition C ti H 1 . 2 O ii .2Aq. 
At a temperature below 212° F. it loses water, and has then the same 
composition as dry grape-sugar, C ( .H 14 O r , with which, however, it is 
certainly not identical. 

Inosite has been obtained in very minute proportion from flesh, but 
unripe beans are said to yield as much as 0*75 per cent, of this interesting 
sugar. 

The saline constituents of the juice of flesh are chiefly phosphates of 
potash, magnesia, and lime, with a little chloride of sodium. 

It is worthy of notice that potash is the predominant alkali in the 
juice of flesh, whilst soda predominates in the blood, especially in the 
serum. 

According to Liebig, the acidity of the juice of flesh is chiefly due to 
the acid phosphate of potash, K 2 0.2H 2 O.P 2 5 , whilst the alkalinity of 
the blood is caused by the phosphate of soda, 2Na 2 O.H 2 O.P 2 5 ; and it 
has been suggested that the electric currents which have been traced in 
the muscular fibres are due to the mutual action between the acid juice of 
flesh and the alkaline blood, separated only by thin membranes from each 
other, and from the substance of the muscles and nerves. 

The average composition of flesh may be represented as follows : — 

Water, 78 

Fibrine, vessels, nerves, cells, \ ,- 

&c, . . ) 

Albumen, . . . . 2 '5 

Other constituents of the { 

juice of flesh, . . ) 



2-5 
100-0 



Liebig 's extract of meat is prepared by exhausting all the soluble matters 
from the flesh with cold water, separating the albumen by coagulation, 
and evaporating the liquid at a steam heat to a soft extract. It contains 
about half its weight of water, 40 per cent, of the organic constituents of 
the juice of flesh (albumen excepted), and 10 per cent, of saline matter. 

Cooking of Meat. — A knowledge of the composition of the juice of flesh 
explains the practice adopted in boiling meat, of immersing it at once in 
boiling water, instead of placing it in cold water, which is afterwards 
raised to the boiling point. In the latter case, the water would soak into 
the meat, and remove the important nutritive matter contained in the 
juice ; whilst, in the former, the albumen in the external layer of flesh is 
at once coagulated, and the water is prevented from penetrating to the 
interior. In making soup, of course, the opposite method should be fol- 
lowed, the meat being placed in cold water, the temperature of which is 
gradually raised, so that all the juice of flesh may be extracted, and the 
muscular fibre and vessels alone left. 

The object to be attained in the preparation of beef-tea, is the extraction 
of the whole of the soluble matters from the flesh, to effect which the 
meat should be minced as finely as possible, soaked for a short time in an 
equal weight of cold water, and slowly raised to the boiling point, at 
which it is maintained for a few minutes. The liquid strained from the 
residual fibrine contains all the constituents of the juice except the albu- 
men, which has been coagulated. 



608 GELATINE — GLUE. 

When meat is roasted, the internal portions do not generally attain a 
sufficiently high temperature to coagulate the albumen of the juice, but 
the outside is heated far above 212° F. ; so that the meat becomes 
impregnated to a greater extent with the melted fat, and some of the 
constituents of the juice in this part suffer a change, which gives rise to 
the peculiar flavour of roast meat. The brown sapid substance thus pro 
duced has been called osmazome* but nothing is really known of its true 
nature. 

In salting meat for the purpose of preserving it, a great deal of the 
juice of flesh oozes out, and a proportionate loss of nutritive matter is sus- 
tained. 

435. Gelatine. — When portions of meat, containing cartilages (gristle) 
or tendons, are boiled for some time with water, the liquid so obtained 
sets to a jelly on cooling. This is due to the presence of gelatine or 
chondrine, or both — substances so nearly resembling each other, that they 
were long confounded under the name of gelatine. The difference in their 
origin is that gelatine is obtained by the action of water at a high tem- 
perature on skin, membrane, and bone,t whilst chondrine is obtained in 
the same way from the cartilages. In their properties there is very little 
difference, the most important being that a solution of chondrine is pre- 
cipitated by acetic acid, by alum, and by acetate of lead, which do not 
precipitate gelatine. 

In composition there is a considerable difference between gelatine and 
chondrine, the latter containing considerably more oxygen and less nitro- 
gen. The simplest formulae which have been assigned to them are — 

Gelatine, . . . C 41 H 67 N 13 16 
Chondrine, . . . C. i6 H 9 N 9 16 ; 

but they both contain phosphates of lime and magnesia in a very intimate 
state of association. 

The characteristic properties of gelatine are the tendency of its solution 
to gelatinise on cooling, and the formation of an insoluble compound with 
tannic acid. The latter is the foundation of the art of tanning (p. 581), 
and the former is turned to account in the preparation of jelly, size, and 
glue. A solution containing only one per cent, of gelatine will set on 
cooling, though if it be repeatedly boiled it loses this property. 

Isinglass is a very pure variety of gelatine prepared from the air bladder 
of fishes, especially of the sturgeon. 

For the manufacture of glue the refuse and parings of hides are gene- 
rally employed, after being cleansed from the hair and blood by steeping 
in lime water, and thoroughly exposed to the air for some days, so as to 
convert the lime into carbonate, and prevent the injurious effect of its 
alkaline character upon the gelatine. They are then boiled with water 
till the solution is found to gelatinise firmly on cooling, when it is run 
off into another vessel, where it is kept warm to allow the impurities to 
settle down, after which it is allowed to gelatinise in shallow wooden 
coolers. The jelly is cut up into slices, and dried upon nets hung up in 
a free current of air. Spring and autumn are usually selected for drying- 
glue, since the summer heat would liquefy it, and frost would, of course, 
split it, and render it unfit for the market. 

* From ocrfjii], odour ; £o>|<xos, soup. 

t The animal matter of bone appears to be isomeric with gelatine; and is called osseine. 



UREA. 609 

Size is made in a similar manner, bat finer skins are employed, and 
the drying is omitted, the size "being used in the gelatinous state. The 
best size is made from parchment cuttings. 

By the action of acids or alkalies upon gelatine, two crystalline organic 
bases may be obtained, known by the names of glycocdll, glycocine, or 
sugar of gelatine (C 2 H 5 N0 2 ), and leucine (C 6 H ]3 N0 2 ). 

It will be seen that glycocine is isomeric with nitrous ether (C 2 H 5 .NO. ) ), 
and leucine with the (at present unknown) nitrous ether of the caproic 
series. Leucine has been found in bullock's lungs and in calf's liver. 

A large number of animal substances very nearly resemble gelatine id 
their composition ; among these are hair, wool, nails, horns, and hoofs. 

Hair contains, in addition to carbon, hydrogen, nitrogen, and oxygen, 
from 3 to 5 per cent, of sulphur. 

Wool has sometimes to be separated from the cotton in worn-out mixed 
fabrics. The mixture is plunged into diluted hydrochloric acid, dried at 
220° F., and submitted to the action of a machine (devil), which removes 
the cotton, rendered brittle by the action of the acid, in the form of dust, 
and leaves the wool fibres untouched. When the object is to save the 
cotton fibre, the fabric is exposed to high-pressure steam, which has no 
action upon cotton, but converts the wool into a brown matter easily 
removed by a beating machine, and sold, for manure, as ulmate of 
ammonia. 

Silk is said to consist of three layers, the outermost consisting of gela- 
tine, and soluble in water ; the next of albumen, soluble in acetic acid on 
boiling ; and the third of a nitrogenised substance called sericine, which is 
insoluble in water and acetic acid. Spider's threads appear to consist of 
this substance. 

Sponge consists of a similar material, which has been called fibroine. 

436. Urine. — The urine of animals is characterised by the presence of 
certain substances which are only met with in very minute quantities, if 
at all, in a state of health, in the other fluids of the body. The most im- 
portant of these are an organic base called urea, uric acid, and Mppuric 
acid. 

Urea. — "When human urine is evaporated to about an eighth of its 
original bulk, and mixed with an equal volume of nitric acid, a semi- 
solid mass is formed consisting of pearly scales of nitrate of urea 
(CH 4 N 2 O.HN0 3 ). If these be washed with cold water, afterwards dis- 
solved in boiling water, and treated with carbonate of baryta, the nitric 
acid combines with the baryta, and the carbonic acid having no tendency 
to combine with the urea, passes off, leaving the urea in solution — 

2(CH 4 N 2 O.HN0 3 ) + BaO.C0 2 - 2CH 4 N 2 + Ba2N0 3 + H 2 + C0 2 . 

Nitrate of urea. * Urea. 

After filtering from the excess of carbonate of baryta, the liquid is 
evaporated on a water-bath, when a mixture of urea and nitrate of baryta 
is obtained, from which the urea may be extracted by hot alcohol. ^ On 
evaporating the alcohol, beautiful prismatic crystals of urea are deposited. 
These crystals, when once separated from the urine in a pure state, may 
be preserved indefinitely even if dissolved in water ; but the urea occur- 
ring in the urine is very soon decomposed, a putrefactive decomposition 
being excited by the mucus, a changeable substance somewhat resembling 
albumen, which collects in feathery clouds in the urine. The change 

2 Q 



610 CONSTITUTION OF UREA. 

which, is thus induced in the urea results in its conversion into carbonate 
of ammonia — 

CH 4 N 2 + 2H 2 = 2NH 3 .H 2 O.CO ? . 

Urea. Carbonate of ammonia. 

It is in consequence of this change that the urine so soon exhales an 
ammoniacal odour. In order to effect the same change in pure urea, it 
is necessary to heat it with water under high pressure. When urea is 
combined with hydrochloric acid, and the hydrochlorate is heated, it 
furnishes hydrochlorate of ammonia and cyanuric acid, according to the 
equation — 

3(CH 4 N 2 0.HC1) = 3(NH 3 .HC1) + H 3 C 3 N 3 3 . 

Hydrochlorate of urea. Cyanuric acid. 

When cyanuric acid is distilled, it yields 3 molecules of hydrated 
cyanic acid (HCNO), and the connexion thus established between urea 
and the cyanogen series becomes intelligible when we see that this base 
is isomeric with cyanate of ammonia (NH 3 .HGNO). In fact, by com- 
bining hydrated cyanic acid with ammonia, and evaporating the solution, 
no cyanate of ammonia, but simply urea, is obtained. 

Upon this has been founded a process for obtaining urea artificially, 
which has attracted a great deal of attention as one of the earliest examples 
of the production in the laboratory, of a complex substance formed in the 
animal body. For the artificial production of urea, 56 parts of well-dried 
ferrocyanide of potassium are intimately mixed with 28 parts of dried 
binoxide of manganese, and the mixture heated to dull redness in an iron 
dish, and stirred until it ceases to smoulder. The oxygen supplied by the 
binoxide of manganese converts the potassium and part of the cyanogen 
of the ferrocyanide into cyanate of potash, the remainder of the cyanogen 
being burnt, and the iron converted into oxide — 

K 4 (CN) 6 Fe + 9 = 4KOTO + 2C0 2 + N 2 + FeO. 

o F f e p T o°taSm e Cyanate of potash. 

On treating the residue with cold water, the cyanate of potash is dis- 
solved out, and after the insoluble portion has subsided, the liquid may 
be poured off, and 41 parts of sulphate of ammonia dissolved in it. Sul- 
phate of potash and cyanate of ammonia are thus formed — 

2KCNO + 2NH 3 .H 2 O.SQ 3 = K 2 O.S0 3 + 2(NH 3 .HCNO); 

and if the solution be evaporated to dryness (on a water-bath) the latter 
salt is transformed into urea, which may be separated from the sulphate 
of potash by alcohol, which dissolves the urea only. 

437. The true constitution of urea has been the subject of much discussion among 
chemists. The circumstance that, under certain conditions, this base assimilates 
the elements of water and is converted into carbonate of ammonia, has led to the 
opinion that urea should be classed among the amides (p. 540), when it would be 
represented as derived from carbonate of ammonia (NH 4 ) 2 O.C0 2 by the loss of water, 
just as oxamide is derived from oxalate of ammonia — 

(NH 4 ) 2 O.C0 2 - 2H 2 = CH 4 N 2 

Carbonate of ammonia. Urea. 

(NH 4 ) 2 C 2 4 - 2H 2 = C 2 H 4 N 2 2 

Oxalate of ammonia. Oxamide. 

The question naturally presents itself, whether the various bases formed by sub- 
stitution from ammonia (p. 530) would furnish corresponding ureas when acted 



COMPOUND UREAS. 611 

upon by cyanic acid. This has been actually found to be the case ; ethylamine 
NH 2 (C 2 H 6 ), for example, acting upon cyanic acid, yields ethyl -urea, which is isomeric 
with the cyanate of ethylamine, just as urea is isomeric with cyanate of ammonia. 

NH 2 (C 2 H 5 ).HCNO = CH 3 (C 2 H 5 )N 2 . 
Cyanate of ethylamine. Ethyl-urea. 

It is evident that if urea be derived from a double molecule of ammonia by the 
substitution of CO for H 2 , then ethyl-urea will be derived in a similar manner from a 
double molecule of ethylamine. 

N 2 H 4 (C 2 H 5 ) 2 N 2 H 3 (C 2 H 5 )(CO)\ 

Ethylamine. Ethyl-urea. 

In this case it will be observed that the diatomic group CO, is substituted for one 
atom of the hydrogen, and for one of its representative, ethyle. 

It will be remembered that the amides can be obtained by the action of ammonia 
upon the corresponding ethers ; thus oxalic ether treated with ammonia gives oxamide, 
and the conversion may be intelligibly repres'ented thus— 



(c 2 2 )"! o . S 2 i w ^p> K h„ 



Oxalic ether. Ammonia. Oxamide. AlcohoL 

In a similar manner, carbonic ether, when heated in a sealed tube with an 
alcoholic solution of ammonia, yields urea and alcohol — 

(CO)" ) H * I < C0 >" ) H 2 

(C 2 H 5 ) 2 p + H 2 |N 2 - H 2 |N 2 + (0aH . )2 

Carhonic ether. Ammonia. Urea. AlcohoL 

When cyanic ether (C 2 H 5 . CNO) is acted on by ammonia, it yields ethyl-urea, the 
action being precisely parallel to that of ammonia upon cyanic acid — 

H.CNO + NH 3 = NH 3 .H;CNO 

Cyanic acid. Urea, 

(C 2 H 5 ).CNO + NH 3 = NH 3 .(C 2 H 5 ).CNO. 
Cyanic ether. Ethyl-urea. 

Many other compound ureas of this description have been obtained, in which the 
hydrogen is partly or entirely replaced by the alcohol radicals. The relation existing 
between these and their prototype, urea, will be seen in the following examples : — 

Urea, CH 4 N 2 



Ethyl-methyl-urea, . . C j CH a 
Tetrethyl-urea, . . . C(C 2 H 5 ) 4 N 2 
Diphenyl-urea, C j ( C Jp) 2 I N 2 . 

The supposition that urea is really constituted upon the ammonia type derives 
some confirmation from the circumstance, that a number of substances have been 
obtained which bear the same relation to urea as the amides do to ammonia. They 
are, therefore, sometimes styled ureides, and sometimes compound ureas, in which a 
negative or acid radical occupies the place of a part of the hydrogen. In illustration 
of the mode of formation of the bodies of this class, the production of benzureide or 
benzoyl-urea may be referred to. 

When ammonia acts upon chloride of benzoyle, it yields benzamide and hydro- 
chloric acid — 

C 7 H 5 0.C1 + NH 3 = C 7 H 5 O.NH 2 + HC1 . 

C S?^T ° f Benzamide. 

benzoyle. 

If urea be substituted for the ammonia, benzureide and hydrochloric acid are 
formed — 

C 7 H 5 0.C1 + CH 4 N 2 = C 7 H 5 O.CH 3 N 2 + HC1 . 

C Wo d y e ie°. f *"■• B — ide ' 



612 UKIC OR LITHIC ACID. 

Both reactions "become much more intelligible if urea and its derivatives be allowed 
to be composed upon the ammonia type — 

NH 3 + (C 7 H 5 0)C1 = NH 2 (C 7 H 5 0) + HC1 
Ammonia. C ^%° f Benzamide. 

N 2 H 4 (CO>" + (C 7 H 5 0)C1 = N 2 H 3 (C 7 H 5 0) (CO)'' + HC1 . 
C £Z%°? Benzureide. 

By similar processes there have been obtained — 

Acetyl-urea, N 2 H 3 (C 2 H 3 0)(CO)" 

Butyryl-urea, . ' N 2 H 3 (C 4 H 7 0)(CO)", &c. 

438. Uric acid. — When human urine is acidified with hydrochloric 
acid and allowed to stand for some time, it deposits minute hard red 
grains, consisting of uric acid (C 5 H 4 N 4 3 ) tinged with the urinary colour- 
ing matter. In urine the acid is present as urate of soda and urate of 
ammonia, which are often deposited from, urine in slight derangements of 
the system, when they are present in excess, these salts being very much 
more soluble in warm water than in cold. Since uric acid and its salts 
are very common ingredients of calculi, this acid is sometimes called lithic 
acid (\idos, a stone). 

As the quantity of uric acid in human urine does not exceed 1 grain 
in 1000, recourse is had to other sources for the preparation of this acid, 
which is now extensively used for the preparation of the murexide 
employed in calico-printing. 

The excrements of the boa-constrictor and of birds, which consist almost 
entirely of acid urate of ammonia, and guano, which has been formed 
by the partial decomposition of the excrements of sea-birds, are excellent 
sources of uric acid. The separation of the uric acid from acid urate 
of ammonia is easily effected by dissolving it in solution of potash, filter- 
ing, and adding hydrochloric acid, when the uric acid, which requires 
10,000 parts of cold water to dissolve it, is precipitated as a white 
crystalline powder. 

When a solution of potash is saturated with uric acid in the cold, and 
boiled down out of contact with air, small needle-like crystals are depo- 
sited, having the composition K 2 .C 5 H 2 N 4 03, and if this be dissolved 
in water, and carbonic acid be passed through the solution, half the potas- 
sium is removed as carbonate, and a granular precipitate of acid urate of 
potash, K.H.C 5 H 2 N" 4 3 is deposited. Uric acid, therefore, is a dibasic 
acid, and the formula of the acid itself (C 5 H 4 JNT 4 3 ) should be written 

When uric acid is added by degrees to strong nitric acid, it dissolves 
with effervescence and evolution of heat ; the solution, on cooling, deposits 
octahedral crystals of a substance called alloxan (C 4 H 4 N 2 5 ), which may 
be represented as formed by the oxidation of the uric acid according to 
the following equation — 

C 5 H 4 N 4 3 + HN0 3 + H 2 = C 4 H 4 N 2 5 + C0 2 + N 2 + NH 3 . 

Uric acid. Alloxan. 

Alloxan has the curious property of staining the fingers of a beautiful 
pink colour, and its solution gives an intense purple colour with sulphate 
of iron. 

A connexion is established, by means of alloxan, between uric acid 
and urea, which becomes important, because these two bodies, accompanied 



HIPPTJEIC ACID. 613 

by a small quantity of alloxan, are always found together in the urine. 
Alloxan appears to be the intermediate stage in the conversion of uric 
acid into urea by oxidation, for if a solution of alloxan be boiled with 
peroxide of lead (Pb0. 2 ) carbonic acid is evolved, and the alloxan is con- 
verted into urea by oxidation — 

C 4 H 4 ff t 6 + 2Pb0 2 - CH 4 N 2 = 3C0 2 + 2PbO. 

Alloxan. Urea. 

When sulphuretted hydrogen is passed through a solution of alloxan, 
the liquid is troubled by the separation of sulphur, and deposits prismatic 
crystals of alloxantine (C 8 H 4 ]Sr 4 7 ) — 

2C 4 H 4 K 2 5 + H 2 S = C 8 H 4 N 4 7 + 3H 2 + S. 

Alloxan. Alloxantine. 

If 4 grains of alloxantine and 7 grains of crystallised alloxan be dissolved 
in hot water, and 80 grains of a cold saturated solution of carbonate of 
ammonia added, the carbonic acid is diseugaged with effervescence, and 
the liquid assumes a brilliant purple colour, depositing as it cools splendid 
crystals, which have a red colour by transmitted light, and reflect a play 
of green and gold, like the wing of the sun-beetle. 

This magnificent substance is known as murexide, and has the formula 

The beautiful colour of murexide has been applied to dyeing and calico- 
printing, being prepared for that purpose from the uric acid furnished by 
guano. 

439. Hippuric acid. — Another acid peculiar to the urine, and found 
in very minute quantity in human urine, is hippuric acid (CgHgNOg), so 
named because it occurs in far larger quantity in the urine of horses (tWos, 
a horse) and cows, the cow's urine yielding more than 1 per cent, of the 
acid. It is generally prepared from cow's urine by evaporating it to about 
an eighth of its bulk, and adding an excess of hydrochloric acid. On 
standing, long prismatic needles of hippuric acid are deposited. It is 
remarkable that this acid can be obtained only from the urine of stall-fed 
cows or of horses kept at rest, for if the animals are actively exercised, 
the above treatment educes benzoic acid (C 7 H 6 0. 2 ) in place of hippuric. 
Again, only the fresh urine yields hippuric acid, for after putrefaction, 
only benzoic acid can be obtained from it. Conversely, if benzoic acid be 
administered to an animal, it makes its appearance as hippuric acid in 
the urine. 

The relation between these two acids becomes evident when hippuric 
acid is boiled for some time with strong hydrochloric acid ; on cooling, 
the solution deposits crystals of benzoic acid, and if the liquid separated 
from these be evaporated, neutralised with ammonia, and mixed with 
alcohol, crystals of glycocoll (p. 609) are obtained. 

C 9 H 9 N0 3 + H 2 = C 7 H 6 2 + C. 2 H 5 M) 2 . 

Hippuric acid. Benzoic acid. Glycocoll. 

This result has been confirmed synthetically by acting upon the com- 
pound resulting from the action of glycocoll on oxide of zinc, with chloride 
of benzoyle (p. 470), when hippuric acid is reproduced. 

Zn.2C 2 H 4 N0 2 + 2(C 7 H 5 0.C1) - ZnCL, + 2C 9 H 9 M) 3 . 

Zinc-glycocoll. Chloride of benzoyle. Hippuric acid. 

Hippuric acid, therefore, may be represented as benzoyl e-glycocoll, 



614 



ULTIMATE ELEMENTS OF PLANTS. 



C 2 H 4 (C 7 H 5 0)N0 2 . A very interesting illustration of the doctrine of 
substitution is connected with these acids. By acting upon hippuric acid 
with nitric and sulphuric acids, it is converted into nitro-hippuric acid by 
the substitution of N0 2 for one atom of its hydrogen, and if this acid be 
boiled with hydrochloric acid, it yields nitrobenzoic acid, just as hippuric 
yields benzoic acid — 



a 



{noj 



NO. 



H o 



Nitro-hippuric acid. 



7 lNd 2 i° 2 

Nitro-benzoic acid. 



c 



(WTO, 

Glycocoll. 



contact with bases, hippuric acid forms salts of the general for- 
M,C Q HJS"Oo, so that the acid itself should be written as 



In 

mula 

hc 9 h 8 no 3 ; 

In addition to the organic substances which have been already men- 
tioned as occurring in the urine (urea, uric acid, mucus, hippuric acid, 
kreatinine), it always contains a large proportion of alkaline and earthy 
salts, especially of chloride of sodium, phosphate and sulphate of potash, 
and phosphates of lime, magnesia, and ammonia. 

The average composition of human urine may be thus stated — 



Water, 

Urea, 

Uric acid, ...... 

Mucus, 

Hippuric acid, kreatinine, ammonia, colouring ) 
matter, and unknown organic matters, . \ 
Chloride of sodium, . 
Phosphoric acid, 
Potash, . . 
Sulphuric acid, 
Lime, .... 
Magnesia, 
Soda, 



956-80 

1423 

0-37 

0-16 

15*03 

7-22 
2-12 
1-93 
1-70 
0-21 
0-12 
0-05 

999-94 



CHEMISTRY OF VEGETATION. 

440. The ultimate elements of plants, that is, the substances with which 
plants must be supplied in one form or other, to sustain their growth, 
are carbon, hydrogen, nitrogen, oxygen, sulphur, phosphorus, chlorine, 
silicon, potassium, sodium, calcium, magnesium, iron, manganese. 

Of these, the carbon, hydrogen, nitrogen, oxygen, sulphur, and phos- 
phorus are grouped together to form the various organic compounds 
furnished by plants, the remaining elements being arranged generally in 
the following forms : — 

Chlorides of potassium and sodium, 

Sulphate of lime, 

Silicates of potash and soda, 

Phosphates of iron (manganese ?), lime, magnesia, and ammonia, 

Compounds of potash, soda, and lime, with vegetable acids. 

Plants are capable of receiving food either in the form of gas through 
the instrumentality of their leaves, or in solution by their roots. 

The carbon, which is their most important constituent as regards quantity, 
is taken up in the form of carbonic acid by both these organs of the 
plant. This carbonic acid is derived either from the surrounding atmo- 



ACTION OF MANURES. 615 

sphere, or from the decay of the organic matters contained in the soil 
which surrounds the roots of the plant. 

The hydrogen is derived partly from water and partly from the am- 
monia which is carried down to the roots of the plant by rain, or is 
evolved in the putrefaction and decay of the nitrogenised organic matters 
of the soil. The ammonia also forms one great source of the nitrogen in 
plants, another being the nitric or nitrous acid, which is either brought 
down by the rain, or formed within the soil by the nitrification of the 
ammonia (p. 129). As to the oxygen, it is obtained both from the car- 
bonic acid and water, which contain this element in larger proportion than 
is ever present in any vegetable product. 

The sulphur and phosphorus contained in the organic parts of the 
plant appear to be chiefly derived from the sulphates and phosphates of 
the soil. 

The chlorine, silicon, and the metals, are derived from the mineral con- 
stituents of the soil. 

It is not difficult to imagine the course of formation of a fertile soil 
from a primary rock (of granite, for example) under the influence of the 
atmosphere and rain, exerted through a very long period. 

It will be remembered that granite consists essentially of quartz (silica), 
feldspar (silicate of alumina and potash or soda), and mica (silicates of 
alumina, iron, potash, and magnesia) ; in addition to these there may 
always be found in granite minute quantities of phosphate of lime, of sul- 
phates, of chlorides, and of manganese. 

By the disintegration of such a rock under the action of air and moisture 
(p. 285), a soil will be formed containing the various mineral substances 
required for the food of the plant. If now, upon the thin layer of soil 
thus formed over the face of the rock, some seeds of the lower orders of 
plants, the lichens, for instance, be deposited, they will grow and fructify, 
deriving their carbon, hydrogen, nitrogen, and oxygen from the air and 
rain, and their mineral constituents from the soil. The death of these 
lichens would add new elements of fertility to the soil, in the shape of the 
food which they had condensed from the air, and of the saline ingredients 
which had been converted within their organisations into forms better 
suited to sustain the higher orders of plants. jGiven, then, the seeds of a 
higher vegetation, a similar process may be supposed to take place, and at 
length animals would be attracted to the spot by the prospect of vegetable 
food, and by transporting to it elements which they had derived from 
other sources, would eventually confer upon it the highest fertility. 
The soil then coming under tillage, the crops raised upon it are consumed 
by animals and removed to a distance, so that the mineral food contained 
in the soil is by degrees exhausted, and unless it is restored the soil be- 
comes barren. 

To restore its fertility is the object of manuring, which consists in add- 
ing to the soil some substance which shall itself serve directly as food for 
the plant, or shall so modify, by chemical action, some material already 
present in the soil, as to convert it into a state in which the plant may 
take advantage of it. 

As examples of substances which are added as direct food for plants, 
may be enumerated : — 

(1.) The ashes of peat, turf, coal, &c, which furnish the mineral sub- 
stances originally obtained from the soil by the vegetables from which 
these materials were formed. 



616 ACTION OF MANURES. 

(2.) Gypsum, or sulphate of lime, and sulphate of magnesia, which ap- 
pear to be valuable not only as sources of sulphur, calcium, and mag- 
nesium, but because they are capable of decomposing the carbonate of 
ammonia, which is either brought down by rain or evolved by putrefaction 
in the soil, and of converting it into sulphate of ammonia which is re- 
tained in the soil, whereas the carbonate, being a volatile salt, would be 
again exhaled into the air and lost to the plants. 

(3.) Phosphate of lime, or bone-ash, which is most commonly con- 
verted into the soluble superphosphate of lime (p.. 224) by treatment with 
sulphuric acid, before being employed as a. manure. 

(4.) Chloride of sodium, or common salt, serves as a source of sodium, 
for in contact with the carbonate of lime, which is found in all fertile 
soils, it is partly converted into carbonate of soda, which may in turn be 
converted into silicate of soda, or any other salt of that alkali necessary 
to the growth of the plant. 

(5.) Mtrate of soda (Peruvian nitre) is held to be of great service in 
some cases, as yielding both soda and nitrogen in a form serviceable to the 
plant. 

(6.) The silicates of potash and soda, which are especially useful to 
crops which, like the cereals, contain a considerable proportion of silica 
in their stems ; since, although that substance is contained in abundance 
in all soils, it is not available for the plant unless converted into a soluble 
state by combination with an alkali. 

(7.) Sulphate of ammonia (derived from the gas-works) is, of course, 
useful both for its sulphuric acid and ammonia. 

(8.) Plants, or parts of plants, ploughed into a soil, would obviously 
furnish food for other plants by their gradual putrefaction and decay. 

(9.) Bones, which furnish carbonic acid and ammonia by the putrefac- 
tion of their gelatinous matter, as well as a large supply of phosphate of 
lime. 

(10.) Urine, yielding much carbonate of ammonia by the decomposition 
of its urea and uric acid, and an abundance of the phosphates and other 
saline matters required by the plant. 

(11.) Solid excrements of various animals, containing the insoluble 
salts (especially phosphates) of the animal's food, as well as easily putres- 
cible organic matters yielding much ammonia and sulphuretted hydrogen. 

(12.) Guano, the dung of carnivorous sea-birds, which owes its very 
high value partly to the large proportion of urate of ammonia and other 
nitrogenised organic substances which it contains, and partly to the pre- 
sence of phosphates and salts of the alkalies. 

(13.) Soot, which appears to act chiefly by virtue of the salts of 
ammonia derived from the destructive distillation of the coal. 

The chief substance employed for acting chemically upon the consti- 
tuents of the soil, so as to render them more serviceable to the plant, is lime, 
which modifies in a very important manner both the organic and mineral 
portions of the soil. Its action upon the former consists in promoting its 
decay, and the conversion of its elements into those forms, viz., carbonic 
acid, water, ammonia, and nitric acid, in which they may be of service to 
the plant. Upon the inorganic constituents of the soil lime acts by 
assisting the decomposition of minerals, particularly of those which con- 
tain the alkalies (such as feldspar), and thus converting them into soluble 
forms. 

in some cases fertility is restored to an apparently exhausted soil, with- 



GROWTH OF PLANTS. 617 

out the addition of manure, by allowing it to lie fallow for a time, so that, 
under the influence of the air and moisture, such chemical changes may- 
take place in it as will again replenish it with food available for the crops. 
It is not even necessary in all cases that the soil should be altogether re- 
leased from cultivation ; for even though it may refuse to feed any longer 
one particular crop, it may furnish an excellent crop of a different 
description, and, which is more remarkable, it may, after growing two or 
three different crops, be found to have regained its power of nourishing 
the very crop for which it was before exhausted. Experience of this has 
led to the adoption of the system of rotation of crops, by which a soil is 
made to yield, for example, a crop of barley, and then successive crops of 
grass, beans, turnips, and barley again. 

The possibility of this rotation is partly accounted for by the difference 
in the mineral food removed from the soil by different crops ; thus turnips 
require much of the alkalies and lime ; wheat, much alkali and silica ; 
barley, much lime and silica; and clover, much lime, so that the soil 
which had been exhausted for wheat, because it no longer contained 
enough soluble silica, might still yield sufficient alkali and lime to a crop 
of turnips, and when the alkali was exhausted, might furnish enough lime 
to a crop of clover, after which, in consequence of the chemical changes 
allowed by lapse of time in the soil, more of the original minerals com- 
posing it might have been decomposed and rendered available for a fresh 
wheat crop. 

Another explanation of the benefit of systems of rotation may be given 
in those cases in which the debris of the preceding crop are allowed to 
remain on the land. Some plants, extending their roots more deeply into 
the soil, avail themselves of mineral food which is beyond the reach of 
plants furnished with shorter roots, and when the refuse of the former 
plants is ploughed into i:he land, the surface is enriched with the food 
collected from the sub-soil. 

Our knowledge of the chemical operations taking place in the plant, 
and resulting in the elaboration of the great variety of vegetable products, 
is very slight indeed. We appear to have sufficient evidence that sugar 
and starch, for example, are constructed in the plant from carbonic acid 
and water, that gluten results from the mutual action of the same com- 
pounds, together with ammonia, or nitric acid, and certain sulphates and 
phosphates, but what the intermediate steps in this conversion may be we 
are not in a position even to hazard a guess. 

All seeds contain starch, gluten, or some similar nitrogenised substance 
(legumine, for example), together with mineral matters, these being pro- 
vided for the nourishment of the young plant until its organs are suffi- 
ciently developed to enable it to procure its own food from the air or from 
the soil. 

During the process of germination, the seed absorbs oxygen and evolves 
carbonic acid, and since the albuminous constituent is the most mutable 
substance present, it is probably this which undergoes oxidation, and 
excites the conversion of the insoluble starch into soluble sugar. At this 
stage the seed requires, as is well known, a fair supply of water, the 
elements of which are required for the conversion of the starch (C 6 H 10 O 5 ) 
into sugar (C, ; H 12 6 ) ; water is also required to dissolve the sugar as well 
as the altered albuminous matter and the mineral salts, in order to form the 
sap of the embryo plant. These constituents of the sap, directed by the 



618 RIPENING OF FKUITS. 

mysterious vital energy in the seed, build up the root, which extends itself 
in search of nourishment down into the soil, and the leaves, which dis- 
charge a similar function with respect to the air. As soon as the leaves 
are developed, the plant becomes able to decompose carbonic acid, water, 
and ammonia, to provide the organic components of its sap. Some part 
of these changes at least appears to take place in the leaves of the plant, 
from which, during the day-time, oxygen (together with a little nitrogen) 
is continually evolved. The leaves have been compared to the lungs of 
animals, the functions of which they reciprocate, for whilst, in the lungs 
of animals, an absorption of oxygen and an evolution of carbonic acid is 
observed, in the leaves of plants, it is the carbonic acid which is absorbed 
and oxygen is disengaged. 

In the dark, plants exhale carbonic acid, but in much smaller quantity 
than they decompose in the light. 

That oxygen must be evolved, if plants construct their carbonaceous 
compounds from carbonic acid and water, is obvious on reflecting that all 
these compounds contain less oxygen, in proportion to their carbon and 
hydrogen, than is contained in carbonic acid and water. 

Thus, we may conceive the formation of all the compounds of carbon 
and hydrogen, or of those elements with oxygen, which are met with in 
plants, by the concurrence, in various proportions, of carbonic acid a ad 
water, and the separation of the whole or a part of their oxygen. 

To take an example ; cellulose (C 6 H 10 O 5 ) would result from the coali- 
tion of 6 mols. of carbonic acid and 5 mols. of water, with separation of 
12 atoms of oxygen. Again, malic acid, C 4 H 6 5 , would require 4 mols. of 
carbonic acid and 3 mols. of water, whilst 6 atoms of oxygen would be 
set free. 

It is equally easy to represent the formation of nitrogenised compounds 
from carbonic acid, water, and ammonia, with separation of oxygen, for 
the nitrogen in all such compounds is present in so small a number of 
equivalents, relatively to the carbon and hydrogen, that the amount of 
oxygen separated from the carbonic acid and water would always far more 
than suffice to convert the whole of the hydrogen of the ammonia into water, 
even if this hydrogen did not itself take part in the formation of the 
compound. Suppose, for instance, that the formation of quinine is to be 
accounted for — 

20CO 2 + 9H 2 + 2NH 3 = C 20 H 24 N 2 O 2 + 47 . 

Quinine. 

If sulphur be a constituent of the vegetable compound to be formed, 
it is conceivable that the sulphuric acid derived from the sulphates pre- 
sent in the soil should co-operate with the carbonic acid, water, and am- 
monia. 

If the composition of gluten be correctly represented by the formula 
CiosHjggNgyO^S, the equation explaining its formation from the above con- 
stituents of the food of the plant would be written — . 



108CO 2 + 44H 2 + 27NH 8 + S0 3 = C 108 H 169 N 27 O 34 S + 0, 






The chemical tendency of vegetables, therefore, is to reduce to a lower 
state of oxidation the substances presented in their food, whilst animals 
exhibit a reciprocal tendency to oxidise the materials on which they feed. 

With respect to the last stage in the existence of the plant, the ripening 



DECAY OF VEGETABLES. 619 

of the fruit, we know a little more concerning the chemical changes which 
it involves. 

Most fruits, in their unripe condition, contain cellulose, starch, and 
some one or more vegetable acids, such as malic, citric, tartaric, and 
tannic, the latter being almost invariably present, and causing the pecu- 
liar roughness and astringency of the unripe fruit. The characteristic 
constituent of unripe fruits, however, is pectose, a compound of carbon, 
hydrogen, and oxygen, the composition of which has not been exactly 
determined. Pectose is quite insoluble in water, but during the ripening 
of the fruit it undergoes a change induced by the vegetable acids, and is 
converted into pectine (C 32 H 40 O 28 ), which is capable of dissolving in water, 
and yields a viscous solution. As the maturation proceeds, the pectine 
itself is transformed into pectic acid (C 16 H 22 15 ), and pectosic acid 
(C 32 H 46 31 ), which are soluble in boiling water, yielding solutions which 
gelatinise on cooling. It is from the presence of these acids, therefore, 
that many ripe fruits are so easily convertible into jellies. 

Whilst the fruit remains green, its relation to the atmosphere appears 
to be the same as that of the leaves, for it absorbs carbonic acid, and 
evolves oxygen ; but when it fairly begins to ripen, oxygen is absorbed 
from the air, and carbonic acid is evolved, whilst the starch and cellulose 
are converted into sugar, under the influence of the vegetable acids (p. 491), 
and the fruit becomes sweet. It has been already seen that the conver- 
sion of starch and cellulose (C 6 H 10 O 5 ) into sugar (C 6 H 12 6 ) would simply 
require the assimilation of the elements of water, so that the absorption of 
oxygen and evolution of carbonic acid are probably necessary for the con- 
version of the tannic and other acids into sugar. For example — 



C 27 H 22 17 + H 2 + 0^ = 

Tannic acid. 


2C 6 H 12 6 + 15C0 2 

Fruit-sugar. 


3C 4 H 6 6 + 3 = C 6 H 12 6 

Tartaric acid. 


+ 3H 2 + 6C0 2 . 



When the sugar has reached the maximum, the ripening is completed ; 
and if the fruit be kept longer, the oxidation takes the form of ordinary 
decay. 

The scheme of natural chemistry would not be complete unless provi- 
sion were made for the restoration of the constituents of plants, after death, 
to the atmosphere and soil, where they might afford food to new genera- 
tions of plants. Accordingly, very shortly after the death of a plant, if 
sufficient moisture be present, the changeable nitrogenised (albuminous) 
constituents begin to putrefy, and chemical motion being thus excited, is 
communicated to the other parts of the plant, under the form of decay, so 
that the plant is slowly consumed by the atmospheric oxygen, its carbon 
being reconverted into carbonic acid, its hydrogen into water, and its 
nitrogen into ammonia, these substances being then transported in the 
atmosphere to living plants which need them, while the mineral consti- 
tuents of the dead plant are washed into the soil by the rain. 

Moist wood is slowly converted by decay into a brown substance, which 
has been called humus, and forms the chief part of the organic matter in 
soils. Alkalies dissolve this substance, and on the addition of an acid 
to the brown solution, a brown precipitate is obtained, which is said to 
contain humic, ulmic, and geic acids, but these substances do not crystal- 
lise, and their existence as definite acids appears to be somewhat doubt- 
ful. Two other acids of a similar kind, crenic and apocrenic acids 



620 FOOD OF ANIMALS. 

(KprjvY], a well), have been obtained from the same source, and are also 
found occasionally in mineral waters. 

When it is desired to preserve wood from decay, it is impregnated with 
some substance which shall form an unchangeable compound with the 
albuminous constituents of the sap. Kreasote (p. 455) and corrosive 
sublimate (kyanising) are occasionally used for this purpose, the wood 
being made to imbibe a diluted solution of the preservative, either by 
being soaked in it or under pressure. 

In Boucherie's process for preserving wood, the natural ascending force 
of the sap is ingeniously turned to account in drawing up the preservative 
solution. A large incision being made around the lower part of the trunk 
of the growing tree, a trough of clay is built up around it, and filled with a 
weak solution of sulphate of copper, acetate of iron, or chloride of calcium. 
Even after the tree has been felled, it may be made to imbibe the pre- 
serving solution whilst in a horizontal position, by enclosing the base of 
the trunk in an impermeable bag supplied with the liquid from a reservoir. 
The impregnation of the wood with such solutions not only prevents 
chemical decay, but renders it less liable to the attacks of insects and the 
growth of fungi. 

NUTRITION OF ANIMALS. 

441. Between the chemistry of vegetable and that of animal life there 
is this fundamental distinction, that the former is eminently constructive, 
and the latter destructive. The plant supplied with compounds of the 
simplest kind — carbonic acid, water, and ammonia — constructs such com- 
plex substances as albumen and sugar ; whilst the animal, incapable of 
deriving sustenance from the simpler compounds, being fed with those of 
a more complex character, converts them eventually, for the most part, 
into the very materials with which the constructive work of the plant 
commenced. It is indeed true, that some of the substances deposited in 
the animal frame, such as fibrine and gelatinous matter, rival in com- 
plexity many of the products of vegetable life ; but for the elaboration 
of these substances, the animal must receive food somewhat approach- 
ing them in chemical composition. It is to this nearer resemblance 
between the food of animals and the proximate constituents of their 
frames, that we may partly ascribe the greater extent of our knowledge 
on the subject of the nutrition of animals, which is, however, far from 
being complete. 

The ultimate elements contained in the animal body are the same as 
those of the vegetable, but the proximate constituents are far more 
numerous and varied. 

The bones containing the phosphates and carbonates of lime and mag- 
nesia, together with gelatinous matter, require that the animal should be 
supplied with food which, like bread, contains abundance of phosphates, 
as well as the nitrogenised matter (gluten) from which the gelatinous 
substance may be formed. In milk, the food of the young animal, we 
have also the necessary phosphates, whilst the caseine affords the supply 
of nitrogenous matters. 

Muscular flesh finds, in the gluten of bread and the caseine of milk, the 
nitrogenised constituent from which its fibrine might be formed with even 
less transformation than is required for the gelatinous matter of bone, 
since the composition of fibrine, gluten, and caseine is very similar. 



CHEMISTRY OF DIGESTION. 621 

The albumen and fibrine of the blood have also their counterparts in 
the gluten and caseine of bread and milk, whilst all the salts of the blood 
may be found in either of these articles of food. 

Bread and milk, therefore, may be taken as excellent representatives of 
the food necessary for animals, and the same constituents are received in 
their flesh diet by animals which are purely carnivorous, but in a higher 
stage of preparation. 

It is natural to suppose that those parts of the frame which contain no 
nitrogen should be supplied by those constituents of the food which are 
free from that element, such as the starch in bread and the sugar and fat 
in milk. 

Before the food can be turned to account for the sustenance of the body, 
it must undergo digestion, that is, must be either dissolved or otherwise 
reduced to such a form that it can be absorbed by the blood, which it 
accompanies into the lungs to undergo the process of respiration, and thus 
to become fitted to serve for the nutrition of the various organs of the 
body, since these have to be continually repaired at the expense of the 
constituents of the blood. 

The first step towards the digestion of the food is its disintegration, 
effected by the teeth with the aid of the saliva, by which it should be 
reduced to a pulpy mass. The saliva is an alkaline fluid characterised by 
the presence of a peculiar albuminous substance called pty aline (tttvw, to 
spit), which easily putrefies. The action of saliva in mastication is 
doubtless in great part a mechanical one, but it is possible that its 
alkalinity assists the process chemically, by partly emulsifying the fatty 
portions of the food. The liability of ptyaline to putrefaction favours the 
supposition that it may act in some way as a ferment in promoting the 
digestion. 

This disintegration of the food is of course materially assisted by the 
cooking to which it has been previously subjected, the hard and fibrous 
portions having been thereby softened. 

The food now passes to the stomach, in which it remains for some time, 
at the temperature of the body (98° F.), in contact with the gastric juice, 
the chief chemical agent in the digestive process. 

The gastric juice, which is secreted by the lining membrane of the 
stomach, is an acid liquid, containing hydrochloric and lactic acids. It is 
characterised by the presence of a peculiar substance belonging to the 
albuminous class of bodies, which is called pepsine (^eWco, to digest), and 
possesses the remarkable power of enabling dilute acids, by its mere 
presence, to dissolve such substances as fibrine and coagulated albumen, 
which would resist the action of the acid alone for a great length of time. 

An imitation of the gastric juice may be made by digesting the mucous 
membrane of the stomach for some hours in warm very dilute hydrochloric 
acid. The acid liquid thus obtained is capable of dissolving meat, curd, 
&c, if it be maintained at the temperature of the body. The pepsine 
prepared from the stomach of the pig and other animals is sometimes 
administered medicinally in order to assist digestion. 

The principal change which the food suffers by the action of the gastric 
juice is the conversion of the fibrinous and albuminous constituents into 
soluble forms ; the starch is also partly converted into dextrine and sugar, 
but the fatty constituents are unchanged. 

The food which has thus been partially digested in the stomach is called 
by physiologists chyme, and passes thence into the commencement of the 



622 BILE. 

intestines (the duodenum), where it is subjected to the action of two more 
chemical agents, the bile and the pancreatic juice. 

Bile consists essentially of a solution of two salts known as glycocholate 
and taurocholate of soda. Both glycocholic and taurocholic acids are 
resinous, and do not neutralise the alkali, so that the bile has a strong 
alkaline character. Another characteristic feature of this secretion is the 
large proportion of carbon which it contains. Glycocholic acid has the 
composition HC 26 H 42 N0 6 , and contains therefore 67 per cent, of carbon, 
whilst taurocholic acid, HC 26 H 44 N0 7 S, contains 61 per cent. The names 
of these acids have reference to the circumstance that they furnish respec- 
tively glycocoll and taurine, together with two new acids free from nitro- 
gen, when they are boiled with dilute hydrochloric acid — 



2HC 26 H 42 N0 6 + H 2 = C 48 H 78 9 + 2C 2 H 5 NO 

Glycocholic acid. ^acid^ Glycocoll. 



HC 2 ,H 14 N0 7 S + H s O = C 2 H,N0 3 S + HC M H»0„. 

Taurocholic acid. Taurine. Cholic acid. 

Taurine forms colourless crystals of great beauty, and is remarkable for 
the large proportion (above 25 per cent.) of sulphur which it contains. 
It also presents an interesting example of a complex animal derivative, 
which may be artificially prepared in a very simple manner. 

When olefiant gas is passed over anhydrous sulphuric acid, it is absorbed, 
and if the product be dissolved in water, neutralised with ammonia and 
evaporated, crystals of isethionate of ammonia, are obtained — 

C 2 H 4 + S0 3 + KH 3 + H 2 = NH 3 ,H 2 O.C 2 H 4 S0 3 . 

Isethionate of ammonia. 

When this salt is moderately heated, it loses a molecule of water, and 
leaves taurine — 

NH :i .H 2 O.C 2 H 4 S0 3 - H 2 - C 2 H^ T 3 S. 

Isethionate of ammonia. Taurine. 

Another characteristic ingredient of the bile is cholesterine * (C 2r H 41 0), 
a crystalline substance somewhat resembling the fats, and often deposited 
in large quantity in the form of biliary calculi. It has also been found 
in pease, wheat, and some vegetable oils. 

The peculiar colouring matter of the bile has never been obtained in a 
pure state. 

A peculiar substance called glycogen, or animal starch (0 6 H 10 O 5 ), has 
been found in the liver, and becomes speedily converted into sugar after 
death, by assimilating the elements of water. 

The special function of the bile in the digestion of the food has not 
been explained, bat from its strongly alkaline reaction it does not appear 
improbable that it assists in the digestion of fatty substances. 

The pancreatic juice is another alkaline secretion, which differs from 
the bile in containing a considerable quantity of albumen, and is very 
putrescible. Its particular office in digestion appears to consist in promot- 
ing the conversion of the starchy portions of the food into sugar (p. 491), 
though it also has a powerful action upon the fats, causing them to form 
an intimate mixture, or emulsion, with water, and partly saponifying 

* From x°^v, bile; vreap, fat. 



CHEMIST11Y OF NUTRITION. 623 

them. The digestion of the starch and sugar is completed by the action 
of the intestinal fluid in the further passage of the food through the 
intestines, so that when it arrives in the small intestines, all the soluble 
matters have become converted into a thin milky liquid called chyle, 
which has next to be separated mechanically from the insoluble portions, 
such as woody fibre, &c, which are excreted from the body. 

This separation is effected in the small intestines by means of two dis- 
tinct sets of vessels, one of which (the mesenteric veins) absorbs the dis- 
solved starchy portions of the food, and conveys them to the liver, whence 
they are afterwards transferred to the right auricle of the heart. The 
other set of vessels (lacteals) absorbs the digested fatty matters, and 
conveys them, through the thoracic duct, into the subclavian vein, and 
thence at once into the right auricle of the heart. 

From the right auricle this imperfect blood passes into the right 
ventricle of the heart, and is there mixed with the blood returned from 
the body by the veins, after having fulfilled its various functions in the 
system. The mixture, which has the usual dark-brown colour of venous 
blood, is next forced by the contraction of the heart, into the lungs, 
where it is distributed through an immense number of extremely fine 
vessels traversing the lungs, in contact with the minute tubes containing 
the inspired air, so that the venous blood is only separated from the 
air by very thin and moist membranes. Through these membranes 
the dark venous blood gives up the carbonic acid with which it had 
become charged by the oxidation of the carbon of the organs, in its 
passage through the body, and acquires, in return, about an equal 
volume of oxygen, which converts it into the bright crimson arterial 
blood. In this state it returns to the left side of the heart, whence 
it is conveyed, by the arteries, to the different organs of the body. 

The chemistry of th.3 changes effected and suffered by the blood in 
its circulation through the body is very imperfectly understood. One 
of its great offices is the supply of the oxygen necessary to oxidise 
the components of the various organs, and thus to evolve the heat 
which maintains the body at its high temperature. The results of the 
oxidation of these organs are undoubtedly very numerous ; among them 
we may trace carbonic (C0 2 ), sulphuric (SO'), phosphoric (P 2 5 ), lactic 
(C 3 H 6 3 ), butyric (C 4 H 8 2 ), and uric (C 5 H 4 N 4 3 ) acids, as well as urea 
(CH 4 ]Sr 2 0), and some other substances. The destroyed tissues must at the 
same time be replaced by the deposition, from the blood, of fresh particles 
similar to those which have been oxidised. In the course of the blood 
through the circulation, the above products of oxidation have to be 
removed from it — the carbonic acid by the lungs and skin — the sulphuric, 
phosphoric, and uric acids, and the urea, by the kidneys. 

The various liquid secretions of the body, such as the bile, the saliva, 
the gastric juice, &c, have also to be elaborated from the blood during its 
circulation through the arteries, after which it returns, by the veins, to 
the heart, to have its composition restored by the matters derived from 
the food, and to be reconverted into arterial blood in the lungs. 

When it is remembered that the body is exposed to very considerable 
variations of external heat and cold, a question occurs as to the provision 
made for maintaining it at its uniform temperature. This is effected 
through the agency of the fat which is deposited in all the organs of the 
body. Since fatty substances in general are particularly rich in carbon 
and hydrogen, their oxidation within the body would be attended with 



624 CHEMISTRY OF FOOD. 

the production of more heat than that of those parts of the organs which 
contain much nitrogen and oxygen. Accordingly, when the body is 
exposed to a low temperature, a larger quantity of its fat is consumed by 
the oxidising action of the blood, and a corresponding increase takes 
place in the amount of heat evolved, thus compensating for the greater 
loss of heat suffered by the body in the cooler atmosphere. Of course, 
in cold weather, when more oxygen is required to maintain the heat of 
the frame, a larger quantity of that gas is inhaled at each breath, on 
account of the higher specific gravity of the air, in addition to which we 
have the quickened respiration which always attends exposure to cold. 

To supply this extra demand for carbon and hydrogen in cold weather, 
we instinctively have recourse to such substances as fat, starch, sugar, 
&c, which contain those elements in large proportion, and these aliments, 
free from nitrogen, are often spoken of as the respiratory constituents of 
food ; whilst flesh, gluten, albumen, &c, which contain nitrogen, are styled 
the plastic elements of nutrition (jrXdo-o-oi, to form). 

Bearing in mind that the food has a twofold office — to nourish the 
frame and to maintain the animal heat — it will be evident that a judiciously 
regulated diet will contain due proportions of those nitrogenous consti- 
tuents, such as albumen, fibrine, and caseine, which serve to supply the 
waste of the organs, and of such non-nitrogenised bodies as starch and 
sugar, from which fat may be elaborated to sustain the bodily warmth. 

The proportion which these two parts of the food should bear to each 
other will, of course, depend upon the particular condition of existence 
in the animal. Thus, for a growing animal, a larger proportion of the 
nitrogenised or plastic portion of food would be required than for an 
animal whose growth had ceased ; and animals exposed to a low tempera- 
ture would require more of the non-nitrogenised or heat-giving portions of 
the food. 

Accordingly, we find that a man can live upon a diet which contains 
(as in the case of wheaten bread) five parts of non-nitrogenised (starch 
and sugar) to one part of nitrogenised food (gluten) ; whilst an infant, 
whose increasing organs require more nitrogenised material, thrives upon 
milk, in which this amounts to one part (caseine) for every four parts of 
the non-nitrogenised portion (milk-sugar and fat). 

The inhabitants of cold climates consume, as is well known, much 
more oil and fat than those of the temperate and hot regions. 

An examination of the composition of different articles of food affords 
us an explanation of the custom which experience has warranted, of asso-. 
dating particular varieties of food. Thus, assuming as our standard of 
comparison the composition of bread, which contains one of nutritive to 
five of heat-giving matter, the propriety of associating the following kinds 
of food will be appreciated : — 



Beef . 

Potatoes, 


Nutritive. 
. 1 
. 1 


Heat-giving. 

1-7 

10 


Ham, . 
Veal, . 


. 1 
. 1 


3 

01 


Mutton, 
Rice, . 


. 1 
. 1 


27 
12'3 



All muscular or mental exertion is attended with a corresponding 



CHANGES AFTER DEATH. 625 

oxidation of the tissues of the frame, just as each movement of a steam- 
engine may be traced to the combustion of a proportionate quantity of 
coal under the boiler ; and hence such exertion both creates a demand 
for food, and quickens the respiration to obtain an increased supply of 
oxygen. 

Experiment has proved that the proportion which the oxygen consumed 
in respiration bears to the carbonic acid exhaled, depends very much upon 
the nature of the food. Thus an animal fed upon vegetable matters, such 
as starch and sugar (the oxygen in which exactly suffices to convert the 
hydrogen into water), will turn nearly all the inspired oxygen to account 
in the formation of carbonic acid, the volume of which will be nearly 
equal to that of the oxygen which disappears at each inspiration; but when 
flesh, or particularly fat, is consumed, much more of the inspired oxygen 
is required to convert the hydrogen of the food into water, so that the 
volume of the carbonic acid is far less than that of the oxygen consumed 
in respiration. When an animal has been kept for a length of time 
without food, the proportion between the volume of the carbonic acid 
and that of the oxygen consumed, is the same as if the animal were being 
fed upon a flesh diet, inasmuch as its own flesh alone is now supporting 
its respiration. 



CHANGES IN THE ANIMAL BODY AETEE DEATH. 

442. After the death of animals, just as after that of plants, their com- 
ponent parts are reduced to the primary forms from which they were 
derived, so that they may begin again at the foot of the ascending scale 
of life. Yery soon after life is extinct, the atmospheric oxygen begins 
to induce a change in some of the nitrogenous constituents, and this 
change is soon communicated to all parts of the body, which undergo 
a putrefaction or metamorphosis, of which the ultimate results are the 
conversion of the carbon into carbonic acid, the hydrogen into water, 
the nitrogen into ammonia, nitrous and nitric acids, and the sulphur 
into sulphuretted hydrogen and sulphuric acid. " The mineral constituents 
of the animal frame then mingle with the surrounding soil, and are 
ready to take part in the nourishment of plants, which construct the 
organic components of their frames from the carbonic acid and ammonia 
furnished by the putrefaction of the animal, and then serve in their turn 
as sustenance for animals whose respiration supplies the air with carbonic 
acid, and takes in exchange the oxygen eliminated by the plant. 

The functions of the two divisions of animate nature are, therefore, 
perfectly reciprocal, and this relationship must be regarded as the founda- 
tion of economical agriculture. 

If it were possible to prevent the change of the atmosphere, it is quite 
conceivable that a perpetual succession of plants and animals could be 
raised upon a given farm without any importation of food, provided that 
there was also no exportation. Or even, permitting an exportation of 
food, the succession of plants and animals raised upon the same land 
might be, at least, a very long one, if the solid and liquid excrements of 
the animals, to feed whom this exportation took place, were restored to the 
land upon which this food was raised. The explanation of this is, that 
the solid and liquid excrements of the animal contain a very large propor- 

2 R 



626 NATURE OF PUTREFACTION. 

tion of the mineral constituents of the soil, in the very state in which 
they are best fitted for assimilation by the crop, and as long as the soil 
contains the requisite supply of mineral food, the plant can derive its 
organic constituents from the atmosphere itself. 

Forasmuch, however, as the vegetable and animal food produced upon 
a farm is generally exported to feed the dwellers in towns, whose excre- 
ments cannot, without excessive outlay, be returned to the soil whence 
the food was derived, it becomes necessary for the agriculturist to pur- 
chase farm-yard manure, guano, &c, in order to prevent the exhaustion of 
his soil. A great manufacturing country, in which the majority of the 
inhabitants are congregated in very large numbers around a few centres 
of industry, at a distance from the land under tillage, is thus of necessity 
dependent for a considerable proportion of its food upon more thinly 
populated countries where manufactures do not flourish, to which it ex- 
ports in return the produce of the labour which it feeds. 

The parts of the frames of animals differ very considerably in their 
tendency to putrefaction. The blood and muscular flesh undergo this 
change most readily, as being the most complex parts of the body, whilst 
the fat remains unchanged for a much longer period, and the bones and 
hair will also resist putrefaction for a great length of time. 

The comparative stability of the fat is observed in the bodies of animals 
which have been buried for some time in a very wet situation, when they 
are often found converted almost entirely into a mass of adijwcere, con- 
sisting of the stearic and margaric acids derived from the fat. 

When an animal body is thoroughly dried, it may be preserved un- 
changed for any length of time, and this is the simplest of the methods 
adopted for the preservation of animal food, becoming far more efficacious 
when combined with the use of some antiseptic substance such as salt, 
sugar, spice, or kreasote. 

The preservative effects of salt and sugar are sometimes ascribed to the 
attraction exerted by them upon moisture, which they withdraw from the 
flesh, whilst spices owe their antiseptic power to the essential oils, which 
appear to have a specific action in arresting fermentative change, a cha- 
racter which also belongs to kreasote, carbolic acid, and probably to other 
substances which occur in the smoke of wood, well known for its efficacy 
in curing animal matter. 

A process commonly adopted for the preservation of animal and vege- 
table food consists in heating them with a little water in tin canisters, 
which are sealed air-tight as soon as the steam has expelled all the air, 
and if the organic matter be perfectly fresh, this mode of preserving it is 
found very successful, though, if putrefaction has once commenced, to ever 
so slight an extent, it will continue even in the sealed canister, quite in- 
dependently of the air. 

Modern experiments have disclosed a great imperfection in our acquaint- 
ance with the conditions under which putrefaction takes place, and appear 
to indicate the presence in the atmosphere of some minute solid particles 
which appear to be minute ova or germs, and have the power of inducing 
the commencement of this change. It has been found that milk, for 
example, may be kept for a very considerable period without putrefying, 
if it be boiled in a flask, the neck of which is afterwards loosely stopped 
with cotton wool, whilst, if the plug of cotton wool be omitted, the other 
conditions being precisely the same, putrefaction will take place very 
speedily. 



NATUKE OF PUTKEEAUTION. 627 

Perfectly fresh, animal matters have also been preserved for a length of 
time in that state, in vessels containing air which has been passed through 
red-hot tubes with the view of destroying any living germs which might 
be present, and such substances have been found to putrefy as soon as the 
unpurined air was allowed access to them. 

The extremes of the scale of animated existence would appear to meet 
here. The highest forms of organised matter, immediately after death, 
serve to nourish some of the lowest orders of living germs, these helping 
to resolve the complex matter into the simpler forms of carbonic acid, 
ammonia, &c, which are returned to the atmosphere, the great receptacle 
for the four chief elements of living matter. 



628 



ATOMTC WEIGHTS. 



ATOMIC WEIGHTS 



Aluminum, . 


. Al 


27-5 


Molybdenum, . Mo 


96 


Antimony, 


. Sb 


122 


Nickel, 


." Ni 


59 


Arsenic, 


. As 


75 


Niobium, 


. Nb 


94 


Barium, 


. Ba 


137 


Nitrogen, 


. N 


14 


Bismuth, 


. Bi 


210 


Osmium, 


. Os 


199 


Boron, 


. B 


10-9 


Oxygen, 


. O 


16 


Bromine, 


. Br 


80 


Palladium, 


. Pd 


106-5 


Cadmium, 


. Cd 


112 


Phosphorus, 


. P 


31 


Csesium, 


. Cs 


133 


Platinum, 


. Pt 


197-1 


Calcium, 


. Ca 


40 


Potassium, 


. K 


391 


Carbon, 


. C 


12 


Rhodium, 


. Ro 


104-3 


Cerium, 


. Ce 


92 


Rubidium, 


. Rb 


85-3 


Chlorine, 


. CI 


35-5 


Ruthenium, 


. Ru 


101-2 


Chromium, 


. Cr 


52-5 


Selenium, 


. Se 


79-5 


Cobalt, 


. Co 


59 


Silicon, 


. Si 


28 


Copper, 


. Cu 


63-5 


Silver, 


. . Ag 


108 


Didymium, 


: Di 


96 


Sodium, 


. Na 


23 


Erbium, 


. E 


112-6 


Strontium, 


. Sr 


87-5 


Eluorine, 


. F 


19 


Sulphur, 


. S 


32 


Glucinum, 


. G 


9-5 


Tantalum, 


. Ta 


182 


Gold, . 


. Au ' 


196-6 


Tellurium, 


. Te 


129 


Hydrogen, 


. H 


1 


Thallium, 


. Tl 


204 


Indium, 


. In 


75-6 


Thorinum, 


. Th 


238 


Iodine, 


. I 


127 


Tin, . 


. Sn 


118- 


Iridium, 


. Ir 


197-1 


Titanium, 


. Ti 


50 


Iron, . 


. Ee 


56 


Tungsten, 


. W 


184 


Lanthanium 


, . La 


92 


Uranium, 


. U 


120 


Lead, . 


. Pb 


207 


Vanadium, 


. V 


51-3 


Lithium, 


. L 


7 


Yttrium, 


. Y 


.61:7 


Magnesium, 


• • Mg 


24-3 


Zinc, . 


. Zn 


65 


Manganese, 


. Mn 


55 


Zirconium, 


. Zr 


89-5 


Mercury, 


• Hg 


200 









INDEX. 



The names of minerals are printed in italics. 



Abel's experiments on gun-cotton, 500. 
fuze-composition, 316. 
gun-cotton pulp, 496. 
Acetal, 546. 
Acetamiole, 541. 
Acetic acid, HC 2 H 3 2 , 461. 

artificial formation, 525. 
formed from alcohol, 487. 
formed from citric, 580. 
glacial, HC 2 H 3 2 , 556. 
purification, 461. 
synthesis of, 559. 
anhydride, C 4 H 6 3 , 556. 
ether, 515. 
oxychloride, 556. 
peroxide, 557. 
Acetification, 487. 
Acetine, 572. 
Acetone, C 3 H 6 0, 555. 

diethylated, 560. 
dimethylated, 560. 
ethylated, 560. 
methylated, 560. 
properties, 555. 
Acetones, 548. 
Acetonitrile, 541. 
Acetyle, 547. 

chloride, 556. 
peroxide, 557. 
urea, 612. 
Acetylene, C 2 H 2 , 89. 

copper test for, 89. 
detection in coal-gas, 109. 
formed from olefiant gas, 94. 
preparation from coal-gas, 89. 

ether, 91. 
properties, 91. 
silver precipitate, 90. 
synthesis, 89. 
Acetylide of copper, preparation, 90. 
potassium, 91. 
sodium, 91. 
Acid, 25. 

definition, 10. 
etymology of, 10. 
of sugar, 575. 
unitary definition, 253. 
Acids, acrylic series of, C H H2n-20. 2 , 567. 
anhydrous, 42. 
aromatic, 455, 537. 
dibasic, constitution, 254. 

unitary definition, 254. 
hydrated, 42. 
monobasic, constitutiou, 254. 

unitary definition, 254. 



Acids of the acetic series, 507. 
lactic series, 552. 
organic, constitution, 556. 
oxalic series of, 571. 
polybasic, 517. 
tribasic, constitution, 254. 

unitary definition, 254. 
vegetable, 574. 
volatile, separation, 561. 
water-type view of, 255. 
Acidulous waters, 49. 
Aconitic acid, 580. 
Aconitine, 529. 
Acrylic acid, HC 3 H 3 2 , 567. 
Actinic rays of light, 146. 
Adapter, 89. 
Additive formulae, 83. 
Adipic acid, 571. 
Adipocere, 626. 
Aerated bread, 489. 
After-damp, 74. 
Ag, silver, 359. 
AgBr, bromide of silver, 363. 
AgCl, chloride of silver, 363. 
Agl, iodide of silver, 363. 
AgN0 3 nitrate of silver, 362. 
Ag 2 0, oxide of silver, 362. 
Agriculture, economy of, 634. 
Ag 2 S sulphide of silver, 364. 
Agate, 109. m 
Aich-metal, 341. 

Air, analysis of by eudiometer, 34. 
by nitric oxide, 137. 
by phosphorus, 55. 
by pyrogallic acid, 583. 
atmospheric, 54. 
benzolised for illuminating, 105. 
burnt in coal-gas, 102. 
candle test applied to, 74. 
effect of combustion on, 74. 
effect of electric sparks on, 129. 
eudiometric analysis, 34. 
exact analysis by copper, 55. 
germs of life in, 626. 
proportion of ammonia in, 119. 
Al, aluminum, 284. 
A1,0 3 , alumiiia, 287. 
Alabaster, 278. 

oriental, 47. 
Albite, 290. 

Albumen of blood, 605. 
Alcarsin, 521. 
Alcohol, C 2 H 6 0, 509. 
absolute, 510. 
allylic, 475, 



630 



INDEX. 



Alcohol, amylic, C 5 H 12 0, 505. 
anisic, 550. 
benzoic, 550. 
caprylic, 572. 
eery lie, 573. 
chemical constitution, 518. 

definition, 506. 
cuminic, 550. 
flame, 105. 
from milk, 600. 
methylated, 468. 
methylic, CH 4 0, 461. 
radicals, C M H2» + i, 512. 

doubled formulae, 513. 
synthesis, 518. 
water-type view, 518. 
Alcoholic fermentation, 485. 
Alcohols and their derivatives, 505. 
boiling points, 506. 
diatomic, 550. 
general properties, 506. 
monatomic, 550. 

table of, 505. 
polyatomic, 550. 
triatomic, 554. 
vapour-densities, 506. 
Aldehyde, acetic or vinic, C 2 H 4 0, 545. 
ammonia, NH 3 , C 2 H 4 0, 546. 
benzoic, 549. 
butyric, 547. 
caprylic, 548. 
chemical constitution, 546. 
cinnamic, 550. 
cuminic, 550. 
euodic, 548. 

formation in vinegar-making, 487. 
lauric, 548. 
cenanthic, 548. 
preparation, 546. 
properties, 546. 
propionic, 548. 
pyromucic, 558. 
resin, 546. 
rutic, 548. 
salicylic, 550. 
valeric, 548. 
Aldehydes, 545. 

action on amines, 548. 
derivation from alcohols, 506. 
Alder- wood, composition, 413. 
Ale, composition, 486. 
Algaroth, powder of, 377. 
Alizarine, artificial, 592. 
Alkali, definition, 10. 

manufacture, 263. 
metals, group of, 274. 
works, fumes from, 154. 
Alkaline earth metals, general review, 282. 
Alkaloids, constitution, 530. 

determined, 535. 
organic, 529. 

vegetable, extraction of, 584. 
Allotropy, 192. 
Alloxan, C 4 H 4 N 2 5 , 612. 
Alloxantine, C 8 H 10 N 4 O 10 , 612. 
Allyle, C 3 H„ 474. 
iodide, 474. 
series, 474, 567. 
sulphide, 474. 
sulphocyanide, 474. 
terbromide, 568. 
Allylene, 475. 



Allylic alcohol, 475. 

aldehyde, 567. 
Almond cake, 469. 

oil, 571. 
Almonds, 469. 
Aloes, 475. 
Aludels, 365. 
Alum, 286. 

basic, 287. 
concentrated, 286. 
in bread, 490. 
shale, 286. 
uses, 287. 
Alumina, Al 2 3 , 287. 
acetate, 555. 

action of fluoride of silicon on, 185. 
hydrate, 288. 
phosphates, 291. 
silicates, 289. 
sulphate, 286. 
Aluminite, 252. 
Aluminum, Al, 284. 

action on water, 12. 
and copper, 289. 
bronze, 289. 
chloride, Al 2 Cl e , 288. 
ethide, 526. 
extraction, 288. 
fluoride, 185. 
methide, 526. 
properties, 289. 
silicide, 114. 
Alums, 212, 287. 

Amalgam for electrical machines, 366. 
of ammonium, 126. 
of sodium, 126. 
Amalgamating zinc plates, 366. 
Amalgamation of gold ores, 398. 
of silver ores, 359. 
Amalgams, 366. 
Amarine, 558. 
Amber, 467. 
Amethyst, 109, 324. 
Amides, constitution, 542. 
formation, 540. 
of phosphoric acid, 238. 
Amidide of potassium, 542. 
Amidodiphenylimide, 454. 
Amidogen, NH 2 , 542. 
Ammonia, NH 3 , 119. 

absorbed by charcoal, 63. 

absorption by water, 121. 

action of iodine on, 180. 

-alum, 287. 

and chlorine, 149. 

arsenite, 243. 

as food for plants, 120. 

bicarbonate, 269. 

bihydrosulphate, 271. 

bisulphate, 269. 

burnt in oxygen, 124. 

carbonate, (NH 4 ) 2 O.C0 2 , 269 

combination with acids, 125. 

common carbonate, 2(NH 4 ) 2 0. 

3C0 2 ,269. 
composition, 126. 
decomposed by the spark, 125. 
delicate test for, 370. 
explosion with oxygen, 128. 
formation from nitric acid, 133. 
gas, dried, 123. 

preparation, 120. 



INDEX. 



631 



Ammonia group of hydrogen compounds, 246 
hydriodate, 180, 271. 
hydrobromate, 271. 
hydrochlorate, NH 3 .HC1, 120. 
properties, 270. 
hydrosulphate, NH 3 .H 9 S, 271 
hyposulphite, 271. 
identified, 121. 

in waters, examination for, 370. 
isethionate, 622. 
liquefied, 123. 
molybdate, 387. 
muriate, 270. 
Nessler's test for, 370. 
nitrate, 136. 

decomposed by heat, 136. 
preparation, 136. 
nitrification of, 129. 
oxalate, (NH 4 ) 2 C 2 4 , 576. 
properties, 121. 
proportion in air, 119. 
salts, 268. 
sesquicarbonate, 2(NH 4 ) 2 0.3C0 2 , 

269. 
solution, determination of 

strength, 122. 
solution, specific gravity, 122. 
sources of, 120. 
sulphate, (NH 4 ) 2 O.S0 3 , 269. 
urate, 621. 
volcanic, 266. 
Ammoniacal liquor, 444. 

extraction of ammonia 
from, 120. 
Ammoniacum, 475. 
Ammonia-meter, 122. 
Ammonias, complex, 530. 

ethylated, 530. 
Ammoniated chloride of silver, 123. 
Ammonide, sulphuric, (NH 3 ) 2 b0 3 , 268 
Ammonium, NH 4 , 268. 

amalgam, 126. 
bisulphide, 271. 
bromide, 271. 
chloride, 270. 

properties, 270. 
heptasulphide, 271. 
iodide, 271. 
oxide, (NH 4 ) 2 0, 268. 
pentasulphide, 271. 
sulphide (NH 4 ) 2 S, 271. 

yellow, 271. 
sulphocyanide prepared, 218. 
theory, 125. 
Amorphous, 60. 
Amorphous phosphorus, 227. 
Amygdaline, 469. 
Amylacetic (cenanthic) acid, 560. 
Amylamine, 533, 538. 
Amyle, C 5 H n , 513. 
acetate, 545. 
valerianate, 545. 
Amylene, 509. 
Amylene-glycol, 553. 
Amylethylic ether, 517. 
Amylic alcohol, C 5 H 12 0, 505. 
Amylic iodide, 513. 
Analysis of gaseous hydrocarbons, 106. 
of marsh-gas, 106. 
organic, 80. 

calculation of, 81. 
Anata.se, 385. 



Ancaster stone, 408. 
Anchoic acid, 571. 
Angelic acid, 567. 
Anglesite, PbO.S0 3 , 357. 
Anhydride, acetic, 556. 

benzoacetic, 557. 
benzoic, 470. 
carbonic, 83. 
lactic, 600. 
nitric, 135. 
phosphoric, 232. 
sulphuric, 210. 
sulphurous, 202. 
tartaric, 577. 
Anhydrides of organic acids, 556. 
Anhydrous, 22. 
Anhydrous acids, 42. 
Aniline, C 6 H 7 N, 450. 
black, 453. 
blue, 453. 

constitution, 538. 
colours, 451. 
constitution, 530. 
-green, 453. 
-purple, 451. 
-red, 451. 

constitution, 537. 
salts, 453. 
test for, 451. 
-violet, 453. 

constitution, 538 
-yellow, 452. 
Animal charcoal, 65. 

chemistry, 598. 
heat, 623.' 
Animals, and plants, reciprocity of, 625. 
changes after death, 625. 
destructive functions of, 620. 
nutrition of, 620. 
oxidising functions of, 618. 
ultimate elements of, 620. 
Animi resin, 467. 
Aniseed, essential oil of, 471, 550. 
Anisic acid, 471, 550. 

alcohol, 550. 
Anisyle hydride, 471, 550. 
Annatto, 591. 

Ansell's fire-damp indicator, 95. 
Anthracite, 68. 

composition, 68, 429. 
production of flame from, 85. 
Antichlore, 201, 213. 
Anticorrosive caps, 163. 
Antimonic acid, Sb 2 5 , 375. 
Antimonietted hydrogen, 376. 
Antimony, Sb, 373. 

action on water, 12. 

amorphous, 374. 

antimoniate of teroxide, Sb 2 3 , 

Sb 2 5 375. 
butter of, 376. 
chlorosulphide, 377. 
crocus, 374. 
crude, Sb 2 S 3 , 374. 
detected, 197, 376. 
extraction in the laboratory, 374 
glass of, 377. 
grey ore of, Sb 2 S 3 , 377. 
ore, red, Sb 2 3 .2Sb 2 S 3 , 377. 

white, Sb 2 0„ 375. 
oxide, Sb 2 3 , 375. 
oxychloride, 377. 



632 



INDEX. 



Antimony, oxysulphide, 377. 

pentachloride, SbCl 5 , 377. 
pentasulphide, Sb 2 S 5 , 377. 
potassio-tartrate, 577. 
regulus, 374. 
sulphide identified, 377. 
sulphides, 377. 
terchloride, SbCl 3 , 377. 
teroxide, Sb 2 3 , 375. 
tersulphide, 377. 
tested for lead and iron, 378. 
uses, 374. 

vermilion, 214, 377. 
Antiseptic properties of carbolic acid, 456. 
kresylic acid, 457. 
sulphurous acid, 201. 
Ants, acid of, 557. 

oil of, 558. 
Apatite, 223. 
Apocrenic acid, 619. 
Apple-oil, 545. 

Aq., water of crystallisation, 41. 
Aqua fortis, 131. 
regia, 171. 
Arabine, 477. 

Arachidic (butic) acid, 507. 
Arbor Dianae, 366. 
Archil, 593. 
Argand lamp, 103. 
Argent-acetyle, chloride of, 91. 

oxide of, 91. 
Argent-allylene, 475. 
Argillaceous iron ores, 299. 
Argol, 257, 576. 
Arrack, 504. 

Arragonite, CaO.C0 2 , 277. 
Arrowroot, 480. 
Arsenites, 245. 

normal ratio of, 253. 
Arsenic, As, 239. 

bisulphide, 248. 

combining volume, 239. 

detection, 246. 

extraction, 240. 

extraction from organic matters, 247 

in copper, 338. 

native, 240. 

oxides, 241. 

pentasulphide, 249. 

subsulphide, 248. 

sulphides, 248. 

terbromide, 247. 

terchloride, 247. 

terfluoride, 248. 

teriodide, 247. 

tersulphide, 248. 

identified, 249. 
triethoxide, 528. 
white, 241. 
Arsenic acid, As ? 5 , 244. 

action of hydros ulphuric acid 
on, 249. 
Arsenical nickel, NiAs 2 328. 

paper-hangings, 244. 
pyrites, 240. 
soap, 244. 
Arsenic eating, 244. 
Arsenides, 240. 
Arsenietted hydrogen, AsH 3 , 245. 

decomposed by heat, 246. 
Arsenio-diethyle, 525. 
-dinjethyle, 525. 



Arsenio-sulphides, 240. 
-triethyle, 525. 
-trimethyle, 525. 
Arsenious acid, As 2 3 , 241. 

action of ammonia on, 243. 
chlorine on, 247. 
hydrochloric acid 

on, 247. 
hydrosulphuric acid 
on, 248. 
behaviour with water, 242. 
composition, 241. 
crystalline, 242. 
identified, 241. 
opaque, 242. 
smallest fatal dose, 242. 
tribasic, 243. 
vitreous, 242. 
Arseniuretted or arsenietted hydrogen, 245. 
As, arsenic, 239. 
Asafoetida, 475. 

essential oil of, 474. 
Asbestos, 279. 

AsH 3 , arsenietted hydrogen, 245. 
Ashes of coal, 68. 
As 2 3 , arsenious acid, 241. 
As 2 5 , arsenic acid, 244. 
Asparagine, 580. 
Asparagus, 495. 
Aspartic acid, 580. 
Assay of gold by cupellation, 399. 
Atacamite, 344. 
Atmolysis, 19. 

Atmosphere, composition, 54, 
Atmospheric air, 54. 
Atmospheric germs of putrefaction, 626. 
Atom, definition, 8. 

etymology, 8. 
Atomic formulae, types of, 157. 
Atoinic heat, definition, 9. 

of magnesium, 284. 
Atomic heats, 9. 

of compound bodies, 283. 
oxygen, hydrogen, and 

nitrogen, 9. 
potassium, sodium, and 
lithium, 283. 
Atomicities, classification by, 250. 
Atomicity, 157. 

importance in theory, 250. 
notation of, 250. 
Atomic theory, 8. 
weight, 8. 

of sulphur, 194. 
Atropine, 529. 

Attraction, chemical, definition, 1. 
Au, gold, 396. 

AuCl 3 , terchloride of gold, 401. 
Augite, 290. 
Auric acid, Au 2 3 , 401. 
Autogenous soldering, 205. 
Azobenzide, 450. 
Azolitmine, 594. 
Azote, etymology, 119. 

B, BORON, 116. 

Ba, barium, 274. 

BaCl 2 , chloride of barium, 276. 

Balenic acid, 507. 

Balloons, 14. 

made, 502. 
Balsam of Peru, 466. 



INDEX. 



633 



Balsam of Tolu, 466. 

Balsams, 466. 

Banca tin, 380. 

BaO, baryta, 275. 

BaO.C0 2 , carbonate of baryta, 275. 

BaO.N 2 5 . nitrate of baryta, 275. 

BaO.S0 3 , sulphate of baryta, 275. 

Barilla, 262. 

Bar-iron, best, 311. 

composition, 311. 

crystalline, 313. 

fibrous, 313. 

manufacture, 307. 
Barium, Ba, 274. 

action on water, 11. 

binoxide, 276. 

chloride, BaCJ 2 , 276. 

equivalent and atomic weights, 284. 

sulphide, 275. 
Barlev sugar, 494. 
Baryta, BaO, 275. 

carbonate, 275. 

preparation from heavy 
spar, 275. 

chlorate, 276. 

hydrate, BaO.H 2 0, 275. 

hypophosphite, 235. 

in glass, 404. 

nitrate, BaO.N 2 5 , 275. 

sulphate, 275. 

decomposition, 275. 

sulphovinate, 516. 
Barytocalcite, 277. 
Basalt, 290. 
Base, definition, 26. 
Basicity of acids determined, 255. 
Basic oxides, 26. 
Bassorine, 478. 
Basylous, 249. 
Bathgate coal, 463. 
Bath stone, 408. 
Baths, photographic, recovery of silver from, 

363. 
Battery, galvanic, 4. 
Baume's flux, 412. 

Bauxite, extraction of aluminum from, 288. 
Baysalt, 262. 
Beans, inosite in, 607. 
Bear, 388. 
Beef-tea, 607. 
Beehive-shelf, 11. 
Beer, composition, 486. 
ropy, 487. 
sparkling, 77. 
Bees' wax, 573. 
Bell-metal, 340, 382. 
Bengal saltjoetre, KN0 3 , 409. 
Benic acid, 507. 
Benzamide, 541. 
Benzoacetic anhydride, 557. 
Benzoic acid, HC 7 H 5 2 , 468. 

in cow's urine, 613. 
alcohol, 471, 550. 
anhydride, 470. 
peroxide, 557. 
Benzoin, gum, 468. 
Benzoine, 470. 
Benzole or benzine, C 6 H 6 , 450. 

action of nitric acid on, 134. 

chloride of, 450. 
Benzoline, 558. 
Benzolised air, 105. 



Benzone, 550. 
Benzonitrile, 541. 
Benzophenone, 550. 
Benzoyle, C 7 H 5 0, 470. 

compounds, 470. 

glycocoll, 613. 

hydride, 470. 

peroxide, 557. 

salicylamide, 542. 

salicyle, 472. 

series, 470. 
Benzoyle-urea, 611. 
Benzureide, 611. 
Benzylamine, 550. 
Benzyle, chloride, 550. 
Bergamotte, essential oil of, 465. 
Beryl, 291. 

Bessemer's process (iron), 312. 
Bezoars, 583. 
Bi, bismuth, 371. 
Bibasic acids, constitution, 255. 
Biborate of soda, 266. 
Bibromosuccinic acid, 578. 
Bicarbonate of lime, 45. 

soda, Na 2 O.H 2 0.2C0 2 , 265. 
Bicarbonates, 82. 
Bichloracetic acid, 555. 
Bi-equivalent elements, 158. 
Bile, 622. 
Bimetantimoniate of potash, 375. 

soda, 375. 
Binary formulae, 42. 

theory of acids, 253. 
salts, 253. 
Binoxide of hydrogen, 51. 

■ nitrogen, 137. 
Bi 2 3 , bismuthic oxide, 372. 
Birch, essential oil of, 465. 
Bi 2 S 3 , bismuthic sulphide, 373. 
Biscuit porcelain, 406. 
Bismuth, Bi, 371. 

action on water, 12. 

glance, 373. 

impurities, 372. 

nitrate, Bi 2 3 .3N 2 5 , 373. 

ochre, 373. 

.oxides, 372. 

oxychloride, 373. 

sulphide, 373. 

telluride, 222. 

terchloride, BiCl 3 , 373. 

trisnitrate, 373. 
Bismuthic acid, 373. 
Bistearine, 565. 

Bisulphate of potash, K 2 O.H 2 0.2S0 3 , 130. 
Bisulphide of carbon in coal-gas, 219. 
Bisulphites, 201. 
Bisulphuret of carbon, 216. 
Bitter almond oil, C 7 H B 0, 468. 
Bittern, 172, 262. 
Bituminous coal, 68. 
Bixine, 591. 
Black ash, 263. 

liquor, treatment, 265. 
Blackband, 299. 
Black dyes, 597. 
Blacking, vitriol in, 208. 
Black lead, 60. 

crucibles, 61. 
vitriol, 343. 
wash, 370. 
Blast-furnace, 302. 



634 



INDEX. 



Blast-furnace, chemical changes in, 302. 

gases, 303. 
Blasting with gunpowder, 423. 
Bleaching by chloride of lime, 151. 
chlorine, 151. 
ozone, 53. 

sulphurous acid, 200. 
powder, 151. 
Bleach killed, 201. 
Blende, ZnS, 293. 
Blistered steel, 315. 
Block tin, 380. 
Blood, 603. 

action of oxygen on, 604. 
aeration of, 604. 
coagulation of, 603. 
defibrinated, 603. 
formation from food, 620, 623. 
globules, 603. 
venous and arterial, 604. 
Bloom (iron), 310. 
Bloomery forge, 319. 
Blowers in coal-mines, 95. 
Blowpipe, cupellation with, 352. 
flame, 105. 
hot-blast, 106. 
oxy-hydrogen, 37. 
reduction of metals by, 106. 
table, 113. 
test for lithium, 272. 

potassium, 260. 
sodium, 266. 
Blue bricks, 407. 
copperas, 342. 
dyes, 597. 

fire composition, 164. 
flowers, colouring matter of, 591. 
malachite, 333. 
metal (copper), 337. 
oxide of molybdenum, 387. 

tungsten, 386. 
pill, 365. 
pots, 61. 

Prussian, Fe 4 Fcy 3 , 432. 
stone, 342. 
Thenard's, 328. 
Turnbull's, 438. 
verditer, 343. 
vitriol, 342. 

water of copper mines, 337. 
writing paper, 291. 
B 2 3 , boracic acid, 116. 
Bodies of animals, putrefaction of, 625. 
Boghead cannel, 463. 
Boiler fluid, arsenical, 244. 

incrustations, 45. 
Boiling meat, 607. 
Boiling point, definition, 51. 
Boiling points of benzole series, 445. 
Boiling process (iron), 312. 
Bolsover stone, 408. 
Bone-ash, 223. 

as manure, 616. 
black, 65. 

earth, as manure, 616 
formation from food, 620. 
Bones, ammonia furnished by, 538. 
as manure, 616. 
composition, 223. 
destructive distillation, 65. 
Boracic acid, B 2 3 , 116. 

crystals, 117. 



Boracic acid, 116. 

identified, 117. 
in glass, 404. 
manufacture, 116. 
tribasic, 118. 
vitreous, 117. 
anhydride, 117. 
ether, 515. 
lagunes, 116. 
Boracite, 281. 
Borates, 117. 

normal ratio of, 253. 
Borax, Na 2 0.2B 2 3 , 116, 266. 
glass, 267. 
identified, 267. 
manufacture, 266. 
refining, 266. 
uses, 267. 
vitrefied, 267. 
Boric ethide, 526. 

methide, 526. ' 
Borneene, 466. 
Borneo camphor, 466. 
Borofluoric acid, 186. 
Borofluorides, 186. 
Boron, B, 116. 

amorphous, 118. 
chloride, BC1 3 , 170. 
crystallised, 118. 
diamond, 118. 
fluoride, BF 3 , 186. 
graphitoid, 118. 
nitride, 118. 
terchloride, 170. 
terfluoride, 186. 
Botany Bay gum, 456. 
Boucherie's process for preserving wood, 620. 
Bouquet of wines, 504. 
Boyle's fuming liquor, 271. 
Br, bromine, 172. 
Brandy, 504. 
Brass, 340. 

for engraving, 340. 
guns, 381. 
preparation, 340. 
Brassic acid, 567. 
Braunite, Mn 2 3 , 324. 
Brazil wood, 592. 
Bread, 488. 

aerated, 489. 
new and stale, 489. 
Brewing, 484. 
Bricks, 407. 

efflorescence on, 268. 
Bright iron, 306. 
Brimstone, 189. 
Britannia metal, 381. 
British brandy, 504. 

gum, 481. 
Brochantite, 343. 
Bromates, 174. 
Bromic acid, 174. 
Bromine, Br, 172. 

action on potash, 173. 
chloride of, 175. 
etymology, 173. 
hydrate, 173. 
identified, 173. 
in waters, 172. 
useful applications, 173. 
with hydrogen, 174. 
Bromoform, 541. 



INDEX. 



635 



Bromosuccinic acid, 578. 
Bronze, 340, 382. 

annealing of, 382. 
coin, 382. 
powder, 385. 
Bronzing, 341. 
Brookite, 385. 

Brown acid (sulphuric), 207. 
blaze, 297. 
coal, 67. 
dyes, 597. 
haematite, 300. 
Brucine, 529. 
Brucite, 281. 
Brunolic acid, 445. 
Brunswick green, 344. 
Bubbles, explosive, 32. 
Buckskin, 582. 
Bug-poison, 368. 
Building-materials, 407. 

stone, effect of air of towns on, 408. 
preservation of, 408. 
Bullets, rifle, 353. 

shrapnel, 353. 
Burner, air-gas, 103. 

Bunsen's, 103. 
gauze, 104. 
hot-air, 103. 
ring, 50. 
rosette, 50. 
Burners, smokeless, 103. 
Burnett's disinfecting fluid, 297. 
Burnt iron, 313. 
Butic acid, 507, 572. 
Butine, 572. 
Butter, 572. 
Butter-milk, 599. 

preparation of, 599. 
Butylactic acid, 552. 
Butylamiue, 538. 
Butyle, C 4 H 9 , 513. 
-amyle, 513. 
-caproyle, 513. 
-sulphocyanide, 475. 
Butylene, 509. 

-glycol, 553. 
Butylic alcohol, 505. 
Butyramide, 541. 
Butyric acid, HC 4 H 7 2 , 507, 558. 

formed from citric, 580. 
synthesis of, 559. 
two rational formulae of, 560. 
ether, 545. 
Butyrine, 572. 
Butyrone, 548. 
Butyryle, 548. 

-urea, 612. 

C, carbon, 58. 

Ca, calcium, 277. 

Cacao-butter, 588. 

CaCl 2 , chloride of calcium, 279. 

Cadet's fuming liquor 521. 

Cadmia, CdS, 297. 

Cadmium, Cd, 297. 

carbonate, 297. 

identified, 297. 

iodide, 297. 

oxide, 297. 

sulphide, CdS, 297, 

vapour density, 297. 
C?esia, 274. 



Csesia, carbonate, 274. 
Ceesium, 273. 

platinochloride, 392. 
Caen-stone, 408. 
CaF 2 fluoride of calcium, 181. 
Caffeic acid, 587. 
Caffeine, C 8 H 10 N 4 O 2 , 529. 

chemical constitution, 589. 

extraction of, 588. 

formed from theobromine, 589. 
Caffeone, 587. 
Cairngorm stones, 109. 
Coking-coal, 68. 
Calamine, ZnO.C0 2 , 293. 

electric, 293. 
Calcareous waters, 45. 
Calcium, Ca, 277. 
Calcium, action on water, 11. 

bisulphide, 198. 
• chloride, CaCl 2 , 279. 

equivalent and atomic weights, 284. 

fluoride, CaF 2 , 181. 

oxychloride, 151, 279. 

pentasulphide, 198. 

phosphide, 237. 

sulphide, 264. 
Calc-spar, 277. 
Calculation of formulae, 127. 
Calico-printing, 597. 
Calomel, HgCl, 369. 
Calorific intensity, 426. 
Cameos, 109. 

Camomile, essential oil of, 465. 
Camphilene, 464. 
Camphme, 104, 464. 
Canipholic. acid, 567. 
Camphor, C 10 H 16 O, 466. 
artificial, 464. 
oil of, 466. 
Camphors, 466. 
Camphorimide, 542. 
Candle, chemistry of, 100. 
Candles, 564. 

composite, 564, 567. 
Cane-sugar, C 12 H 22 O n , 492. 

action of yeast on, 485. 
composition, 494. 
Cannel gas, composition, 108. 
CaO, lime, 277. 

CaO.C0 2 , carbonate of lime, 277. 
CaO. O, oxalate of lime, 575. 
CaO.SOg, sulphate of lime, 278. 
Caoutchine, 476. 
Caoutchouc, 475. 

artificial, 572. 
in plant juices, 477. 
solvents for, 476. 
Cap composition, 441. 
Capric (rutic) acid, 507. 
Caprine, 572. 
Caproic acid, 507. 

alcohol, 505. 
Caproine, 572. 
Caproyle, C 6 H 13 , 513. 
Caproylene, 508. 
Caprylene, 508. 
Caprylic acid, 507. 

alcohol, 505, 572. 
Capsicine, 529. 
Caramel, 494. 
Carbazotic acid, 456. 
Carbolic acid, C^H^O, 455 



636 



INDEX. 



Carbolic acid, antiseptic character, 626. 

tests of purity, 455. 
Carbon, C, 58. 

and hydrogen, 88. 

oxygen, 24. 
atomicity, 158. 
atomic weight, 88. 
bichloride, CC1 4 , 168. 
chemical relations of, 65. 
chlorides of, 167. 
circulation in nature, 69. 
determination of, 80. 
natural sources, 58. 
oxides of, 68. 
physical properties, 63. 
sesquichloride, C 2 C1 6 , 167. 
subchloride, C 2 C1 2 , 168. 
use in metallurgy, 66. 
Carbonate of baryta and lime, 277. 
lime and soda, 277. 
lime in waters, 45. 

natural sources of, 70. 
Carbonates, 82. 

additive formulae, 83. 
alkaline, 274. 
normal, 253. 

substitutive formulas, 83. 
Carbon, bisulphide, CS 2 , 216. 
uses, 218. 
burnt to carbonic oxide, calorific 

value of, 429. 
calorific intensity calculated, 426. 
calorific value, 66, 425. 
chlorides, composition by volume, 

169. 
group of elements, 118, 250. 
iodide, 180. 

liquid sesquichloride, CC1 3 , 169. 
oxychloride, COCl 2 , 169. 
oxysulphide, 219- 
protochloride, C 2 C1 4 , 168. 
Carbonic acid, C0 2 , 69. 

absorption by water, 76. 
analysis of, 84. 
composition by volume, 87. 
decomposed by carbon, 84. 

potassium, 84. 
determination of, 80. 
evolved by plants, 69. 
experiments with, 71. 
formation of propylic acid 

from, 525. 
formed in combustion, 69. 
respiration, 69. 
in air, sources of, 69. 
in breathed air, 74. 
injurious effects of, 73. 
liquefaction of, 79. 
preparation, 70. 
properties, 71. 
salts of, 82. 
separation from other gases, 

80. 
springs, 70. 
synthesis of, 58. 
Carbonic anhydride, 83. 

ether, 516. 
Carbonic oxide, CO, 84. 

absorption by cuprous chlo- 
ride, 251. 
action on heated metallic 
oxides, 87. 



Carbonic oxide, calorific value, 429. 

composition by volume, 87. 
decomposition by heat, 87. 
formation in fires, 84. 
formed from steam, 85. 
identified, 84. 

loss of heat in furnaces pro- 
ducing, 429. 
metallurgic applications, 85. 
poisonous properties, 85. 
preparation from carbonic 

acid, 84. 
preparation from ferrocy- 

anide of potassium, 86. 
preparation from oxalic acid, 

86. 
properties, 86. 
Carbonisation, 58. 
Carbonising fermentation, 66. 
Carbotriamine, 537. 
Carbovinate of potash, 516. 
Carburetted hydrogen, 94. 
Carmine, 595. 
Carmine lake, 595. 
Carminic acid, 595. 
Camallite, 260. 
Carnelian, 109. 

Carraway, essential oil of, 465. 
Carre's freezing apparatus, 123. 
Carthamine, 591. 
Cartilage, 608. 
Case-hardening, 317. 
Caseine, 601. 

vegetable, 488, 601. 
Cassia, essential oil, 471. 
Cassiterite, Sn0 2 , 383. 
Cast-iron, composition of, 305. 
for ordnance, 307. 
fusing point, 307. 
grey, 306. 
malleable, 317. 
mottled, 306. 
phosphorus in, 305. 
silicon in, 114. 
specific gravity, 307. 
sulphur in, 305. 
varieties of, 306. 
white, 306. 
Castor oil, 572. 

cold-drawn, 572. 
Cast steel, 316. 
Catalan process, 318. 
Catalysis, 52, 518. 
Catechu, 584. 
Cat's eye, 109. 
Caustic alkali, 11. 

etymology of, II. 
lunar, AgN0 3 , 362. 
potash, 258. 
soda, 265. 
Cd, cadmium, 297. 
Cedar-wood, essential oil, 466. 
Cedrene, 466. 
Cedriret, 460, 463. 
Celery, 495. 

Celestine, SrO.S0 3 , 276. 
Cellulose, C 6 H 10 O 5 , 459. 

converted into sugar, 490. 
solvent for, 342. 
Cement for earthenware, 601. 

Keene's and Keating's, 279. 
Portland, 409. 



INDEX. 



637 



Cement, Roman, 409. 
Scott's, 409. 
Cementation, process, 314. 

theory of, 315. 
Centrifugal sugar drainer, 493. 
Cerasine, 478. 
Cerite, 291. 
Cerium, Ce, 291. 

oxalate, 291. 
oxides, 292. 
Ceroleine, 574. 
Cerotene, 508. 
Cerotic acid, 507, 573. 
Cerotine, 573. 
Ceruse, 355. 

Cerylic alcohol, 505, 573. 
Cetine, 573. 
Cetyle, C 16 H 33 , 573. 
series, 573. 
Cetylene, 509. 
Cetylic alcohol, 505. 

ether, 573. 
CH 3 , methyle, 461. 
CH 4 , marsh-gas, 94. 
CH 4 0, methylic alcohol, 461. 
C 2 H 2 , acetylene, 89. 
C 2 H 4 , olefiant gas, 92. 
C.,H 4 C1 2 , Dutch liquid, 92. 
C 2 YL S , ethyle, 512. 
C 4 H 10 O, ether, 510. 
C 2 H 6 0, alcohol, 509. 
C 6 H 5 , phenyle, 454. 
C 6 H 6 , benzole, 450. 
C 6 H-N, aniline, 450. 
C 7 H.A benzoyle, 470. 
C 10 H 8 , naphthaline, 457. 
Chalcedony, 109. 
Chalk, CaO.C0 2 , 277. 

decomposed by sodium, 84. 
in waters, 45. 
precipitated, 163. 
Chalybeate waters, 49, 320. 
Chameleon mineral, 325. 
Champagne, 503. 
Charbon roux, 413. 
Charcoal, absorption of gases by, 63. 

action of steam on, 86. 

alder, composition, 413. 

animal, 65. 

as fuel, 66. 

ash, 414. 

burning, 62. 

combustion of, 66. 

decolorising properties, 64. 

deodorising properties, 63. 

examination, 414. 

for gunpowder, 413. 

oxidised by nitric acid, 132. 

preparation in the laboratory, 424. 

prepared at different tempera- 
tures, 413. 

properties of, 63. 

retort, 62. 

suffocation, 85. 

wood, 61. 
Charring by steam, 413. 
Cheese, 600. 
Cheltenham water, 49. 
Chemical equivalent, definition, 10. 
Chemistry, definition, 1. 
Cheques, prepared paper for. 482. 
Chessylite, 344. 



Chevreul's investigations, 561. 
Chili saltpetre, NaN0 3 , 409. 
Chill-casting, 307. 
Chimney, hot air, for lamps, 103. 
use of, in lamps, 103. 
ventilation by, 74. 
Chimneys on fire extinguished, 200. 
Chinese wax, 573. 
Chlonaphthalise, C 10 C1 8 , 169. 
Chloracetic acid, HC 2 H 2 C10 2 , 555. 
Chloracetene, 549. 
Chloral, C.,HC1 3 0, 544. 
Chloralum, 288. 
Chloranile, 587. 
Chloraniline, 540. 
Chlorate of baryta, 276. 

potash, KC10 3 , 161. 

action of heat on, 164. 
sulphuric acid 
on, 165. 
and sugar inflamed, 166. 
Chlorate of potash burnt in coal-gas, 164. 
preparation, 161. 
preparation of oxygen 
_ from, 30. 
Chlorates, 163. 

normal ratio of, 253. 
Chlorhydrine, 565. 

of glycol, 551. 
Chloric acid, 161. 

hydrated, 163. 
ether, 515. 
peroxide, C10 2 , 165. 
Chloride of aluminum and sodium, 289. 
ammonium, NH 4 C1, 120. 
' calcium tube, 81. 
lime, 151. 

constitution of, 151. 
spontaneous decomposi- 
tion, 161. 
nitrogen, 170. 

prepartion, 171. 
potassium, solubility of, 410. 
soda, 161. 
sodium, 261. 
sulphury le, 201. 
- thionyle, 201. 
Chlorine, CI, 143. 

action on ammonia, 149. 

hydrosulphuric acid, 196. 
leaves, 151. 
sal-ammoniac, 171. 
water, 149. 
and hydrogen, 146. 

exploded by sun- 
light, 147. 
exploded by spark, 
147. 
atomicity of, 158. 
bleaching by, 150. 
chemical relations of, 145. 
disinfecting properties, 152. 
etymology, 145. 
experiments with, 145. 
group of elements, 186, 250. 
hydrate, 145. 
liquefied, 145. 
occurrence in nature, 143. 
oxides, 159. 

composition bv volume, 

167. 
general review, 167. 



638 



INDEX. 



Chlorine, oxidising action, 150. 
peroxide, 165. 
preparation, 144. 
properties, 145. 
taper in, 150. 
water, 145. 
Chlorite, 290. 
Chlorites, 167. 
Chlorobenzole, 450. 
Chlorocarbonic acid, COCl 2 , 169. 

atomic constitution, 
250. 
Chlorochromic acid, 331. 
Chloroform, CHC1 3 , 543. 
Cliloronitric gas, 172. 
Chloronitrous gas, 1 72. 
Chlorophosphamide, 239. 
Chlorophyll, 591. 
Chloropicrine, CC1 3 (N0 2 ), 456. 
Chlorosulphuric acid, 201. 
Chlorous acid, C1 2 3 , 166. 
Chocolate, 588. 
Choke-damp, 74. 
Cholesterine, C 26 H 44 0, 622. 
Cholic acid, 622. 
Choloidic acid, 622. 
Chondrine, 608. 
Chromates, normal ratio of, 253. 

of lead, 330. 

of potash, 330, 
Chrome-alum, 331. 

Chrome-iron-ore, FeO.Cr 9 3 , 321, 329. 
Chrome-yellow, PbO.Cr6 3 , 330. 
Chromic acid, Cr0 3 , 330. 

action of hydrochloric acid 
on, 157. 
Chromium, Cr, 329. 

action on water, 12. 

chlorides, 331. 

oxides, 330. ' 

oxychloride, 332. 

protoxide, 331. 

sesquichloride, 331. 

sesquioxide, Cr 2 3 , 330. 

sesquisulphide, 332. 

sulphate, 331. 

terliuoride, 332. 
Chrysaniline, 452. 
Chrysene, 459. 
Chrysoberyl, 291. 
Chrysocolla, 344. 
Churning, 599. 
Chyle, 623. 
Chyme, 621. 
Cigars, 590. 
Cinchona bark, 585. 
Cinchonine, 529. 

extraction of, 585. 
Cinder, 68. 
Cinder-iron, 304. 
Cinnabar, HgS, 364. 
Cinnameine, 466. 
Cinnamic acid, C 9 H 8 2 , 466. 
Cinnamon, essential oil of, 4-71. 
Cinnamyle, hydride, 471. 
Circulation of blood, chemistry of, 623. 
Cisterns, incrustations in, 46. 
Citric acid, H 3 C 6 H 5 0„ 579. 
CI, chlorine, 143. 

Clark's process for softening water, 43. 
Clay, 285. 
Claying sugar, 493. 



Clay, ironstone, average yield, 303. 
kidney form, 300. 
Clay ironstones, 299. 
C1 2 0, hypochlorous acid, 160. 
C1 2 3 , chlorous acid, 166. 
C1 2 4 , chloric peroxide, 165. 
Clot of blood, 603. 
Cloves, essential oil of, 465. 
CN, cyanogen, 435. 
CO, carbonic oxide, 84. 
C0 2 , carbonic acid, 69. 
C 2 3 , oxalic acid in combination, 575. 
Coal, m. 

ash of, 68. 
Bathgate, 463. 
bituminous, 67. 

composition of, 429. 
Boghead, 463. 
brown, 67. 
caking, 68. 
cannel, 68. 
combustion of, 67. 
composition of, 68. 
distillation of, 107, 443. 
formation of, 66. 
mines, fire-damp of, 95. 
pit, 67. 

products of combustion, 68. 
distillation, 107. 
stone, 68. 
varieties of, 67. 
Welsh, 68. 
Coal-gas, 107. 

composition of, 108. 
manufacture, 444. 

effect on chemistry, 443. 
purification, 445. 

removal of bisulphide of carbon 
from, 219. 
Coal-naphtha, treatment of, 447. 
Coal-tar, 445. 

distillation of, 447. 
dyes from, 451. 
Coarse copper, 337. 
Coarse-metal (copper), CuFeS 2 , 335. 
Cobalt, Co, 327. 

action on water, 12. 
arseniate, 240. 
bloom, 3CoO.As 2 O i; 240. 
chloride, 328. 

commercial oxide, preparation, 327. 
glance, CoAs 2 .CoS 2 , 327. 
oxides, 327. 
phosphate, 328. 
pyrites, Co 2 S 3 , 328. 
separation from nickel, 327. 
sulphides, 328. 
Cocaine, 529. 
Cocculus Indicus, 473. 
Cochineal, 595. 
Coehlearia, oil of, 475. 
Cocinic acid, 507. 
Cocoa, 583. 
Cocoa-nut oil, 570. 
Codeine, 529. 

constitution, 535, 
extraction, 584. 
Cod-liver oil, 572. 
Coffee, composition, 587. 

roasting, 587. 
Coil, induction, 6. 
Coin-bronze, 340. 



INDEX. 



639 



Coke, 68. 

action of steam on, 86. 
composition, 429. 
Colcothar, 203, 321. 
Cold, greatest artificial, 137. 
saturated solution, 39. 
-shortness in iron, 313. 
Collodion balloons made, 502. 

cotton, 501. 
Colophene, 464. 
Coloj)liony, 464. 
Coloured fires, 164. 
Colouring-matters, animal, 595. 

vegetable, 591. 
Columbite, 388. 
Columbium, 388. 
Colza oil, 571. 
Combination by volume, 34. 

definition, 1. 
Combined carbon in cast-iron, 306. 
Combining proportions, 628. 
Combustibles and supporters, reciprocity of, 

37, 102. 
Combustion, acetylene formed in, 89. 
definition, 22. 
formation of carbonic acid in, 

69. 
-furnace, 81. 
in air, definition, 22. 
in confined air, 73. 
in oxygen, 22. 
temperature of, 426. 
Common salt, NaCl, 261. 
Composition and constitution, 462. 
Compound and mixture, distinction, 57. 

definition, 1. 
Compressed gases, 37. 
Concrete, 409. 
Condenser, Liebig's, 50. 
Condurrite, 240. 
Condy's disinfecting fluid, 326. 
Coniine, 529. 

constitution, 535. 
Constitution of salts, 251. 
Converting furnace, 314. 
Converting vessel, Bessemer 's, 312. 
Cooking, 607. 
Copal, 467. 
Copper, Cu, 333. 

acetylide, 90. 

action of nitric acid on, 133. 

on ammonia and air, 342. 
on water, 12. 
alloys of, 340. 
amalgam, 366. 
ammonio-sulphate, 343. 
Anglesea, 337. 
arsenite, 244. 
basic acetate, 555. 

carbonates, 333, 344. 
phosphates, 344. 
best selected, 335. 
blistered, 336. 
chlorides, 344. 
cleaned, 342. 
detected in lead, 352. 
dry, 336. 

effect of impurities on, 338. 
phosphorus on, 338. 
sea-water on, 339. 
electric conductivity of, 338 
electrotype, 338. 



Copper, emerald, 344. 

extraction in laboratory, 337, 
fusing point, 339. 
glance, Cu 2 S, 333. 
hydrated oxide, 342. 
hydride, 235. 
Lake Superior, 338. 
lead in, 337. 
metallurgy of, 333. 
moss, 336. 
native, 333. 
ore, grey, 333. 
red, 333. 



fusion for coarse metal, 334. 
white metal, 335. 
roasting, 333. 

treatment of, for silver, 359. 
overpoled, 337. 
oxide, CuO, 341. . 
oxides, 341. 
oxychloride, 339, 344. 
peacock, 333. 
pentasulphide, 345. 
phosphide, 237, 345. 
poling or toughening, 336. 
precipitated, 90. 
properties of, 339. 
pyrites, CuFeS 2 , 333. 
quadrant-oxide, 342. 
reduced by hydrogen, 37. 
refining, 336. 
rose, 337. 
sand, 333. 

separated from silver, 360. 
silicates, 344. 
smelting, composition of products 

from, 337. 
smelting, summary of, 333. 
smoke, 334. 
Spanish, 338. 
subchloride, Cu 2 Cl 2 , 344. 
suboxide, Cu 2 0, 342. 
subsulphide, Cu.,S, 345. 
sulphate, CuO. SO 3 , 342. 

action of heat on, 212. 
in bread, 490. 
sulphides, 345. 
tinning, 340, 381. 
tough-cake, 337. 
tough-pitch, 336. 
underpoled, 337. 
verdigris, 340. 
vessels for cooking, 339. 
with aluminum. 289. 
Copperas, FeO.SO,, 322. 

blue, 342. 
Coprolite, 223, 231. 
Coquimbite, 322. 
Coral, 277. 
Corn-flour, 481. 
Corpse-light in coal-mines, 98. 
Corrosive sublimate, HgCl 2 , 368. 

antidote to, 368. 
antiseptic properties, 
369. 
Corundum, 287. 
Cotton, 460. 

and wool, separation of, 609. 
dissolved by ammonio-cupric solu- 
tions, 342. 



640 



INDEX. 



Cr, chromium, 329. 

Crackers, detonating, 442. 

Cream, 599. 

Cream of tartar, 257, 576. 

Creasote, 455, 457. 

Crenic acid, 619. 

Cress, essential oil of, 474. 

Cresylic acid, C 7 H 8 0, 457. 

Cr0 3 , chromic acid, 330. 

Cr 2 3 , sesquioxide of chromium, 330. 

Crocus of antimony, 374. 

Crookes' discovery of thallium, 358. 

Cross-stone, 184. 

Crotonic acid, 567. 

Crow-fig, 589. 

Crucibles, 407. 

black lead, 61. 
graphite, 61. 
Cryolite, 266. 
Crystalline lens, 604. 
Crystallisation, 39. 

Crystals from the leaden chambers, 204. 
CS 2 , bisulphide of carbon, 216. 
Cu, copper, 333. 
CuCl 2 , cupi-ic chloride, 344. 
Cu Cl 2 , cuprous chloride, 344. 
Cudbear, 593. 
Cumidine, 534. 
Cuminic acid, HC l0 H n O 2 , 471. 

alcohol, 550. 
Cummin, essential oil, 471. 
Cumyle, 471. 

hydride, 471. 
Cumylene, 537. 

diamine, 537. 
CuO, oxide of copper, 341. 
CuO. S0 3 , sulphate of copper, 342. 
Cupel-furnace, 351. 
Cupellation on the large scale, 351. 
small scale, 352. 
Cupric acid, 342. 

chloride, CuCl 2 , 344. 
oxide, CuO, 341. 
Cupros-acetyle, chloride, 90. 

oxide, 90. 
Cuprous acetylide, preparation, 89. 
chloride, Cu 2 Cl 2 , 344. 

ammoniacal, 344. 
solution, preparation, 90. 
oxide, Cu 2 0, 342. 
Curarine, 589. 
Curcumine, 593. 
Curd of milk, 601. 
Curing animal matters, 626. 
Current, electric, 4. 
CuS, sulphide of copper, 345. 
Cy am elide, 437. 
Cyanic acid, hydrated, 437. 

ether, 531. 
Cyanide of phosphorus, 438. 

potassium, KCN, 435. 

commercial, 436. 
from blast* furnaces, 
436. 
Cyanides of alcohol -radicals, 520. 
Cyanine, 591. 
Cyanogen, CN, 435. 

chlorides, 438. 
compounds, 431. 
preparation, 435. 
solution, metamorphosis of, 435. 
Cyanuric acid, 438, 610. 



Cy 6 Fe, ferrocyanogen, 432. 
Cvlinder-charcoal, 62, 414. 
Cymole, C l0 H u , 460, 466. 

Dadyle, 464. 

hydrochlorate, 464. 
Damaluric acid, 567. 
Daturine, 529. 
Davy-lamp, 97. 

Deacon's chlorine process, 145. 
Dead head, 382. 
Dead oil of coal-tar, 447. 
Decay, 69. 

Decolorising by charcoal, 64. 
Decomposing-cell, 4. 
Decomposition, definition, 1. 
Definition of acid salt, 254. 
alcohol, 506. 
atomic heat, 283. 
basic salt, 254. 
normal salt, 254. 
salt, 253. 
Deflagrating collar, 24. 
spoon, 24. 
Deflagration, 412. 
Dehydration, 42. 
Deliquescence, 42. 
Density, absolute, 417. 
apparent, 417. 
Deodorising by charcoal, 64. 
chlorine, 152. 
Dephlogisticated muriatic acid, 152. 
Derbyshire spar, 181 
Desilverising lead, 349. 
Destructive distillation, definition, 62. 
Detonating tubes, 163. 
Devitrification, 404. 
Dextrine, C 6 H lft O ;5 , 481. 
Dextrotartaric acid, 579. 
Dhil mastic, 355. 
Diacetine, 555. 
Diacid diamines, 536. 
Dialysis, 111. 
Diamines, 536. 

aromatic, 537. 
Diamond, 58. 

ash of, 60. 

combustion of, 59. 

dust, 60. 
glazier's, 60. 
Diamylamine, 533. 
Diaspore, 288. 
Diastase, 483. 
Diathermanous, 217. 
Diatomic elements, 158. 
Diazoamido-benzole, 454. 
Dichloracetic acid, 555. 
Dichloraniline, 540. 
Dichlorhydrine, 565. 
Didymium, Di, 292. 
Diet, regulation of, 624. 
Diethacetic acid, 560. 
ether, 560. 
Diethoxalic acid, 553. 
Diethylamine, NH(C 2 H 5 ) 2 , 532. 
Diethyl-diethylene-diamine, 536. 
Diethylene-diamine, N 2 H 2 (C 2 H 4 ) 2 , 536. 

-diammonium, hydrate of, 536. 

-diethyl-triamine, 537. 

-trialcohol, 554. 

-triamine, 537. 

-triammonium, trichloride, 538. 



INDEX. 



641 



Dietkylzincamine, 543. 
Diffusibility of gases, definition, 15. 
law of, 16. 
measurement of, 17. 
rate of, 16. 
Diffusion-tube, 17. 
Digestion, 621. 

Dimethacetic (butyric) ether, 559. 
Dimethoxalic acid, 553. 
Dimethylamine, 533. 
Dimorphous, 60. 
Dinas fire-bricks, 407. 
Dinitraniline, 540. 
Dinitrobenzole, 134. 
Dinitro-diphenylamine, 534. 
Dicenanthylene-dianiylaniine, 548. 
Dioptase, 344. 
Diphenylamine, 534. 
Diphenyl-benzoylamine, 534. 

-diethylene-diamine, 536. 
-guanidine, 537. 
-urea, 611. 
Diplatinamine, 393. 
Diplatosamine, 392. 

hydrate, 392. 
hydrochlorate, 392. 
sulphate, 392. 
Discharge in calico-printing, 152, 597. 
Disinfectant, MacDougalTs, 456. 
Disinfecting by chloride of lime, 152. 
chlorine, 152. 
ferric chloride, 322. 
manganates, 325. 
Disinfecting fluid, Burnett's, 297. 

Condy's, 326. 
Disintegration of rocks, 77. 
Disodacetic ether, 559. 
Displacement, collection of gas by, 18. 
Dissociation of sal-ammoniac, 270. 

vermilion vapour, 371. 
Distillation, 49. 

definition of, 49. 
destructive, 62. 
dry, 62. 
fractional, 448. 
Distilled sulphur, 189. 

water, 49. 
Dithionic (hyposulphuric) acid, 215. 
Ditoluylamine, 534. 
Dceglic acid, 567. 
Dolo7nite,MgO.Cn0.2C0. 2 , 280. 
Dough, 488. 
Downcast shaft, 75. 
Dryers, 572. 
Drying gases, 42. 

in vacuo, 209. 
oils, 572. 

over oil of vitriol, 209. 
Ductility of copper, 339. 
Dung as manure, 616. 

-substitute, 245, 268. 
Dutch liquid, C 2 H 4 C1 2 , 92. 

action of chlorine on, 167. 
Dutch metal in chlorine, 146. 
Dyad elements, 158. 
Dyeing, 595. 

Earthenware, 407. 
Earths, alkaline, 282. 

proper, 284. 
Ebonite, 476. 
Economico-furnace for lead-smelting, 343. 



Effervescence, 76. 
Efflorescence, 41. 
Eggs, 606. 
Egg shells, 70, 606. 
Elaene, 509. 
Elaidic acid, 564. 
Elaldehyde, 547. 
Elba iron ore, 300. 
Electrical amalgam, 366. 
Electrogilding, 400. 
Electrolysis, definition, 6. 

of hydrochloric acid, 156. 
of water, 4. 
Electro-negative elements, 6. 
Electroplating, 361. 
Electro-positive elements, 6. 
Element, definition, 1. 
Elements, non-metallic, general review, 249. 
Elemi resin, 467. 
Ellagic acid, 583. 
Embolite, 363. 
Emerald, 291. 
Emery, 287. 
Emetics, 577. 
Emetine, 529. 
Empirical formulae, 82. 
Empirical and rational formula?, 462. 
Empyreumatic, 465. 
Emulsine, 469. 
Enamel glass, 405. 
Endosmose, 603. 
English sulphuric acid, 205. 
Epsom salts, 280. 
Equivalent, definition, 10. 
Erbium, 291. 
Erucic acid,- 567. 
Erythric acid, 593. 
Erythrite, 594. 
Esculetine, 473. 
Esculine, 473. 
Essence of almonds, 468. 

turpentine, 464. 
Essential oils containing sulphur, 473. 

extraction of, 465. 
Ethal, C 16 H 34 0, 573. 
Ethalic acid, 573. 
Ether, (C 2 H 5 ) 2 0, 510. 

chemical constitution, 517. 

decomposition by heat, 89. 

water- type view, 518. 
Etherification, continuous, 510. 

theory of, 517. 
Ethers, derivation from alcohols, 507. 

double, 517. 

perfuming and flavouring, 545. 
Ethylamine, NH 2 (C 2 H 5 ), 531, 533. 
Ethylammonia or ethylia, 531. 
Ethylaniline, 534. 
Ethylate of potash, 518. 
soda, 518. 
zinc, 524. 
Ethyl-codyl-ammonium, hydrate of, 535. 
Ethyle, 2 H 5 , 512. 
Ethyle-amyle, 513. 

-butyle, 513. 

cyanide, 520. 

-glucose, 494. 

hydride, 531. 

hypothesis, 514. 

iodide, 512. 

kakodyle, 525. 

orthocarbonate, 516. 

2s 



642 



INDEX. 



Ethyle subcarbonate, 516. 

sulphide, 519. 
Ethylene, C 2 H 4 , 92. 

bibromide, 536. 

diamine, N 2 H 4 (C 2 H 4 ), 536. 

hexethyl-diphosphonium, hydrate 

of, 539. 
oxide, 551. 
Ethylformiate of soda, 558. 
Ethylic alcohol, 509. 
bromide, 511. 
chloride, 511. 
ether, 510. 
iodide, 512. 
Ethyl-inethyl-phenylamine, 534. 
-urea, 611. 
nicotyl- ammonium, hydrate of, 535. 
Ethylo-platammonium, hydrate of, 540. 

toluidine, 534. 
Ethyloxamide, 541. 
Ethyl-urea, 611. 
Euchlorine, 166. 
Eudiometer, Cavendish's, 32. 
etymology, 32. 
siphon, 34. 
Ure's, 34. 
Eudiometric analysis of air, 34. 

marsh-gas, 106. 
Euodic acid, 507. 
Euphorbium, 475. 
Eupione, 463. 
Eupyrion matches, 166. 
Evernic acid, 593. 
Excretion, 623. 

Explosion of hydrogen and oxygen, 31. 
Explosions in coal-mines, 95. 

F, FLUORINE, 181. 
Fagotting, 311. 
Fallowing, 617. 
Fast colours, 595. 
Fats, 570. 

table of, 574. 
Fatty acid series, 507. 
Fatty acids, preparation, 563. 
Fey, ferrocyanogen, 432. 
Fe, iron, 298. 

Fe. 2 Cl 6 , perchloride of iron, 322. • 
Fe 4 Fcy 3 , Prussian blue, 432. 
Feldspar, 285. 

potash-, 290. 
soda-, 290. 
Fennel, essential oil of, 471. 
FeO, protoxide of iron, 320. 
Fe 2 3 , peroxide of iron, 321. 
Fe. } 4 , magnetic oxide of iron, 321. 
Feb. SO3, protosulphate of iron, 322. 
Fermentation, 69. 

acetous, 487. 

alcoholic, 485. 

arrested by sulphurous acid, 

&c, 201. 
production of carbonic acid 

in, 69. 
viscous, 487. 
Ferric acid, 321. 

chloride, 322. 

molecular formula, 323. 
oxide, 321. 
sulphate, 322. 
Ferricum, 323. 
Ferricyanogen (ferridcyanogen), Cy,Fe, 43S. 



Ferrocyanates, 431. 
Ferrocyanic acid, 431. 
Ferrocyanide of potassium, K 4 Cy 6 Fe, 432. 
action of sul- 
phuric acid on, 
86. 
Ferrocyanogen, Cy 6 Fe, 432. 
Ferrosoferric oxide, 321. 
Ferrosum, 323. 
Ferrous oxide, 320. 

sulphate, 322. 
Ferruretted chyazic acid, 431. 
FeS. 2 , iron pyrites, 189. 
Fibrine, blood-, 605. 

extracted from blood, 603. 
muscle-, 606. 
vegetable, 488. 
Fibroine, 609. 
Fibrous bar-iron, 313. 
Filtration, 64. 

Finery-cinder, 2FeO.Si0 2 , 308. 
Fire-bricks, 407. 
Fire-clay, 285. 
Fire-damp, 95. 

conditions of inflammation, 96. 
indicator, 95. 
Fire, white, composition for, 248. 
Fires, blue flame in, 84. 

coloured, 164. 
Fish oils, 563. 
shells, 70. 
Fixing photographic prints, 214. 
Flags, Yorkshire, 407. 
Flake-white, 373. 
Flame, analysis of by siphon, 102. 
blowpipe, 105. 
cause of luminosity in, 99. 
definition of, 99. 

effect of atmospheric pressure on, 104. 
oxygen on, 106. 
wire-gauze on, 97. 
experimental study of, 100. 
extinction by gases, 72. 
extinguished by carbonic acid, 72. 

good conductors, 97. 
gases in, 100. 
nature of, 99. 
oxidising, 105. 
reducing, 105. 
relation of fuel to, 104. 
separation of carbon in, 101. 
structure of, 99. 
supply of air to, 103. 
Flames, simple and compound, 99. 

smoky, 104. 
Flask, to make a three-necked, 102. 
Flesh, 606. 

composition of, 607. 
juice of, 606. 
Flint, 109. 

and steel, 110. 
Flints dissolved, 267. 
Florence flask, 31. ■ 
Floss-hole, 309. 

Flour, proximate analysis of, 488. 
Flowers bleached by sulphurous acid, 200. 
Fluoboric acid, 186. 
Fluorescence, 473, 586. 
Fluoric acid, HF, 181. 
Fluoride of calcium, 181. 

silicon, 184. 
Fluorides, 183. 



INDEX. 



643 



Fluorine, F, 181. 

attempts to isolate, 183. 
Fluor-spar, CaF, 181. 
Flux, Baume's, 412. 

in iron smelting, 303, 301. 
Food, effect of, upon respiration, 624. 
exportation, 625. 
plastic constituents of, 624. 
preservation of, 626. 
respiratory constituents of, 624. 
Forge-iron, 307. 
Formamide, 541. 
Formic acid, HCH0 2 , 507, 557. 
Formonitrile, 541. 
Formulae, additive, 83. 

calculation of, 82. 
empirical and rational, 462. 
substitutive, 83. 
Formylamine, hydriodate of, 435. 
Formyl-diphenyl-diamine, 536. 
Formyle, CH, 544. 

terchloride of, 544. 
Fouling of guns, 423. 
Foundry-iron, 307. 
Fousel-oil, 505. 
Fowler's solution, 244. 
Fractional distillation, 448. 
Frankincense, 475. 
Franklinite, ZnO.Fe 2 3 , 321. 
Free-stone, 407. 
Freezing-apparatus, 123. 

in red-hot crucible, 199. 
mixtures, 124, 135, 270. 
of water, 51. 

with, bisulphide of carbon, 217. 
French chalk, 279. 
Friction-tubes, 163. 

composition for, 163. 
Fructose, C 6 H 12 6 , 491. 
Fruits, ripening of, 619. 
Fuel, calculation of calorific intensity, 426. 
value, 425. 
chemistry of, 425. 
practical applications of, 426. 
Fuels, composition of, 429. 

illuminating, composition of, 104. 
Fuller's earth, 285. 
Fulminic acid, 440. 
Fulminate of mercury, C 2 HgN 2 2 , 439. 

action of hydrochloric 

acid on, 442. 
preparation, 439. 
properties, 440. 
silver, 441. 
Fulminates, chemical constitution, 442. 

double, 442. 
Fulminating gold, 401. 

platinum, 391. 
silver, 362. 
Fumaric acid, 580. 
Fumigating with chlorine, 152. 

sulphurous acid, 201. 
Fuming sulphuric acid, 203. 
Fumitory, 580. 
Funnel-tube, 13. 
Fur in kettles, 44. 
Furfuramide, 558. 
Furfurine, 558. 
Furfurole, C 5 H 4 2 , 558. 
Furnace, charcoal, 114. 

regenerative, 429. 
reverberatory, 309. 



Furnace, Sefstrom's, 320. 
Furnaces, theory of, 426. 

waste of heat in, 429. 
Fused common salt, 115. 
Fusible alloy, 297. 
Fusing-points of fats, 574. 
Fusion, 112. 
Fustic, 592. 
Fuze, Abel's, 346. 

Armstrong percussion, 230. 

Gadolinite, 291. 

Galbanum, 475. 

Galena, PbS, 346. 

Gallic acid, 583. 

Gall-nuts, 581. 

Galvanic battery, 4. 

Galvanised iron, 292. 

Gamboge, 475. 

Gangue, 304. 

Garancine, 592. 

Garlic, essence, artificial production, 474. 

essential oil of, 474. 
Garnet, 290. 
Gas, air vitiated by, 74. 

-burner, Bunsen's rosette, 50. 
ring, 50. 
smokeless, 103. 
-carbon, 446. 
composition of, 108. 
-cylinder, 19. 
-holder, 59. 
valuation of, 103. 
-jar, 24. 

manufacture of, 444. 
Gaseous hydrocarbons, analysis of, 106. 
Gases, diffusion of, 15. 

expansion by heat, 421. 

in waters, 43. 
Gastric juice, 621. 
Gaultheria, oil of, 462. 
Gauze burner, 104. 
Gaylussite, 111. 
Gedge's metal, 340. 
Geic acid, 619. 
Gelatine, 608. 
German silver, 340. 
Germination, 482, 617. 
Geysers, 110. 
Gilding, 400. 

porcelain, 406. 
Gin, 504. 

Gl, glucinum, 291. 
Glass, 403. 

bottle, 404. 

coloured, 404. 

composition of, 403. 

corrosion by hydrofluoric acid, 183. 

crown, 404. 

decolorised, 405. 

etched, 183. 

flint, 404. 

-gall, 404. 

manufacture of, 403. 

of antimony, 377. 

plate, 404. 

plate perforated, 205. 

-pots, 407. 

silvered, 361. 

window, 403. 
Glauberite, 268. 
Glauber's salt, 144. 



644 



INDEX. 



Glaze for earthenware, 40b 
Glazier's diamond, 60. 
Globuline, 604. 
Glonoine, 569. 
Glucic acid, 494. 
Glucina, 291. 

separation from alumina, 291. 
Glucinum, Gl, 291. 
Glucose, C 6 H 14 7 , 482. 
artificial, 490. 
stearic, 568. 
Glucosides, 471. 
Gluco-tartaric acid, 568. 
Glue, 608. 
Gluten, 488. 

varieties of, 489. 
Glutine, 488. 
Glyceric acid, 553. 

alcohol, 566. 
ether, 566. 
Glycerides, 565. 
Glycerine, C 3 H 8 3 , 566. 

converted into glycol, 566. 
extraction of, 565. 
properties, 566. 
soap, 563. 
triatomic, 554. 
Glyceryle, C 3 H 5 , 554. 
Glycocholic acid, 622. 
Glycocoll (glycocine), C 2 H 5 N0 2 , 609. 
Glycogen, 622. 
Glycol, C. 2 H 6 2 , 550. 

acetobutyrate of, 551. 
aldehyde of, 552. 
binacetate of, 550. 
chlorhydrine of, 551. 
converted into alcohol, 554. 
nionacetate of, 551. 
Glycolic acid, HC 2 H 3 3 , 551. 
Glycols, 550. 
Glycyrrhizine, 495. 
Glyoxal, 552. 
Gneiss, 290. 
Gold, Au, 396. 

and sodium, hyposulphite, 401. 

assay by cupellation, 399. 

coin, 399. 

crucible, 401. 

dissolved, 172. 

extracted from old silver, 398. 

extraction, 397. 

fulminating, 401. 

identification of, 133. 

in chlorine, 146. 

lace cleaned, 436. 

treatment of, 399. 
leaf, 400. 
oxides of, 401. 
physical properties, 400. 
protochloride, AuCl, 401. 
refining, 398. 

removal of mercury from, 366. 
ruby, 228, 400. 
separated from silver and copper. 

210. 
standard, 399. 

specific gravity of, 399. 
sulphides of, 402. 
terchloride, AuCl 3 , 401. 
testing, 399. 
thread, 400. 
Goulard's extract, 555. 



Gradational relations of elements, 186, 274, 

282. 
Grains, brewers', 484. 
Granatite, 184. 
Granite, 285. 

disintegration of, 285. 
Granitic rocks, 257. 
Granulated zinc, 13. 
Grape-husks, 503. 
juice, 503. 
sugar, C 6 H 14 ? , 482. 

composition, 494. 
distinguished from cane-sugar, 
490. 
Grapes, colouring matter of, 591. 
Graphite, 58. 

ash of, 61. 
Graphite crucibles, 61. 

in cast-iron, 61, 306. 
uses of, 61. 
Grease removed from clothes, 450. 
Green, arsenical, 244. 

borate of chromium, 331. 
Brunswick, 344. 
chrome, 330. 
colour of plants, 591. 
fire, composition for, 164. 
flame of baryta, 276. 

boracic acid, 117. 
copper, 344. 
thallium, 358. 
malachite, 344. 
mineral, 344. 
Einman's, 328. 
salt of Magnus, 392. 
vitriol, 322. 
Grey copper ore, 333. 
Grey iron, 306. 

nickel ore, 328. 
powder, 365. 
Gristle, 608. 
Grotto del Cane, 71. 
Grough saltpetre, 409. 
Groups of non-metallic elements, 249. 
Grove's battery, 4. 
Guaiacum resin, 467. 
Guanidine, 537. 
Guanite, 281. 
Guano, 612, 616. 
Guelder rose, 560. 
Gum Arabic, 477. 
British, 481. 
Senegal, 478. 
tragacanth, 478. 
Gum-resins, 475. 
Gums, 477. 

Gun-cotton, C 6 H 7 (N0 o ) 3 5 , 495. 
Abel's, 496. 

compared with gunpowder, 500. 
composition, 497. 
equation of explosion, 499. 
in mining, 500. 

Karolyi's experiments on, 498. 
manufacture, 496. 
objections to, 499, 501. 
preparation on the small scale, 

496. 
products of explosion, 498. 
properties, 500. 
pnlp, Abel's, 497. 
reconversion, 497. 
Gud -metal, 340, 381. 



INDEX. 



645 



Gun-paper, 495. 
Gunpowder, 409. 

calculation of force, 420. 

collection of gases from, 418. 

composition, variations in, 
419. 

dusting, 416. 

effect of pressure on explosion 
of, 424. 

equation of explosion, 419. 

examination of, 417. 

facing, 416. 

glazing, 416. 

granulating or corning, 416. 

heat of combustion, 420. 

hygroscopic character, 417. 

incorporation, 415. 

influence of size of grain, 423. 

manufacture, 415. 

mechanical effect, 422. 

preparation in the laboratory, 
424. 

pressing, 416. 

products of explosion, 418. 

sIoav combustion, 
418. 

properties, 417. 

smoke, 423. 

specific heat of products from, 
421. 

temperature of combustion, 
421. 

volume of gas from, 419. 

white, 164. 
Gutta percha, 477. 
Gypsum, 278. 

H, Hydrogen, 12. 
Hsemateine, 592. 
Hsematine, 604. 
Hcematite, broivn, 300. 

red, Fe 2 3 , 299. 
Hsematosine, 604. 
Haematoxyline, 592. 
Hair, 609. 
Hair-dye, 355, 362. 
Halogen, definition of, 26. 
Halogens, general review of, 186. 
Haloid salts, 26, 186. 
Hammer-slag, 310. 
Hard metal, 381. 
Hardness, degrees of, 47. 
permanent, 47. 
temporary, 47. 
Hard water, 44. 
Harrogate water, 49. 
Hartshorn, spirit of, 123. 
Hausmannite, Mn 3 4 , 325. 
HBr, hydrobromic acid, 174. 
HC1, hydrochloric acid, 153. 
HCy, hydrocyanic acid, 433. 
Heat and temperature, 426. 

atomic, 9. 

rays separated from light, 177, 217. 

relation to chemical attraction, 28. 

specific, 9. 
Heath's patent (steel), 316. 
Heating of hayricks, 67. 
Heat of combustion of hydrocarbons, 426, 
Heat-units, 425. 
Eeowy-lead ore, Pb0. 2 , 355. 
spar, BaO.S0 3 , 274, 



Hemihedral crystals, 579. 
Hemming's jet, 97. 
Hepatic waters, 49. 
HF, hydrofluoric acid, 181. 
2HE.SiF 4 , hydrofluo-silicic acid, 185. 
Hg, mercury, 364. 
HgCl 2 , mercuric chloride, 368, 
HgCl, mercurous chloride, 369. 
HgO, mercuric oxide, 367. 
Hg 2 0, mercurous oxide, 367. 
HgO, N 2 5 , mercuric nitrate, 368. 
Hg 2 O.N 2 5 , mercurous nitrate, 367. 
HgS, sulphide of mercury, 370. 
Hg 2 S, mercurous sulphide, 370. 
HI, hydriodic acid, 179. 
Hippuric acid, HC 9 H 8 N0 3 , 613. 

artificial formation, 613. 
extraction from cow's urine, 
613. 
H 2 0, water, 4. 

H 2 2 , peroxide of hydrogen, 51. 
Homogeneous metal, 318. 
Homologous series, 454. 
Honey, 491. 
Hoofs, 609. 
Hops, 484. 

essential oil of, 465. 
Hornblende, 290. 
Horn-lead, 357. 

-silver, 363. 
Horns, 609. 
Horse-chestnut bark, 473. 

-hair inflamed by nitric acid, 134. 
-radish, essential oil of, 473. 
H 2 O.S0 3 , hydrated sulphuric acid, 202. 
Hot blast, theory of, 427. 

blast iron, 303. 

saturated solution, 39. 
H 2 S, hydrosulphuric acid, 194. 
Humic acid, 619. 
Humus, 619. 
Hyacinth, 292. 

Hydrargyrum cum creta, 365. 
Hydrated acids, 42. 

Hydrate of lime', CaO.H 2 0, 42. 

- potash, K 2 O.H 2 0, 42. 
Hydrates, 39. 
Hydraulic cements, 408. 

main, 444. 
Hydrides of alcohol-radicals, 514. 
Hydriodate of potash, 180. 
Hydriodic acid, HI, 179. 

gas, preparation, 179. 
reducing properties, 179. 
solution, preparation, 179. 
ether, 512. 
Hydrohoracite, 281. 
Hydrobromic acid, HBr, 174. 

ether, 511. 
Hydrocarbons, 88. 

heat of combustion of, 426. 
turpentine-series, 465. 
Hydrochloric acid, HC1, 153. 

absorption by water, 154. 
action of heat on, 155. 
action on metallic oxides, 

156. 
action on metals, 155. 

nitric acid, 172. 
plants, 155. 
analysis of, 156. 



646 



INDEX. 



Hydrochloric acid, composition by volume, 
156. 
decomposed by the bat- 
tery, 148, 156. 
from alkali- works, 154. 
gas, preparation of, 153. 
liquid, 155. 
molecular weight, 157. 
properties, 153. 
pure, preparation of, 154. 
synthesis of, 147. 
valuation of, 154. 
yellow, 154. 
Hydrochloric ether, 511. 

gas, dry, preparation, 155. 
Hydrocyanic acid, HCN, 433. 

anhydrous, 434. 
Liebig's test for, 437. 
synthesis, 91. 
ether, 520. 
Hydrocyan-rosaniline, 453. 
Hydroferricyanic acid, H 3 Cy 6 Fe, 438. 
Hydroferrocyanic acid, H 4 Cy 6 Fe, 433. 
Hydrofluoboric acid, 186. 
Hydrofluoric acid, HF, 181. 

action on metals, 182. 
silica, 183. 
Hydrofluo-silicic acid, 2HF.SiF 4 , 185. 

decomposed by heat, 
185. 
Hydrogen, H, 12. 

and arsenic, 245. 
carbon, 88. 
sulphur, 194. 
binoxide, 51. 
calorific intensity calculated, 427. 

value, 20, 425. 
chemical properties, 18. 

relations, 38. 
determination,- in gases, 34. 
displaced by sodium, 11. 
etymology of, 18. 
experiments with, 14. 
flame, 20. 

identification of, 6. 
peroxide, 51. 
persulphide, 198. 
phosphides, 236. 
physical properties, 14. 
poured up through air, 15. 
preparation with iron, 12. 
zinc, 13. 
purification, 37. 
selenietted, 221. 
sulphuretted, 194. 
Hydrogenium, 39. 
Hydrokinone, 586. 
Hydronitroprussic acid, 439. 
Hydroselenic acid, H 2 Se, 221. 
Hydrosulphocarbonic acid, 219. 
Hydrosulphocyanic acid, HCyS, 437. 
Hydrosulphuric acid, H 2 S, 194. 

action on iodine, 179. 
metallic chlorides, 197. 
oxides, 196. 
solutions of metals, 197. 
sulphurous acid, 216. 
disposal of. 195. 
liquefied, 198. 
preparation, 194. 
production in waters, 213. 
solution of, 195. 



Hydrosulphuric acid, test for, 197. 

use in analysis, 197. 
ether 519 
Hydrotelluric acid, H 2 Te, 222. 
Hydroxylamine, NH 3 0, 134, 515. 
Hyoscyamine, 529. 
Hypobromous acid, 174. 
Hypochlorite of lime, CaO.Cl 2 0, 151. 
Hypochlorous acid, C1 2 0, 160. 

action on sal-ammoniac, 
171. 
Hypogeic acid, 567. 
Hyponitric acid, 140. 
Hyponitrous acid, 139. 
Hypophosphites, 235. 
Hypophosphorous acid, 235. 
Hyposulphates, 215. 
Hyposulphindigotic acid, 595. 
Hyposulphite of soda, Na 2 S 2 3 , 213. 

and perchloride of iron, 

216. 
decomposed by acids, 

214. 
decomposed by heat, 215. 
Hyposulphites, 213. 

constitution of, 215. 
Hyprosulphuric (dithionic) acid, 215. 
Hyposulphurous acid, 213. 

formed from sulphur- 
ous acid, 215. 

I, IODINE, 175. 

Ice, 51. 

Iceland spar, CaO.C0 2 , 277. 
Illuminating gas from water, 85. 
Imides, 542. 

constitution of, 542. 
Imidogen, NH, 542. 
Incorporating mill, 415. 
Incrustation on charcoal, 106. 
Incrustations in boilers, 45. 
Indian fire, 248. 
Indican, 594. 
Indifferent oxides, 27. 
Indigo, action of chlorine on, 150. 

blue, C 8 H s NO, 594. 

copper, CuS, 345. 

red, 594. 

reduced, 594. 

vat, preparation, 594. 

white, C 8 H 6 NO, 594. 
Indigotine, 595. 
Indium, 297. 

oxide, 298. 
Induction coil, 6. 

tube, Siemens', 52. 
Ink, 581. 

blue, 432. 
from logwood, 592. 
red, 592. 

stains removed, 160. 
vanadium, 388. - 
Inorganic substances, definition, 3. 
Inosite, C 6 H 12 O fi , 607. 
Instantaneous light, 390. 
Intensity and quantity, electric, 6. 
Introduction, 1. 
Intumescence, 267. 
Iodates, 178. 
Iodic acid, I 2 0,, 178. 
Todide of ethyle, 512. 
nitrogen, 180. 



INDEX. 



647 



Iodide of potassium, 180. 
silver, Agl, 363. 
Iodine, I, 175. 

action on ammonia, 180. 

potash, 176. 
and starch, 177. 
bromides, 180. 
chloride, IC1, 180. 
etymology of, 175. 
extraction from sea-weed, 175. 
identified, 176. 
oxides, 178. 
terchloride, ICL, 180. 
test for, 177. 
tincture of, 177. 
Iodised starch paper, 53. 
Iodoform, 544. 
Iridium, Ir, 395. 

ammoniochloride, 395. 
-black, 395. 
chlorides, 396. 
oxides, 395. 
Iron, Fe, 298. 

action of acids on, 320. 

air of towns on, 292. 
hydrochloric acid on, 156. 
on water, 12. 
amalgam, 366. 
and carbon, 306. 
and oxygen, 26. 

and potassium, ferrocyanide, 433. 
bar-, 311. 

basic persulphate, 203. 
bisulphide, 300. 
black oxide, 321. 
bright, 306. 
burnt in bisulphide of carbon flam* 

218. 
carbonate, 300. 
cast, 305. 

chemical properties, 320. 
chlorides, 322. 
cold short, 313. 
cyanide, FeCN, 433. 
diatomic, 323. 

equivalent and atomic weights, 323. 
extraction in the laboratory, 319. 
ferricyanide, 438. 
fibre in, 313. 
galvanised, 292. 
glance, 300. 
grey, 306. 

group of metals, general review, 332. 
homogeneous, 318. 
in blood, 604. 
in zinc, 295. 
iodide, 180. 

magnetic oxide, Fe 3 4 , 321. 
metallurgy, 300. 
mottled, 306. 
-mould, 320, 581. 
occurrence in nature, 298. 
of antiquity, 318. 
ores, 298. 

British, composition, 299. 
calcining or roasting, 301. 
oxides, 320. 
passive state of, 320. 
perchloride, Fe 2 Cl 6 , 322. 
. peroxide, Fe 2 3 , 321. 
persulphate, Fe 2 3 .3S0 3 , 322, 
phosphates, 322. 



Iron, phosphorus in, 313. 

plates cleansed, 381. 

protochloride, 322. 

proto-sesquioxide, 321. 

proto-sulphate, 322. 

uses, 322. 

protoxide, FeO, 27 > 320. 

prussiate, 432. 

pure, preparation of, 320. 

purification, 307. 

pyrites, FeS 2 , 189, 300. 

pyrophoric, 27, 87. 

red oxide, 321. 

red short, 313. 

refining, 307. 

rust, ammoDia in, 128. 

rusting of, 320. 

sand, 300. 

scales, 310. 

scurf, 407. 

separation from manganese, 326. 

sesquichloride, 322. 

sesquiferrocyanide, 432. 

sesqui-iodide, 181. 

sesquioxide, 27. 

sesquisulphate, 322. 

smelting, English method, 301. 

specular, 300. 

steely, 314. 

sulphate, action of heat on, 212. 

nitric acid on, 138. 

sulphide, preparation, 194. 

sulphuret, 194. 

sulphur in, 313. 

tincture of, 322. 

tinned, 380. 

triatomic, 323. 

useful properties of, 300. 

variation in strength of, 313. 

white, 306. 

wire, composition, 311. 

works of the Pyrenees, 318. 

wrought or bar, composition, 311. 
direct extraction, 318. 
manufacture, 307. 
Iserine, 385. 
Isethionie- acid, 622. 
Isinglass, 608. 
Isocumole, 445. 
Isodimorphism, 375. 

of antimonious oxide and 
arsenious acid, 250. 
Isomerism, 462. 

explanation of, 458. 
Isomorphism, 343. 
Isoprene, 476. 
Isotartaric acid, 577. 
Isoterebenthene, 464. 
Ivory-black, 65. 

Jatropheste, 481. 

Jellies, fruit, 619. 

Jelly, 608. 

Jet for burning gases, 18. 

Jeweller's rouge, 321. 

Juice of sugar-cane, 492. 

Juniper, essential oil of, 465. 

K, potassium, 257. 
Kakodyle, C. 2 H 6 As, 521. 

chemical constitution of, 522. 

chloride, 521. 



648 



INDEX. 



Kakodyle, cyanide, 522. 

oxide, 521. 

series, 521. 
Kakodylic acid, 522. 
Kaolin, 285. 
Kapnomor, 460, 463. 

Karolyi's experiments on gunpowder, 418. 
KC1, chloride of potassium, 260. 
2KCl,PtCl 4 , platinocliloride of potassium, 

392. 
KC10 3 chlorate of potash, 161. 
K 2 C0 3 , carbonate of potash, 257. 
KCy, cyanide of potassium, 435. 
KCyO, cyanate of potash, 437. 
KCyS, sulphocyanide of potassium, 437. 
Kelp, 175. 

Kermes mineral, 378. 
Kernel roasting, 345. 
Ketones, 548. 

K 4 Fcy, ferrocyanide of potassium, 432. 
K 3 Fdcy, ferricyanide of potassium, 437. 
KHCO3, bicarbonate of potash, 260. 
KHO, caustic potash, 258. 
KHSO4, bisulphate of potash, 211. 
KI, iodide of potassium, 180. 
Kid, 582. 

King's yellow, 248. 
Kinic acid, 585. 
Kino, 584. 

Kinone, C 6 H 4 2 , 586. 
Kirschwasser, 504. 
Kish, 61. 
Klumene, 89. 

KMn0 4 , permanganate of potash, 325. 
KNO3, saltpetre or nitre, 409. 
K 2 0, potash, 258. 

K 2 O.Cr0 3 , chromate of potash, 330. 
K 2 0.2Cr6 3 , bichromate of potash, 330. 
Kola nut, '587. 

K 2 O.Sb 2 5 , antimoniate of potash, 375. 
Koumiss, 600. 
Kreasote, 455, 626. 
Kreatine, C 4 H 9 N 3 0. 2 , 606. 

extraction from flesh, 606. 
Kreatinine, C 4 H 7 N 3 0, 606. 
Kresyle, 457. 
Kresylic acid, C 7 H 8 0, 457. 
Krupp's steel, 318. 
Kryolite, Na 3 AlF 6 , 183. 
K 2 S, sulphide of potassium, 260. 
Kupfemickel, NiAs, 328. 
Kyanising wood, 620. 

Lac, 467, 595. 
seed, 467. 
stick, 467. 
Lacquer, 467. 
Lacquering, 341. 
Lactarine, 601. 
Lactic acid, HC 3 H -0 3 , 552, 599. 

converted into butyric, 559. 

propionic, 600. 
preparation, 600. 
anhydride, 600. 
fermentation, 599. 
series of acids, 552 
Lactide, 600. 
Lactine, C 6 H |2 6 , 602. 
Lactometer, 602. 
Lsevotartaric acid, 579 
Lagunes, boracic, 116. 
Lakes, alumina, 288 



Lamp, action explained, 100. 

-black, 61. 

without flame, 390. 
Lanarkite, 357. 
Lantbanium, La, 292. 
Lapis Lazuli, 290. 
Lard, 573. 
Laughing gas. 136. 
Laurel water, 434, 470. 
Laurent's doctrine of substitution, 457. 

nomenclature, 457. 
Laurie acid, 507. 

alcohol, 505. 
Laurite, 395. 
Law of definite proportions, 8. 

multiple proportions, 142. 
Lead, Pb, 346. 

acetate, Pb(C 2 H 3 2 ) 2 , 555. 

action of acids on, 353. 

sulphuric acid on, 207. 
on water, 12, 48. 

amalgam, 366. 

argentiferous, 349. 

basic carbonate, 355. 
chromate, 330. 

binoxide, 355. 

calcining, 348. 

carbonate, native, 357. 

chloride, PbCl. 2 , 357. 

chlorosulphide, 358. 

chromate, PbO.Cr0 3 , 330. 

dichromate, 330. 

extraction in the laboratory, 352. 

fusing point of, 346. 

-glazed earthenware, 407. 

hard, 348. 

hydrated oxide, 354. 

improving process, 348. 

in cider, &c, 353. 

iodide, Pbl 2 , 178, 357. 

malate, 580. 

metallurgic chemistry, 347. 

molybdate, 387. 

ores, 346. 

oxide, use of, in glass, 404. 

oxides, 354. 

oxychloride, 357. 

peroxide, Pb0 2 , 355. 

phosphate, 357. 

plaster, 566. 

protoxide, PbO, 354. 

pyrophorus, 354. 

selenide, 358. 

smelting, 347. 

Spanish, 349. 

specific gravity, 346. 

sulphate, PbO.S0 3 , 346, 357. 

sulphides, 357. 

tartrate, preparation, 354. 

tribasic acetate, 555. 

uses, 352. 

vanadiate, 388. 
Lead-vitriol, PbO.S0 3 , 357. 
Leaden cisterns, danger, 48. 

coffins, corrosion, 353. 
Leadhillite, 357. 
Leather, 581 
Leaven, 489. 

Leaves, formation of, 618. 
Lecanoric acid, 593. 
Leeks, essential oil of, 473. 
Ognmine. fiOl. 



INDEX. 



649 



^emery's volcano, 193. 
Lemons, essential oil of, 465. 
Lepargylic acid, 571. 
Lepidolite, 271. 
Leucaniline, 452. 

triphenylic, 453. 
Lencic acid, HC 6 H u 3 , 552. 
Leucine, C 6 H 13 N0 2 , 617. 
Leucone, 115, 170. 
Li, lithium, 271. 
Libethenite, 344. 

Lichens, colouring matter from, 593. 
Liebig's condenser, 50. 
Life, its extremes meet, 627. 
Light, action on chloride of silver, 214. 

-rays separated from heat, 177, 217. 
Light carburetted hydrogen, 94. 

oil of coal-tar, 447. 
Lignine, 459. 
Lignite, 67. 

composition, 429. 
Lime, CaO, 277. 

action on soils, 616. 

agricultural uses, 616. 

bicarbonate, 45. 

bimalate, 580. 

burning, 277. 

carbonate, CaO.C0 2 , 277. 
in waters, 45. 

fat, 278. 

hydrate, CaO.H 2 0, 278. 

hypochlorite, 151. 

hyposulphite, 198. 

kilns, 278. 

-light, 38. 

lactate, 600.^ 

overburnt, 278. 

oxalate, CaC 2 4 , 575. 

platinate, 391. 

poor, 278. 

purifier, 445. 

-stone, CaO.C0 2 , 277. 

sulphate, CaO.S0 3 , 278. 

superphosphate, 224. 

test for, 576. 

water, 278. 
Linen, 460. 
Linoleic acid, 572. 
Linseed, 478. 

oil, 572. 

boiled, 572. 
Lipic acid, 571. 

Liquation of argentiferous copper, 359. 
Liquor ammonia?, 120. 

sanguinis, composition, 604. 
Liquorice root, 495. 
Litharge, PbO, 354. 
Lithia, 272. 

carbonate, 272. 
-mica, 271. 
phosphate, 272. 
Lithic (uric) acid, 612. 
Lithium, Li, 271. 

blowpipe test for, 272. 
Litmus, 593. 

commercial, 594. 
paper, 22. 
Loadstone, Fe 3 4 , 27, 300. 
Loam, 285. 
Logwood, 592. 

Looking-glasses silvered, 366. 
Lucifer matches, 164. 229. 



Lucifer matches tipped with sulphur, 226. 
Luminosity of flames, 99. 
Lunar caustic, 362. 
Lupuline, 484. 
Luteoline, 592. 
Luting for crucibles, 294. 
iron joints, 193; 

Madder, 592. 

Magenta, 451. 

Magic Lantern, oil for, 466. 

Magnesia, MgO, 279. 

ammonio-phosphate, 281. 
arsenite, 244. 
borate, 281. 
calcined, 281. 
carbonate, 281. 
citrate, 580. 
- hydrate, 281. 
hydraulic, 281. 
medicinal, 281. 
phosphate, 281. 
silicates, 281. 
sulphate, MgO.S0 3 , 280. 
Magnesian limestone, 280. 

for building, 408. 
Magnesite, 279. 
Magnesium, Mg, 279. 

action on water, 11. 
chloride, 115, 282. 

extraction from sea- 
water, 262. 
diatomic, 284. 
equivalent and atomic weights, 

284. 
extraction, 280. 
nitride, 280. 
properties, 280. 
silicide, 115. 
Magnet-fuze composition, 346. 
Magnetic iron ore, Fe^^ 300. 
Magnus' green salt, 392. 
Malachite, 333. 
Malaeic acid, 580. 
Malamide, 580. 
Malic acid, H 2 C 4 H 4 5 , 580. 

"converted into acetic, 580. 

succinic, 580. 
extracted from rhubarb, 580. 
formed from succinic, 578. 
tartaric, 578. 
Malleability of copper, 339. 
Malleable cast iron, 317. 
Malonic acid, 571. 
Malt dust, 483. 

high dried, 486. 
Malting, 482. 
Manganate of potash, 325. 

soda for preparing oxygen, 
29. 
Manganese, Mn, 323. 

action on water, 11. 

alum, 324. 

binoxide, action of sulphuric 

acid on, 211. 
black, 324. 
carbonate, 324. 
chlorides, 326. 
hydrated peroxide, 32 J. 
oxides, 323. 
peroxide, 323. 
protoxide, MnO, 324. 



650 



INDEX. 



Manganese, recovery from chlorine residues 
326. 
red oxide, 324. 
separation from iron, 326. 
sesquioxide, Mn 2 3 , 324. 
spar, MnO.CO.,, 324. 
sulphate, Mn(XS0 3 , 324. 
test for, 325. 
Manganic acid, 325. 
Manganite, Mn 2 3 .H 2 0, 324. 
Manna, 495. 
Mannitane, 568. 
Mannite, C e H u O e , 495. 
glycerides, 568. 
glycerine, 568. 
stearine, 568. 
Mantle of flame, 102. 
Manures, 615. 
Manuring, 615. 
Maraschino, 504. 
Marble, 277. 
Margaric acid, 507, 570. 
Margarine, 563. 
Marine glue, 476. 
Marking-ink, 362. 
Marl, 285. 
Marsh-gas, CH 4 , 94. 

and chlorine, 150. 
composition by volume, 107. 
eudiometric analysis, 106. 
identified, 95. 
preparation, 95. 
series, C«H2n+2, 514. 
Marsh-mallow, 478. 
Marsh's test for arsenic, 246. 
Mascagnine, 269. 
Massicot, PbO, 354. 
Matches, 164. 

eupyrion, 166. 
lucifer, 229. 
safety, 229. 
silent, 229. 
Vesta, 166. 

without phosphorus, 229. 
Matt, 335. 

Matter, definition of, 1. 
Mauve, 451. 
Mauveine, 451. 
Meadow-sweet, oil of, 471. 
Meal powder, 416. 
Meconic acid, H 3 C 7 H0 7 , 585. 
Meerschaum, 279. 
Melaniline, 537. 
Melissene, 505. 
Melissic acid, 507. 

alcohol, 505. 
Melissine, 573. 
Menachanite, 385. 
Mendipite, PbCl 2 .2PbO, 357. 
Menthene, 466. 
Mercaptan, 519. 
Mercaptide of mercury, 520. 
Merchant bar iron, 311. 
Mercuramine, 367. 
Mercuric ethide, Hg (C 2 H. 5 ) 2 , 526. 
iodide, Hgl 2 , 370. 
methide, 526. 
nitrate, HgO.N 2 5 , 368. 
sulphate, HgO.S0 3 , 368. 
Mercurous iodide, Hgl, 370. 

nitrate, Hg 2 O.N 2 6 , 367. 
sulphate, Hg 2 O.S0 3 , 363. 



I Mercury, Hg, 364. 

action of hydrosulphurio acid on, 
196. 

chloride, 369. 
ammoniated oxide, 367. 
bichloride or perchloride, 368. 
black oxide, Hg 2 0, 367. 
chloride, HgCl 2 , 368. 
chlorosulphide, 371. 
cyanide, Hg (CN) 2 , 434. 
extraction from its ores, 364. 
frozen by liquid sulphurous acid, 

199. 
fulminate, HgC 2 N 2 0.„ 439. 
iodide, 177. 
metallurgy of, 364. 
nitrate, HgO.N 2 5 , 368. 
nitric oxide of, 367. 
nitride, 367. 
oxides, 367. 

protochloride, HgCl, 369. 
protonitrate, Hg 2 O.N 2 5 , 367. 
prussiate, 434. 
red oxide, HgO, 367. 
stains removed from gold, 366. 
subsulphide, 370. 
sulphate, 368. 
sulphide, 370. 
uses of, 366. 
volatility of, 366. 
yellow oxide, HgO, 367. 
Metacetone, 549. 
Metacetonic (propylic) acid, 549. 
Metal, definition, 27. 
Metalamides, 542. 
Metaldehyde, 547. 
Metallic oxides, action of hydrochloric acid 

on, 156. 
Metallurgy of copper, 333. 
iron, 300. 
lead, 347. 
tin, 378. 
zinc, 293. 
Metals, action of hydrochloric acid on, 156. 
hydro sulphuric acid on, 

196. 
oxygen-acids on, 132. 
sulphuric acid ou, 209. 
on water, 10. 
burnt in sulphur vapour, 193. 
chemistry of, 257. 
classification of, 10. 
iron group, general review, 332. 
noble, 12. 

of the alkalies, general review, 274. 
of the alkaline earths, 282. 
of the earths proper, 284. 
platinum group, 393. 
relations to oxygen, 25. 
Metal-slag (copper), 336. 
Metameric, 462. 
Metantimonic acid, 375. 
Metaphosphates, normal ratio of, 253. 
Metaphosphoric acid, H 2 O.P 2 5 , 232. 
Metastannic acid, Sn 5 O l0 , 383. 
Metastyrole, 467. 
Metatartaric acid, 577. 
Metaterebenthene, 464. 
Meteoric iron, 298. 
Methyl-acetyle, 549. 
Methylamine, 533, 538. 
Methylaniline, 534. 



INDEX. 



651 



Methylated spirits, 468. 
Methyle, CH 3 , 461. 

-caproyle, 513. 

iodide, 461. 

oxide, 461. 

-phenylamine, 534. 

prepared from acetic anhydride, 

556. 
salicylate, 462. 
series, 462. 
-theobromine, 589. 
-valeryle, 549. 
Methylene, 508. 
Methylethylamine, 533. 
Methylethylamylophenylium, hydrate of, 

534. 
Methyl ethylaniline, 534. 
Methylethylic ether, 519. 
Methylmorphylammonium, hydrate of, 535. 
Methylic acetate, 461. 

alcohol, CH 4 0, 461, 505. 
formiate, 462. 
hydrate, 461. 
Mg, magnesium, 279. 
MgO, magnesia, 280. 
MgO.S0 3 , sulphate of magnesia, 280. 
Mica, 285, 290. 
Microcosmic salt, 233. 
"Tilk, 599. 

adulteration, 602. 
coagulation of, 600. 
composition of, 602. 
Mill-cake, 416. 

furnace, 311. 
Millstone grit, 407. 
Mimotannic acid, 584. 
Mine iron, 304. 
Mineral green, 344. 

silicates, 289. 
waters, 49. 
yellow, 357. 
Mines, ventilation, 75. 
Minium, PbgO^ 355. ; 
Mirbane, essence of, 134. 
Mirrors, manufacture, 366. 
Mispickel, FeS 2 .FeAs, 240J 
Mixture and compound, distinction, 57. 
Mn, manganese, 323. 
Mn0 2 , peroxide of manganese, 323. 
Moire metallique, 382. 
Molasses, 491. 

Molecular formula of water, 36. 
Molecular formulae, 36. 
Molecular volumes of alcohol-radicals, 513. 
defines, 509. 
weight, 36. 
Molecule, definition, 35. 

of a base determined, 128. 
of an acid determined, 82. 
of water, 36. 
Molecules, 36. 
Molybdate of lead, 387. 
Mohjbdena, MoS 2 , 387. 
Molybdenum, Mo, 387. 

bisulphide, 387. 
blue oxide, 387. 
chlorides, 387. 
metallic, 387. 
oxides, 387. - 
sulphides, 387. 
Molybdic acid, Mo0 3 , 387. 

dialysed, 387. . 



Molybdic ochre, 388. 

Monacetine, 555. 

Mona copper, 337. 

Monad elements, 158. 

Monamines, 530. 

Monatomic elements, 158. 

Monkshood, 580. 

Monobasic acids, constitution of, 254. 

Monophosphamide, 239. 

Monostearine, 565. 

Mordants, 596. 

Moringic acid, 567. 

Moritannic acid, 592. 

Morocco leather, 582. 

Morphine, C 17 H 19 N0 3 , 529. 

characters of, 585. 

constitution, 535. 

extraction, 585. 

hydrochlorate, 585. 
Mortar for building, 408. 
Mosaic gold, 385. 
Mountain ash berries, 580. 
Mucic acid, 478. 
Mucilage, 478. 
Mucus, 609. 
Muffle, 352. 

Mulberry calculus, 574. 
Multiple proportions, law of, 142. 
Munclic, FeS 2 , 300. 
Muntz-metal, 339. 
Murexide, 613. 
Muriate of morphia, 585. 
Muriatic acid, 154. 
Muscle formed from food, 620. 
Mushrooms, 495. 
Muslin, uninflammable, 269, 386. 
Mustard, essential oil of, 474. 

artificial production, 474. 
Myricine, 573. 
Myristic acid, 507. 
Myronic acid, 474. 
Myrosine, 474. 
Myrrh, 475. 

N, Nitrogen, 119. 
Na, sodiuim 261. 
NaCl, common salt, 261. 
Nails, 609. 
Na 2 0, soda, 265. 
Na 2 O.B 2 3 , borax, 116, 266. 
Na 2 C0 3 , carbonate of soda, 263. 
NaHO, caustic soda, 265. 
NaHC0 3 , bicarbonate of soda, 265. 
Na 2 HP0 4 , phosphate of soda, 233, 268. 
NaN0 3 , nitrate of soda, 409. 
Na 2 S0 4 , sulphate of soda, 268. 
Na 2 S 2 3 , hyposulphite of soda, 213. 
Naphtha, coal, 447. 

wood, 461. 
Naphthalic acid, 459. 
Naphthaline, C 10 H 8 , 457. 

chlorides, 458. 

chlorine substrhrtion-products 
from, 457. 

nitro - substitution - products 
from, 458. 
Naphthalising, 102. 
Naples yellow, 376. 
Narcotine, 529. 

extraction, 585. 
Nardic acid, 507. 
Negative pole, 5. 



652 



INDEX. 



Nessler's test for ammonia, 370. 
Nettles, acid of, 557. 
Neutralisation, 10. 
Neutrality of constitution, 252. 
NH 3 , ammonia, 119. 
NH 4 , ammonium, 268. 
NH 4 C1, chloride of ammonium or sal- 
ammoniac, 120. 
2NH 4 C1, PtCl 4 , ammonio-chloride of plati- 
num, 389. 
NH 3 ,RC1, sal-ammoniac, 120. 
(NH 4 ) 2 0, oxide of ammonium, 268. 
(NH 4 ) 2 C0 3 , carbonate of ammonia,, 269. 
(NH 4 ) 2 C 2 4 , oxalate of ammonia, 576. 
(NH 4 ) 2 S0 4 , sulphate of ammonia, 269. 
(NH 4 ) 2 S, sulphide of ammonium, 271. 
Ni, nickel, 328. 
Nickel, Ni, 328. 

action on water, 12. 
arsenical, NiAs 2 , 328. 
arsenio- sulphide, 328. 
^<mce,NiAs 2 ,NiS 2 , 328. 
oxides, 328. 
sulphate, 329. 
sulphides, 329. 
Nicotine, C 10 H 14 N 2 , 529. 

constitution, 535. 
extraction, 589. 
properties, 590. 
Nil album, 293. 
Niobic acid, Nb0 2 , 388. 
Niobium, Nb, 388. 
Nipper-tap, 148. 
Nitraniline, 540. 

Nitrate of potash, action of heat on, 140. 
solubility, 410. 
silver prepared from standard 

silver, 362. 
soda, solubility, 410. 
Nitrates, composition, 136. 

decomposition by heat, 135. 
formation in nature, 129. 
normal ratio of, 253. 
oxidising properties, 131. 
Nitre, KN0 3 , 409. 

action on carbon, 412. 
artificial production, 410. • 
cubic, 268. 
examination of, 411. 
-heaps, 410. 
properties, 412. 

purified in the laboratory, 424. 
refining, 411. 

relation to combustion, 412. 
Nitric acid, HN0 3 , 130. 

action on benzole, 134. 
charcoal, 132. 
hydrochloric acid, 172. 
indigo, 132. 
metals, 132. 
organic substances, 134. 
phosphorus, 132. 
sulphurous acid, 204. 
turpentine, 134. 
anhydrous, 135. 
cause of colour, 131. 
decomposed by heat, 131. 
light, 131. 
distillation of, 131. 
formed from air, 129. 

ammonia, 128. 
from batteries, 141. 



Nitric acid, fuming, 131 . 

hydrated, H 2 O.N 2 5 , 130. 
oxidising properties, 132. 
preparation on the large scale, 

130. 
preparation on a small scale, 130. 
properties, 131. 
strongest, preparation, 131. 
test of strength, 131. 
anhydride, 135. 
ether, 515. 
oxide, NO, 137. 

absorbed by sulphuric acid, 207. 
analysis of air by, 137. 
behaviour with hydrogen, 138. 
identified, 137. 
pure, preparation, 138. 
with bisulphide of carbon, 148. 
peroxide, N0 2 , 140. 

composition by volume, 1 43, 
Nitrification, theory of, 128. 
Nitriles, 541. 
Nitrites, 140. 
Nitrobenzoic acid, 614. 
Nitrobenzole, C e H 5 (N0. 2 ), 450. 
preparation, 134. 
Nitrogen, N, 119. 

atomicity of, 158. 
binoxide, 137. 
bromide, 174. 
bulbs, 127. 

chemical relations, 119. 
chloride, 170. 

preparation, 173. 
circulation in nature, 120. 
determination, 127. 
etymology, 56. 
function in air, 58. 
group of elements, 249. 
identification of, 55. 
iodide, 180. 
oxides, 129. 

atomic constitution, 142. 
general review, 142. 
peroxide, 140. 
preparation, 119. 
properties, 56. 
protoxide, 136. 
sulphide, 219. 
Nitrogenised bodies identified, 65. 
Nitroglycerine, 569. 

use in blasting, 569. 
Nitrohippuric acid, 614. 
Nitromannite, 502. 
Nitromuriatic acid, 172. 
Nitrophenisic acid, 456. 
Niti'oprussides, 439. 
Nitrosubstitution products, 134. 
Nitrotoluole, 455. 
Nitrous acid, N 2 3 , 139. 

action on hvdrosulphuric acid, 

196; 
action on organic substances, 

140. 
commercial, 141. 
composition by volume, 143. 
formed from ammonia, 128. 
oxidising and reducing power, 
112. 
ether, 515. 
Nitrous oxide, N 2 0, 136. 

composition by volume, 112. 



INDEX. 



653 



Nitrous oxide identified, 136. 
Nitroxylole, 455. 
N 2 0, nitrous oxide, 136. 
NO, nitric oxide, 137. 
N 2 3 , nitrous acid, 139. 
N0 2 , nitric peroxide, 140. 
N 2 5 , nitric acid, 130. 
Noble metals, 12. 
Non -metallic elements, 1. 
Nordhausen oil of vitriol, 202. 
Normal ratios of salts, 253. 
Normal salt, unitary definition 2 254. 
Normandy's still, 50. 
Nuggets, 397. 
Nutrition of animals, 620. 
plants, 614. 
plastic elements of, 624. 
Nux-vomica, 589. 

O, OXYGEN, 21. 

O, oxalic acid, 574. 
Oak bark, 581. 
Occlusion of hydrogen, 38. 
Ochres, 285. 
CEnanthene, 508. 
CEnanthic acid, 507, 572. 

synthesis, 560. 
alcohol, 505. 
CEnanthole, 572. 

Oil gas absorbed by sulphuric acid, 210. 
Oil of spiraea, 471. 
Oil of vitriol, H 2 O.S0 3 , 202. 
brown, 207. 
dehydrated by phosphoric 

acid, 210. 
dissociation of, 211. 
distillation of, 208. 
manufacture, 203. 
sulphate of lead ;n, 208. 
Oil of wine, 516. 
Oils, 570. 
Olefiant gas, C 2 H 4 , 92. 

absorbed by sulphuric acid, 

210. 
combination with chlorine, 92. 
converted into alcohol, 518. 
decomposed by chlorine, 93. 
heat, 94. 
the spark, 94. 
identification of, 92. 
preparation, 92. 
with iodine, 180. 
Olefines, C»Ha., 508. 
Oleic acid, HC 18 H 33 2 , 571. 

action of nitric acid on, 571 . 
Oleine, C 57 H 104 O 6 , 570. 

synthesis of, 565. 
Olibanum, 475. 
Oligist iron ore, 300. 
Olive-oil, 563, 570. 
Olivine, 281. 
Onions, 495. 

essential oil of, 473. 
Onyx, 109. 
Oolite limestone, 277. 
Oolitic iron ore, 300. 
Opal, 109. 
Opium, composition, 584. 

extraction of alkaloids from, 584. 
Orange chrome, 2PbO.Cr0 3 , 330. 
Orange, essential oil of, 465. 
Orceine, 593. 



Orcine, 593. 

Ore-furnace, 334. 

Organic analysis, elementary, 80. 

and inorganic substances, 430. 
chemistry, 430. 
matter identified, 58. 
substances, definition, 3. 

synthetical formation 
89. 
Organo-metallic bodies, 521. 

table of, 527. 
Oriental alabaster, 47. 
Orpiment, red, As 2 S 2 , 248. 

yellow, As 2 S 3 , 248. 
Orthoclase, 290. 

Orthophosphates, normal ratio of, 253. 
Orthophosphoric acid, 3H 2 O.P 2 6 , 233. 
Osmazome, 608. 
Osmic acid, Os0 4 , 394. 
Osmiridium, 389. 
Osmium, Os, 394. 

chlorides, 395. 
oxides, 395. 
tetrasulphide, 395. 
Osseine, 608. 
Oswego, 481. 
Oxalates, 576. 
Oxalethylic acid, 514. 
Oxalic acid, H 2 C 2 4 , 514. 

analysis of, 81. 
fatal dose, 576. 
occurrence in nature, 574. 
preparation, 574. 
properties, 575. 
test for, 575. 
uses, 574. 
ether, 514. 
Oxalonitrile, 541. 
Oxalovinic acid, 514. 
Oxalyle, C 2 2 , 542. 
Oxamic acid, 541. 
Oxamide, N 2 H 4 .C 2 2 , 540. 
Oxanilide, 541. 
Oxidation, definition, 21. 

of tissue, products, 623. 
Oxide of copper reduced by hydrogen, 37. 
Oxides, 21.- 

metallic, action of hydrochloric acid 
on, 156. 

hydrosulphuric 
acid on, 196. 
sulphuric acid 
on, 211. 
nomenclature of, 27. 
Oxidising blowpipe flame, 105. 
Oxycalcium light, 38. 
Oxygen, O, 21. 

absorption by pyrogallic acid, 583. 

atomicity of, 158. 

blowpipe flame, 106. 

burnt in ammonia, 128. 

combustion in, 22. 

detected in mixed gases, 137. 

determination of, in gases, 33. 

effect on flame, 106. 

electro-negative, 52. 

electro-positive, 52. 

etymology, 24. 

evolved from steam, 149. 

experiments with, 22. 

extracted from air, 28. 

group of elements, 249. 



6D4: 



INDEX. 



Oxygen, identified, 6. 

natural sources, 21. 
preparation, 28. 

from air, 28. 

from bichromate of 

potash, 211. 
from chloride of lime, 

161. 
from sulphate of zinc, 

212. 
from sulphuric acid, 
209. 
properties, 21. 
purification, 58. 
relation to metals, 25. 

non-metals, 22. 
Oxygenated water, 51. 
Oxygenised muriatic acid, 153. 
Oxyhydrogen blowpipe, 37. 
Oxymuriatic acid, 153. 
Ozone, 52. 

electrolytic, 52. 
experiments with, 52. 
in the atmosphere, 51. 
nature of, 52. 
specific gravity of, 53. 
test for, 52. 
Ozonisation by ether, 53. 

phosphorus, 53. 
Ozonised air, 52. 

oxygen, 52. 
Ozonising tube, 52. 

P, phosphorus, 223. 

Paint blackened by hydrosulphuric acid, 197. 

removed from clothes, 450. 
Paintings, effect of light and air on, 197. 
Palladamine, hydrochlorate, 393. 
Palladium, Pd, 393. 

carbide, 394. 
chlorides, 394. 
cyanide, 393. 
nitrate, 394. 

occlusion of hydrogen by, 38. 
oxides, 394. 
Palmitic acid, 507. 
Palmitine, C 5l H 98 0e, 562. 

synthesis of, 565. 
Palm-oil, 562, 570. 

bleaching of, 570. 
Pancreatic juice, 622. 
Panification, 489. 
Papaverine, 529. 
Paper, 460. 

action of nitric acid on, 495. 
dissolved by ammonio-cupric solu- 
tion, 342. 
for cheques, &c, 482. 
for photographic printing, 214. 
Paracyanogen, C 3 N 3 , 435. 
Paraffine, C. r H 2ir + 2 , 462. 
extraction, 462. 
oil, 462. 
Paraguay tea, 587. 
Paramylene, 508. 
Paranaphthaline, 459. 
Paraniline, 537. 
Parasorbic acid , 580. 
Paratartaric acid, 578. 
Parchment, 582. 

size, 609. 
vegetable, 491. 



Paris yellow, 357. 

Parsley, essential oil of, 465. 

Partial saturation, method of, 561. 

Parting of gold by sulphuric acid, 210. 

Passive state of metals, 320. 

Patent yellow, 357. 

Pattinson's process, 350. 

Paviine, 473. 

Paving stones, 407. 

Pb, lead, 346. 

PbCl 2 , chloride of lead, 357. 

Pbljj, iodide of lead, 357. 

PbO, protoxide of lead, 354. 

PbO.Cr0 3 , chromate of lead, 330. 

PbO.S0 3 , sulphate of lead, 346, 357. 

PbS, sulphide of lead, 316. 

Pd, palladium, 393. 

Pea iron ore, 300. 

Pear flavour, 545. 

Pearlash, 257. 

Pearl hardener, 279. 

Pearls, 70. 

Pearl-spar, 281. 

Pearl white, BiCl 3 , BL 2 3 , 373. 

Peas, 601. 

Peat-bog, 67. 

composition, 429. 
Pectic acid, 619. 
Pectine, 619. 
Pectose, 619. 
Pectosic acid, 619. 
Pelargonic acid, 507. 
Pentathionic acid, 216. 
Pentethylene - tetrethyl - tetrammonium, h v 

drate of, 538. 
Pepper, essential oil of, 465. 
Peppermint, essential oil of, 466. 
Pepsine, 621. 
Perchlorates, 165. 
Perchloric acid, 165. 

hydrated, 165. 
ether, 515. 
Perchlorokinone, 587. 
Perchromic acid, 331. 
Percussion cap composition, 441. 

fuze, 166. 
Perfume-ethers, 545. 
Perfumes, extraction of, 465. 
Periclase, 281. 
Pericline, 290. 
Periodates, 178. 
Periodic acid, I 2 7 , 178. 
Permanent gas, 21. 

ink, 362. 

white, 275. 
Permanganate of potash, KMn0 4 , 325. 
Permanganates, normal ratio of, 253. 
Permanganic acid, 325. 
Perspiration of the skin, 559. 
Peruvian bark, 585. 

saltpetre, NaN0 3 , 409. 
Petalite, 271. 
Petinine, 538. 
Petrifying springs, 46. 
Petroleum, 95, 463. 
Peucyle, 464. 
Pewter, 381. 
Phenic acid, 455. 
Phenole, C 6 H 6 0, 455. 
Phenose, 450. 
Phenylamine, 454, 530. 
Pbenylaniline, 534. 



INDEX. 



655 



Pkenyle, C 6 H 5 , 454. 

hydrate, 455. 
Phenylene-diamine, 536. 
Phenylene-ditolylene-triamine, 537. 
Phenylene-ditolylene-triethyl-triamine, 538. 
Phenylene - ditolylene - triphenyl - triamine, 

538. 
Phenylic hydride, 457. 
Phenyl-toluylamine, 534. 
Philosopher's wool, 293. 
Phlogistic theory, 152. 
Phlogiston, 152. 
Phloretine, 473. 
Phloridzeine, 473. 
Phloridzine, 473. 
Phocenine, 573. 
Phosgene gas, COCl 2 , 169. 
Phospham, 239. 
Phosphamic acid, 238. 
Phosphates, normal ratio of, 253. 
Phosphethylic acid, 512, 516. 
Phosphides, 228. 
Phosphites, 234. 
Phosphodiamide, 239. 
Phosphoglyceric acid, 566. 
Phosphomolybdate of ammonia, 387. 
Phosphorescence, 225. 

prevented, 225. 
Phosphoric acid, P 2 5 , 230. 

anhydrous, preparation, 

232. 
bibasic, 232. 
common, 233. 
di-hydrated, 232. 
glacial, 231. 

hydrated, preparation, 231. 
molybdic test for, 387. 
monobasic, 232. 
monohydrated, 231. 
tribasic, 233. 
trihydrated, 233. 
anhydride, 232. 
ether, 516. 
Phosphorised oil, 226. 
Phosphorite, 223. 
Phosphorous acid, P 2 3 , 234. 
Phosphorus, P, 223. 

action of potash on, 236. 

allotropic modifications, 227. 

amorphous, 227. 

and oxygen, 22. 

black, 228 

bromides, 238. 

burnt under water, 166, 235. 

chemical relations, 228. 

chlorides, 237. 

cyanide, 438. 

distilled, 227. 

fuze composition, 229. 

iodides, 238. 

match-bottle, 226. 

occurrence in nature, 223. 

oxides, 230. 

oxychloride, 237. 

pentachloride, 237. 

action of am- 
monia on, 239. 
poisonous properties, 228. 
precipitation of metals by, 228. 
preparation, 223. 
properties, 225. 
red, 227. 



Phosphorus, suboxide, 235. 
sulphides, 238. 
sulphochloride, 238. 
terchloride, 237. 
transformed by iodine, 238. 
viscoixs, 228. 
vitreous, 227. 
Phosphotriamide, 239. 
Phosphovinic acid, 512, 516. 
Phosphurets, 228. 

Phosphuretted hydrogen, gaseous, PH 3 , 236. 
analogy with am- 

amonia, 237. 
composition, 236. 
liquid, 236. 
solid, 238. 
Photographic baths, recovery of silver from, 

363. 
Photographic printing, 214. 
Phthalic acid, 459. 
Phyllocyanine, 591. 
Phylloxanthine, 591. 
Physetoleic acid, 567. 
Picamar, 463. 
Picoline, 445. 
Picric acid, 456. 
Picrotoxine, 473. 
Pig iron, 303. 
Pimelicacid, 571. 
Pimple metal (copper), 337. 
Pine apple flavour, 545. 
Pinic acid, 465. 
Pink salt, 2NH 4 Cl.SnCl 4 , 384. 
Pins tinned, 381. 
Pipe-clay, 285. 
Piperine, 529. 
Pipette, curved, 80. 
Pit charcoal, 414. 
Pitch, 447, 463. 
Pitchblende, 298. 
Pittacal, 463. 

Plants and animals, reciprocity of, 629. 
changes after death, 619. 
chemical changes in, 617. 
constructive power of, 618. 
evolution of carbonic acid bv, 69. 
food^of, 77, 614. 
nutrition of, 614. 
reducing functions of, 618. 
ultimate elements of, 614. 
Plaster of Paris, 278. 

overburnt, 279. 
preparation, 279. 
Platammon-ammonium, hydrated oxide, 540. 
Platammonium, hydrated oxide, 540. 
Platina, muriate, 391. 
Platinamine, 393. 
Platinates, 391. 
Platinised asbestos, 138. 
Platinochloride of potassium, 2KCl.PtCl 4 , 

392. 
Platinoid metals, general review of, 396. 
Platinum, Pt, 388. 

amalgam, 366. 
ammonio-chloride, 2NH,C1. PtCl 4 , 

392. 
and rhodium alloy, 394. 
attacked by sulphuric acid, 209. 
bichloride, PtCl 4 , 391. 
black, 390. 
corroded, 391. 

by arsenites, 243. 



656 



INDEX. 



Platinum, corroded by phosphorus, 228. 
silicon, 114. 
crucible heated, 112. 
extraction, 389. 
fulminating, 391. 
ores, analysis, 396. 
oxides, 391. 

protochloride, PtCl 2 , 392. 
separation from iridium, 391. 
spongy, 389. 

stills for sulphuric acid, 207. 
sulphides, 393. 
uses of, 389. 
Platosamine, hydrate, 393. 

hydrochlorate, 393. 
sulphate, 393. 
Plato-triethyle-arsonium, chloride, 540. 
-phosphonium, 540. 
-stibonium, 540. 
Plumbago, 60. 
Plumbic acid, Pb0 2 , 355. 
Pneumatic trough, 28. 
P 2 3 , phosphorous acid, 234. 
P 2 5 , phosphoric acid, 230. 
Poison-nut, 589. 
Pole, negative, 5. 
positive, 5. 
Pollux, 274. 
Polyammonias, 535. 
Polyatomic alcohols, 550. 
Polyhalite, 281. 

Polymerising by sulphuric acid, 447. 
Polvmerism, 508. 
Populine, 473. 
Porcelain, 405. 

English, 406. 
glazed, 406. 
painting, 406. 
Porous cell experiment, 18. 
Porphyry, 290. 
Porter, composition, 486. 
Portland cement, 409. 

stone, 408. 
Port wine crust, 503. 

effect of keeping, 503. 
Positive pole, 5. 
Potash-albite, 290. 
Potash, K 2 0, 259. 

anhydrous, 259. 

antimoniate, K 2 O.Sb 2 5 , 375. 

arsenite, 244. 

aurate, 401. 

biantimoniate, 375. 

bicarbonate, K 2 O.H 2 0.2C0 2 , 260. 

bichromate, K 2 0.2Cr0 3 , 329. 

bimetantimoniate, 375. 

binoxalate, 576. 

bisulphate, K 2 O.H 2 0.2S0 3 , 130, 

211. 
bitartrate, 258, 576. 
bi-urate, 612. 
bromate, 173. 
bulbs, 81. 

carbonate, K 2 O.C0 2 , 257. 
caustic, 258. 
chlorate, KC10 3 , 161. 
chromate, K. 2 O.Cr0 3 , 330. 
cyanate, KCNO, 437. 
ferrate, 321. 
from wool, 258. 
fulminurate, 443. 
fused, 258. 



Potash, hydrate, KHO, 258. 
hydriodate, 180. 
in flesh, 607. 
iodates, 178. 
isocyanurate, 443. 
manganate, 325. 
metantimoniate, 375. 
metastannate, 383. 
nitrate, 409. 

solubility, 410. 
oleate, 563. 
osmite, 395. 
perchlorate, 165. 
permanganate, 325. 
plumbate, 355. 
prussiate, K 4 Cy 6 Fe, 432. 
quadroxalate, 576. 
red prussiate, 437. 
sulphate, K 2 O.S0 3 , 211. 
tartrate, 2KO. C 8 Et 4 O l0 , 576. 
terchromate, 330. 
test for, 40. 
trithionate, 215. 
urate, 612. 
Potassamide, NH 2 K, 542. 
Potassium, K, 257. 

action on hydrosulphuric acid, 

196. 
action on water, 10. 
alcohol, 518. 
amidide, 542. 
atomic weight, 257. 
bisulphide, 260. 
blowpipe test for, 260. 
bromide, 173. 
chloride, KC1, 260. 

extraction from sea- 
water, 260. 
solubility, 410. 
cyanide, KCN, 435. 
pure, 436. 
equivalent weight, 10. 
ethyle, 525. 
extraction, 259. 
ferricyanide, K 3 Cy 6 Fe, 437. 
ferrocyanide, K 4 Cy 6 Fe, 432. 
heated in carbonic acid, 84. 
iodide, KI, 180. 
mercaptan, 519. 
pentasulphide, 260. 
peroxide, 260. 
platinochloride, 2KCl.PtCl 4 , 

392. 
properties, 259. 
silicofluoride, 185. 
sulpharsenite, 248. 
sulphide, K 2 S, 260. 
sulphocyanide, KCyS, 437. 
tersulphide, 260. 
tetrasulphide, 260. 
Potato, composition, 478. 
spirit, 505. 

starch, extraction, 478. 
Pottery, 405. 
Press cake, 416. 
Pressure of gases, 16. 
Preston salts, 269. 
Promethean light, 166. 
Proof spirit, 509. 
Propione, 548. 

Propionic (propylic) acid, t»07. 
Propionitrile, 541. 



INDEX. 



657 



Propylamine, 538. 
Propylene, 509. 
Propylene-glycol, 553. 
Propylic acid, HC 3 H 5 0. 2 , 507. 

artificial formation, 525. 
alcohol, 506. 
Proteine, 605. 

Proximate organic analysis, 447. 
Prussian blue, Fe 4 Fcy 3 , 432. 

constitution, 433. 
decomposition by alkalies, 

433. 
native, 322. 
preparation, 432. 
soluble, 432. 
Prussiate of potash, action of sulphuric 

acid on, 86. 
Prussic acid, HCy, 431. 

in bitter almond oil, 470. 
of the Pharmacopoeia, 434. 
Psilomelane, 324. 
Pt, platinum, 388. 
PtCl 2 , platinous chloride, 392. 
PtCl 4 , bichloride of platinum, 391. 
Ptyaline, 621. 

Puddled bar, composition, 311. 
bars, 310. 
steel, 318. 
Puddling, disadvantages of, 312. 
dry, 312. 
loss in, 311. 
mechanical, 312. 
process of, 310. 
Pulvis fulminans, 413. 
Pumice stone, 285. 
Purbeck stone, 408. 
Purple of Cassius, 402. 
Putrefaction, 69. 

ammonias furnished by, 538. 
modern researches on, 626. 
Putty powder, 383. 
Pyrene, 459, 460. 
Pyridine, 445. 
Pyrites arsenical, 240. 

capillary, NiS, 329. 
efflorescent, 203. 

extraction of sulphur from, 189. 
Fahlun, 220. 
oxidation in air, 203. 
white, 203. 
Pyrogallic acid, 583. 
Pyrogalline, 583. 
Pyroligneous acid, C„H 4 2 , 460. 

ether, 461. 
Pyrolusite, Mn0 2 , 324. 

preparation of oxygen from, 30. 
Pyromucic acid, 558. 
Pyrophoric iron, 87. 
Pyrophorus, lead, 354. 
Pyrophosphates, normal ratio of, 253. 
Pyrophosphoric acid, 2H 2 O.P 2 5 , 232. 
Pyroterebic acid, 567. 
Pyroxylic spirit, 461. 
Pyroxyline, 495. 

QlJADEEQUIVALENT ELEMENTS, 158. 

Quantity and intensity, electric, 6. 
Quartation of gold, 399. 
Quartz, 109. 

artificial, 112, 516. 
Quercetine, 473. 
Quercitannic acid, 581. 



Quercitrine, 473. 
Quercitron, 597. 
Quick lime, CaO, 42. 
Quicksilver, 364. 
Quince-seed, 478. 
Quinic acid, 586. 
Quinidine, 529. 

extraction, 586. 
Quinine, C 2o H 24 N 2 2 , 529. 

amorphous, 586. 

extraction, 585. 

sulphate, 586. 
Quinoidine, 586. 
Quinoline, 445. 
Quinone, 586. 
Quinotannic acid, 585. 

Racemic acid, 578. 
Radicals, alcohol-, 512. 

polyatomic, 536. 
Radishes, essential oil of, 474. 
Railway bars, 310. 
Rain water, 42. 
Raisins, 491. 
Rancid oils, 571. 
Rangoon tar, 463. 
Rational formulae, 82. 
Ratios, normal, of salts, 253. 
Realgar, As 2 S 2 , 248. 
Reaumur's p"orcelain, 404. 
Reciprocal combustion, 37. 
Red copper ore, Cu 2 0, 333. 
Red dyes, 596. 

fire, composition for, 164. 

flowers, colouring matter of, 591. 

lead, Pb 3 4 , 355. 

-ore, PbO.Cr0 3 , 330. 

ochre, 300. 

orpiment, 248. 

paints, 371. 

precipitate, 367. 

-shortness, 313. 

silver-ore, 3Ag 2 S.As 2 S 3 , 240. 

sulphide of antimony, 377. 
Reduced, 28. 

Reducing blowpipe flame, 105. 
Reduction of metals by carbonic oxide, 87. 

on charcoal, 106. 
Refinery, 308. 
Refining cast-iron, 307. 
Refraction of saltpetre, 409. 
Refrigerator, Carre's, 123. 
Regulus, 335. 
Reguius of antimonv, 374. 
Rennet, 600. 
Resins, 467. 

Resists (calico-printing), 597. 
Respiration, 69. 

formation of carbonic acid in, 69. 
in confined air, 74. 
Retort, 50. 
Rhodium, Ro, 394. 

oxides, 394. 
sesquichloride, 394. 
sodio chloride, 394. 
sulphides, 394. 
Rice, composition, 479. 
Ricinoleic acid, 572. 
Rinman's green, 328. 
Rising of bread, 489. 
Rivers, self- purifying power of, -13. 
River-water, 43 



658 



INDEX. 



Ro, rhodium, 394. 

Boasting, effect on sulphides, 198. 

meat, 608. 
Eochelle salt, KNaC 4 H 4 6 , 578. 
RocJc crystal, 109. 
oil, 463. 
salt, 261. 

disintegration, 77. 
Roman cement, 409. 
Rosaniline, 452. 

acetate, 452. 

action of cyanide of potassium on, 

453. 
triethylic, 453. 
triphenylic, 453. 
Rosette copper, 337. 
Rosiclers, 364. 
Rosin, 464. 

soap, 465. 
Rosolic acid, 445. 
Rotation of crops, 617. 
Rubian, 592. 
Rubidia, 273. 
Rubidium, Rb, 273. 

platinochloride, 392. 
properties, 273. 

separation from potassium, 392. 
Ruby, 287, 330. 
glass, 400. 
Rue, essential oil of, 548. 
Rufigallic acid, 583. 
Ruhmkorff's induction coil, 6. 
Rum, 504. 

Rust, 2Fe 2 3 .3H 2 0, 320. 
ammonia in, 128. 
Rusty deposit in waters, 49. 
Ruthenic acid, 395. 
Ruthenium, Ru, 395. 
Rutic acid, 507. 

alcohol, 505. 
Rutile, Ti0 2 , 385. 
Rye flour, 490. 

S, sulphur, 187. 
Saccharide, 494. 
Saccharine matters, 490. 
Safety-lamp, behaviour in mines, 98. 
Davy's, 97. 

precautions in using, 98. 
Stephenson's, 96. 
Safflower, 591. 
Saffron, 591. 
Sago, 480. 
Salad oil, 570. 
Sal-alembroth, 368. 
Sal-ammoniac, NH 4 C1, 120. 

action on metallic oxides, 270. 

composition by volume,270. 

vapour-density of, 270. 
Sal gem, 261. 
Salicine, 471. 

derivatives, 471. 
Salicyle, C 7 H 5 2 , 472. 
hydride, 472. 
Salicylic acid, HC 7 H 5 3 , 472. 
Saligenine, 472. 
Saline waters, 49. 
Saliretine, 472. 
Saliva, 621. 
Sal polychrest, 212. 
Sal-prunelle, 412. 
Salt-cake, 263. 



Salt as manure, 616. 
common, 261. 
definition, 26. 
etymology, 251. 
extraction, 261. 
fused, 115. 

-gardens of Marseilles, 262. 
-glazing, 406. 
of lemons, 576. 
of sorrel, 576. 
of tartar, 258. 
preservative effect, 626. 
table-, 262. 

unitary definition, 253. 
useful applications, 262. 
Salting of meat, 608. 
Saltpetre, KN0 3 , 409. 

as manure, 616. 
cubical, NaN0 3 , 409. 
-flour, 411. 
impurities, 411. 

prepared from nitrate of soda, 410. 
properties, 412. 
refining, 411. 
tests of purity, 412. 
Salt-radical, definition, 26. 
Salt-radicals, 186. 
Salts, acid, 252, 254. 

atomic unitary formula?, 253. 

basic, 252, 254. 

binary theory, 253. 

constitution of, 251. 

definition, 253. 

double, constitution, 254. 

haloid, 186, 251. 

mutual decomposition of, 410. 

neutral, 252. 

normal, 252. 

ratios of, 253. 
oxyacid, 251. 

water-type theory of, 255. 
Sal volatile, 269. 
Sand, 109. 
Sandarach, 467. 
Sandstone, 407. 

Craigleith, 407. 
Sap of plants, 617. 
Saponification by steam, 565. 

sulphuric acid, 564. 
theory of, 562. 
Saponine, 473. 
Sapphire, 287. 
Sarcosine, C 3 H 7 N0 2 , 606. 
Saturated solution, 39. 
Savin, essential oil of, 465. 
Saxon sulphuric acid, 202. 
Saxony blue, 595. 
Sb, antimony, 373. 
SbCl 3 , terchloride of antimony, 376. 
SbCl„ penta chloride of antimoiry, 377. 
Sbo0 3 , antimonic oxide, 375. 
Sb 2 5 , antimonic acid, 375. 
Sb. 2 S 3 , tersulphide of antimony, 377. 
Scammony, 475. 
Scarlet dyes, 596. 
Scheele's green, 2CuO.H 2 O.As 2 3l 244. 

prussic acid, 434. 
Scheelite, CaO.W0 3 , 386. 
Schlippe's salt, 378. 
Scotch pebbles, 109. 
Scott's cement, 409. 
Scrubber, 445. 



INDEX. 



659 



Se, selenium, 220. 
Seal-oil, 572. 
Sea-water, 49. 

extraction of silt from, 261. 
Sea-weed, 495. 
Sebacic acid, 571. 
Secretion, 623. 
Sedative salt, 116. 
Seeds, composition, 617. 
germination, 482. 
Sefstrom's furnace, 320. 
Sel d'or, 401. 
Selenic acid, Se0 3 , 221. 
Selenides, 221. 
Selenietted hydrogen, 221. 
Selenious acid, Se0. 2 , 221. 
Selenite, 278. 
Selenium, Se, 220. 

chlorides, 221. 
sulphides, 221. 
Seltzer water, 49. 
Separating funnel, 93. 
Sericine, 609. 
Serpentine, 281. 
Serum, 605. 
Shaft, downcast, 75. 

upcast, 75. 
Shamoying, 582. 
Shear-steel, 316. 

Sheep-dipping compositions, 244. 
Shell-lac, 467. 
Sherry, 504. 
Shot, 353. 
Si, silicon, 109. 
Sicilian sulphur, 187. 
Siemens' induction-tube, 52. 

regenerative furnace, 429. 
Sienna, 285. 

SiF 4 , fluoride of silicon, 184. 
Signal-light composition, 248. 
Silica, Si0 2 , 109. 

amorphous, 111. 
crystalline, 111. 

dissolved by hydrofluoric acid, 183. 
gelatinous, preparation, 185. 
in plants, 110. 
in waters, 110. 
Silicate of alumina and soda, 288. 

soda, 110. 
Silicated soap, 563. 
Silicates, 112. 

normal ratio of, 253. 
Silicic acid, Si0 2 , 109. 

hydrated, 111. 
solution of, 111. 
ether, 515. 
Silicide of magnesium, 115. 
Silicium, 113. 

ethyle, 527. 
methyle, 527. 
Silicofiuoric acid, 185. 
Silicon, Si, 109. 

action of hydrochloric acid on, 170. 

amorphous, 114. 

and nitrogen, 114. 

atomic weight, 115. 

bisulphide, 219. 

chloride, SiCl 4 , 170. 

diamond, 114. 

fluoride, SiF 4 , 184. 

importance in mineralogy, 
184. 



Silicon, fluoride, preparation, 184. 
fused, 114. 
graphitoid, 114. 
hydride, 114. 
resembles carbon, 114. 
Silicone, 115. 
Silk, 609. 
Silver, Ag, 359. 

action of hydrochloric acid on, 156. 

hydrosulphuric acid on, 196. 
amalgam, 366. 
arsenite, 243. 
basic periodate, 178. 
bromide, AgBr, 363. 
chloride, AgCl, 363. 

action of light on, 214. 
reduction of, 363. 
cleaned, 196. 
coin, 360. 
crucibles, 362. 
detected in lead, 352. 
extracted from its ores, 214. 
extraction by amalgamation, 359. 
from copper-ores, 359. 
lead, 351. 
frosted, 360. 

fulminate, Ag 2 C 2 N 2 2 , 441. 
fusing-point, 361. 
fulminating, 362. 
glance, Ag 2 S, 364. 
hyposulphite, 213. 
in lead, 349. 
iodide, 178. 
metaphosphate, 232. 
native, 359. 
nitrate, AgN0 3 , 362. 

preparation from standard 
silver, 362. 
nitride, 362. 
ore, red, 364. 
oxalate, 576. 
oxide, Ag 2 0, 362. 
oxides, 362. 
oxidised, 360. 
periodate, 178. 
plate, 360. 
properties, 361. 
pure", preparation, 361. 
pyrophosphate, 232. 
recovered from photographic baths, 

363. 
refining, 360. 

separated from copper, 362. 
solder, 360. 
stains removed, 362. 
standard, 360. 
subchloride, 363. 
sulphide, Ag. 2 S, 364. 
native, 359. 
tarnished, 196. 
tree, 366. 
triphosphate, 233. 
Silvering brass or copper, 361. 
dry, 361. 
glass, 361. 
Simple solution, 39. 
Si0. 2 , silicic acid, 109. 
Siphon eudiometer, 34. 
Size, 609. 

Slag, blast-furnace, composition, 304. 
iron in, 307. 
iron-refinery, 308. 



660 



INDEX. 



Slag, lead-furnace, 348. 

metal (copper), 336. 

ore-furnace, 335. 

puddling-furnace, 311. 

refinery (copper), 337. 

roaster (copper), 336. 
Slaked lime, CaO.H 2 0, 278. 
Slaking of lime, 42. 
Slate, 285. 
Slow portfire, 412. 
Smalt, 327. 
Smelling-salts, 269. 
Smoke, cause of, 67. 

consumption, 68. 
prevention, 68. 
Smokeless gas-burners, 103. 
Sn, tin, 378. 

SnCl 2 . protochloride of tin, 384. 
SnCl 4 , bicliloride of tin, 384. 
SnO, protoxide of tin, 383. 
Sn0 2 , binoxide of tin, 383. 
Snow, 51. 

SnS, protosulphide of tin, 384. 
SnS 2 , bisulphide of tin, 385. 
Snuff, 590. 

50 2 , sulphurous acid, 199. 

50 3 , sulphuric acid, 202. 
Soap, 561. 

arsenical, 244. 
Castile, 563. 
glycerine, 563. 
mottled, 563. 
-nut, 473. 
palm-oil, 562. 
rosin in, 563. 
silicated, 563. 
transparent, 563. 
-wort, 473. 
yellow, 563. 
Soaps decomposed by acids, 563. 
Soda, Na 2 0, 265. 

acid pyrophosphate, 233. 

action on hard waters. 48. 

aluminate, 288. 

arseniates, 245. 

arsenite, 244. 

ash, 264. 

manufacture, 263. 

basic periodate, 178. 

biborate, 266. 

bicarbonate, 265. 

bimetantimoniate, 375. 

bisulphate, 210. 

bitungstate, 387. 

carbonate, Na 2 O.C0 2 , 263. 

manufacture from common 

salt, 263. 
medicinal, 265. 

caustic, NaHO, 265. 

chloride, 161. 

common phosphate, 2Na 2 O.H 2 O.P 2 5 , 
233. 

crystals, 264. 

hydrate, 265. 

hypochlorite, 161. 

hypophosphite, 235. 

hyposulphite, Na 2 S 2 3 , 213. 

use in photography, 214. 

in blood, 607. 

-lime, 127. 

-lye, 265, 562. 

manganate, 325. 



Soda, manufacture of, history, 263. 

influence on useful 
arts, 264. 
metaphosphate, 234. 
nitrate, 268, 409. 

conversion into nitrate of pot- 
ash, 410. 
solubility, 410. 
obtained from kryolite, 266. 
oleate, 562. 
palmitate, 563. 

phosphate, 2Na 2 O.H 2 O.P 2 5 , 268. 
phosphite, 234. 
, platinate, 391. 
pyrophosphate, 233. 
silicate, 110, 267. 
stannate, Na 2 O.Sn0 2 , 383. 
stearate, 562. 
subphosphate, 233. 
sulphate, Na 2 O.S0 3 , 268. 

extracted from sea-water, 
262. 
sulphite, 201. 
sulphoxy-phosphate, 238. 
test for, 375. 
tetrathionate, 216. 
tungstate, Na 2 O.W0 3 , 380, 386. 
urate, 612. 
washing-, 264. 
waste, 213, 
-water, 76. 

powders, 77- 
Sodacetic ether, 559. 
Sodamide, NH 2 Na, 542. 
Sodium, Na, 261. 

action on water, 11. 
-alcohol, 519. 
-amalgam, 126. 
and oxygen, 25. 
aurochloride, 401. 
blowpipe test for, 266. 
chloride, 261. 

commercial importance, 

142. 
solubility, 410. 
equivalent weight, 11. 
-ethyle, 525. 
extraction, 266. 
fluoride, 183. 
-glycol, 551. 

line in the spectrum, 273. 
nitroprusside, 439. 
pentasulphide, 215. 
platinochloride, 392. 
silicofluoride, 115. 
sulphantimoniate, 197. 
sulpharseniate, 197. 
sulphostannate, 197. 
Soffioni, 116. 

artificial, 117. 
Softening waters, 47. 
Soft soap, 563. 
water, 44. 
Soils, formation, 77, 615. 
impoverished, 615. 
iron in, 321. 
Solanine, 529. 
Solder, 353. 

brazier's, 341. 
coarse, 381. 
fine, 381. 
silversmith's, 360. 



INDEX. 



661 



Soldering, use of sal-ammoniac in, 270. 
Soluble glass, 267. 
Solution, 39. 
Soot, 67. 

as manure, 616 
Sorbic acid, 580. 
Sorrel, salt of, 576. 
Soup, 607. 
Sparkling wines, 77. 
Sparteine, 529. 

Spathic iron ore, FeO.C0 2 , 300. 
Specific gravity of gases defined, 14, 21. 

influence of tempera- 
ture on, 193. 
liquids, defined, 51. 

determined, 122. 
solids, defined, 51. 
Specific beat defined, 421, 
of atoms, 9. 
of magnesium, 284. 
relation to atomic weights, 9. 
Specific beats of potassium, sodium, and 

lithium, 283. 
Spectroscope, 273. 
Spectrum analysis, 272. 

use of bisulphide of car- 
bon in, 217. 
Specular iron ore, Fe 2 3 , 300. 
Speculum metal, 340, 382. 
Speiss, 327. 
Spelter, 295. 
Spermaceti, 573. 
Sperm oil, 573. 
Spheroidal state, 200. 
Spices, preservative effect of, 626. 
Spiegel-eisen, 318. 
Sjpinelle, MgO.Al 2 3 , 287, 321. 
Spirit, methylated, 468. 
of salt, 144. 
of wine, 509. 
Spirits, 504. 

of turpentine, 464. 
Spirting avoided, 112. 
Sponge, 609. 

ashes of, 175. 
Spongy platinum, 390. 
Spontaneous combustion of phosphorus, 23. 
Springs, petrifying, 46. 
Spring water, 43, 76. 
Sprouting of silver, 352. 
Sr, strontium, 276. 
SrO, strontia, 276. 
SrO.C0 2 , carbonate of strontia, 276. 
SrO.N 2 5 , nitrate of strontia, 276. 
SrO.S0 3 , sulphate of strontia, 276. 
Stains of fruit removed, 200. 
Stalactites, 46. 
Stalagmites, 46. 
Stannates, 383. 
Stannic acid, Sn0 2 , 383. 

dialysed, 383. 
hydratcd, 383. 
chloride, SnCl 4 , 384. 
oxide, Sn0 2 , 383. 
sulphide, SnS 2 , 385. 
Stannous chloride, SnCl 2 , 384. 
oxide, SnO, 383. 
sulphide, SuS, 384. 
Star antimony, 373. 
Starch, C 6 H l0 O 5 , 478. 

action of water on. 480. 
a glueoside, 482. 



Starcb, and iodine, 177. 
blue, 291. 
commercial, 479. 
extraction from potatoes, 478. 
rice, 479. 
wheat, 479. 
from different plants, distinguished, 

480. 
in food, 480. 
iodised, 481. 
paste, preparation, 53. 
Stassfiirthite, 260, 410. 
Staurotide or staurolite, artificially formed, 

184. 
Steam, composition by volume, 35. 
decomposed by carbon, 86. 

chlorine, 149. 
electric sparks, 7. 
heat, 7. 
latent heat of, 427. 
specific gravity calculated, 36. 
Stearic acid, HC 18 H 35 2 , 507, 563. 
Stearic glucose, 568." 
Stearine, C 57 H 110 O 6 , 562. 
candles, 564. 
synthesis of, 565. 
Steatite, 279. 
Steel, 314. 

annealing, 316. 
Bessemer, 317. 
blistered, 315. 
cast, 316. 

distinguished from iron, 317. 
German, 318. 
hardening, 316. 
Krupp's, 318. 
made with coal-gas, 317. 
manufacture, 314. 
mild, 318. 
natural, 318. 
nitrogen in, 317. 
puddled, 318. 
shear, 316. 
tempering, 316. 
tilted, 315. 
titanium in, 317. 
Stereochromy, 267. 
Sterro-metal, 341. 
Stibethyle, Sb(C 2 H 5 ) 3 , 526. 
Stibiotriethyle, 526, 539. 
Stibio-trimethyle, 526. 
Still 49. 

Stockholm tar, 463. 
Stone, artificial, 267. 
-coal, 68. 
decayed, 408. 
test of durability, 408. 
-ware, 406. 
Storax, 466. 

Stout, composition, 486. 
Straits tin, 380. 
Stream-tin ore, 378. 
Strontia, carbonate, 276. 

nitrate, SrO.N 2 5 , 276. 
sulphate, 276. 
Strontianite, SrO.C0 2 , 276. 
Strontium, Sr, 276. 

action on water, 11. 

diatomic, 281. 

equivalent and atomic weights, 

284. 
properties, 276. 



662 



INDEX. 



Strontium, sulphide, 276. 
Struvite, 281. 

Strychnine, C 21 H ?2 N 2 2 , 589. 
constitution, 535. 
extraction, 589. 
identified, 589. 
properties of, 589. 
Stucco, 279. 
Styracine, 466. 
Styrole, 466. 
Suberic acid, 571. 
Sublimate, corrosive, 368. 
Sublimation, 120, 468. 
Sublimed sulphur, 415. 
Substitution, 11. 

of chlorine for hydrogen, 150. 
Substitutive formulae, 83. 
Succinic acid, H 2 C 4 H 4 4 , 468, 571. 

conversion into tartaric, 578. 
formed from tartaric, 578. 
Succussion, 208. 
Suet, 573. 

Sugar, action of oil of vitriol on, 208. 
adulteration, 490. 
-candy, 494. 

-cane, composition, 492. 
extraction, 492. 
from beet-root, 493. 
linen, &c, 490. 
-lime, 494. 
loaf, 493. 
maple, 493. 
of flesh, 607. 
of fruits, C 6 H 12 6 , 491. 
of gelatine, 609. 
of manna, 495. 
of milk, C 12 H 24 O l2 , 601. 
preservative effect of, 626. 
raw, 492. 
-refining, 65, 492. 
starch-, 490. 
uncrystallisable, 491. 
with chloride of sodium, 494. 
with oxide of lead, 494. 
Sugars, 490. 

chemical properties, 494. 
optical properties, 494. 
Sulphamylic acid, 517. 
Sulphantimoniates, 378. 
Sulphantimonites, 378. 
Sulpharsenic acid, 249. 
Sulpharsenious acid, 249. 
Sulphate of soda and lime, 268. 

crystallisation of, 40. 
composition, 40. 
Sulphates, 211. 

acid, 211. 

action of heat on, 212. 
additive formulas of, 212. 
double, 212. 
in common use, 212. 
native, 187. 
normal, 252. 

reduced to sulphides, 213. 
substitutive formulas of, 212. 
Sulphethylic acid, C 2 H 5 HS0 4 , 516. 
Sulphides, 197. 

action of air on, 198. 
native, 187. 

precipitated by hyposulphites, 
214. 
Sulphiudigotic acid, 595. 



Sulphindylic acid, 595. 
Sulphites, 201. 

normal ratio of, 253. 
Sulphobenzolic acid, 463. 
Sulphocarbonates, 218. 
Sulphocarbonic acid, 218. 
Sulphocyanide of ammonium, preparation, 

218. 
Sulphocyanogen, CyS, 437. 
Sulphogly eerie acid, 564. 
Sulpholeic acid, 565. 
Sulphopalmitic acid, 565. 
Sulphophosphotriamide, 239. 
Sulphosaccharic acid, 494. 
Sulphostearic acid, 565. 
Sulphovinic acid, C 2 H 5 HS0 4 , 516. 
Sulphoxyphosphoric acid, 238. 
Sulphur, S, 187. 

-acids, 197. 

action of alkalies on, 193. 
lime on, 198. 

allotropic states of, 192. 

amorphous or insoluble, 191. 

and oxygen, 23. 

bases, 197. 

chemical relations, 193. 

chloride, SC1 2 , 220. 

combining volume, 194. 

dichloride, S 2 C1 2 , 220. 

dimorphous, 192. 

distilled, 189. 

ductile, 191. 

electro-negative, 191. 

electro-positive, 191. 

examination of, 415. 

extraction, 188. 

from copper-pyrites, 

190. 
from iron pyrites, 189. 
from soda-waste, 264. 

flowers of, 189. 

for gunpowder, 414. 

function in gimpowder, 415. 

group of elements, 222. 

home sources of, 189. 

iodide, SI 2 , 220. 

milk of, 190. 

occurrence in nature, 187. 

octahedral, 192. 

of coal mines, 98. 

ores, 187. 

oxides, 199. 

oxidised and dissolved, 193. 
'by nitric acid, 132. 

plastic, 191. 

prismatic, 192. 

properties, 190. 

refining, 188. 

roll, 189. 

rough, 188. 

-salts, 197. 

subiodide, S 2 I 2 , 220. 

sublimed, 189. 

test for, 439. 

uses, 190. 

vapour density, 194. 
Sulphureous waters, 49. 
Sulphuretted hydrogen, H 2 S, 194. 
Sulphuric acid, H 2 S0 4 , 202. 

action on bromides, 174. 
"copper, 199. 
fats, 564. 



INDEX. 



66; 



Sulphuric acid, action on fluor-spar, 181. 
lead, 207. 
metallic oxides, 

211. 
metals, 209. 
organic matters, 

208. 
silver, 210. 
anhydrous, 210. 

preparation, 202. 
attraction for water, 209. 
caution in diluting, 209. 
combinations with water, 

210. 
composition, 211. 
concentrated, 208. 
concentration, 208. 
decomposition bv heat, 209. 
diluted, turbidity of, 209. 
distiUation of, 208. 
formation, 202. 
from the chambers, 207. 
fuming, 202. 
glacial, 210. 

hydrated, H 2 O.S0 3 , 202. 
manufacture, 205. 

chemical prin- 
ciples, 204. 
history of, 202. 
illustrated, 

204. 
summary, 208. 
Nordhausen, 202. 
polymerising by, 447. 
reduced by hydriodic acid, 

179. 
use in gas-analysis, 210. 
vapour-density of, 211. 
anhydride, 210. 

decomposed by heat, 
210. 
ether, 510, 516. 
Sulphuring casks, 201. 
Sulphurous acid, S0 2 , 199. 

a reducing agent, 201. 
action on hydrosulphuric 
acid, 216. 

nitric acid, 204. 
nitric peroxide, 

204. 
zinc, 215. 
hydrated, 202. 
liquefaction, 199. 
properties, 199. 
reduced by phosphorous 

acid, 234. 
separated from other gases, 

355. 
solubility in water, 200. 
anhydride, 202. 
Sulphuryle, 201. 
Sumach, 582. 

Superphosphate of lime, 224. 
Supersaturated solution, 40. 
Swedish iron ore, 300. 
Sweet oil, 570. 
Sweet spirits of nitre, 515. 
Syenite, 290. 
Sylvic acid, 465. 
Symbols, 2. 
Sympathetic ink, 41. 
Synaptase, 469. 



Synthesis of acetic acid, 525, 556. 

acids of the acetic series, 559. 

butyric acid, 559. 

formic acid, 558. 

guanidine, 537. 

hippuric acid, 613. 

hydrocyanic acid, 91. 

leucic acid, 553. 

neutral fats, 565. 

organic substances, 89, 430. 

propylic acid, 525. 

prussic acid, 91. 

taurine, 622. 

urea, 610. 

volatile fatty acids, 559. 

water, 31. 

by weight, 36. 

T, TARTAKIC ACID, 576. 

TagaliU, 344. 

Talc, 279. 

Tallow, 562, 573. 

Tank-waste, 213. 

Tannic acid, 581. 

Tannin, 581. 

Tanning, 581. 

Tantalic acid, 388. 

Tantalite, 388. 

Tantalum, Ta, 388. 

Tap-cinder, composition, 311. 

Tapioca, 481. 

Tar-charcoal, 414. 

Tar, coal, 445. 

wood, 460. 
Tarragon, essential oil of, 471. 
Tartar, 576. 

salt of, 258. 
-emetic, 577. 
Tartaric acid, H 2 C4H 4 6 , 576. 

artificial formation, 578. 
conversion into malic acid, 

578. 
conversion into succinic acid, 

578. 
formed from succinic acid, 
578. 
anhydride, 577. 
Tartrate'of potash and soda, 578. 
Taurine, C 2 H 7 N0 3 S, 622. 

artificial formation, 622. 
Taurocholic acid, 622. 
Tawing, 582. 
Te, tellurium, 221. 
Tea, composition, 587. 
Telluretted hydrogen, 222. 
Telluric acid, Te0 3 , 222. 
Telluride of bismuth, 222. 
Telluride of potassium, 222. 
Tellurium, Te, 221, 

characterised, 222. 
foliated, 222. 
graphic, 222. 
sulphides, 222. 
Tellurous acid, Te0 2 , 222. 
Temper spoilt, 317. 
Tempering, colours in, 317. 
Tenacity of copper, 339. 

iron, 339. 
Tendons, 608. 
Tennantite, 240. 
Terebene, 464. 
Terebilene. 464. 



664 



INDEX. 



Terequivalent elements, 158. 
Terne-plate, 381. 
Terpinole, 465. 
Terstearine, 565. 
Test tube, 30. 
Tetrad elements, 158. 
Tetramethylium, hydrate, 533. 
Tetramines, 538. 
Tetramylium, hydrate, 533. 
Tetrathionic acid, 215. 
Tetratomic elements, 158. 
Tetrethylarsonium, hydrate, 539. 
Tetrethylium, hydrate, N(C 2 H 5 ) 4 HO, 532. 

iodide, 532. 
Tetrethylphosphonium, hydrate, 539. 
Tetrethylstibonium, hydrate, 539. 
Tetrethyl-urea, 611. 
Thallium, Tl, 358. 

alcohol, 519. 

extracted from flue-dust, 358. 
for green fire, 358. 
salts, 358. 
Theine, C 8 H 10 N 4 O 2 , 587. 
Thenar elite, 268. 
Theobromine, C 7 H 8 N 4 2 , 588. 

converted into caffeine, 589. 
Theory, atomic, 8. 
Thermometers for very low temperatures. 

217. 
Thionyle, 201. 
Thiosinnamine, 530. 
Thorina, 291. 
Thorinum, Th, 291. 
Thorite, 291. 

Thyme, essential oil of, 465. 
Tile copper, 337. 
Tiles, 407. 
Tin, Sn, 378. 

action of acids on, 382. 

nitric acid on, 133. 
on hydrosulphuric acid, 196. 
water, 12. 

alloys of, 381. 

amalgam, 366. 

bichloride, SnCl„ 384. 

binoxide, Sn0 2 , 383. 

bisulphide, SnS 2 , 385. 

boiling, 380. 

crystals, 384. 

dropped, 380. 

extraction in the laboratory, 380. 

foil, 380. 

grain, 380. 

identified, 380. 

impurities, 383. 

metallurgy of, 378. 

nitromuriate, SnCl 4 , 384. 
Tin-ore of Montebras, 388. 
Tin-ores, mechanical treatment of, 378. 

oxychloride, 384. 

plate, 380. 

properties of, 380. 

protochloride, SnCl 2 , 384. 

protosulphide, SnS, 384. 

protoxide, SnO, 383. 

pure, preparation, 383. 
pyrites, SnS, 385. 

refining by liquation, 379. 

salts, 384. 

sesquioxide, 384. 

stannate, 384. 

-stone, Sn0 2 , 378. 



Tin tree, 384. 
Tincal, 116. 

refining of, 266. 
Tinned iron, 380. 
Tinning brass, 381. 

copper, 381. 
Tin-white cobalt, CoAs 2 , 327. 
Titanic acid, Ti0 2 , 386. 

dialysed, 386. 

extracted from iron- sand, 385. 
hydrated, 385. 
properties, 386. 
Titanic iron, 300. 
Titanium, Ti, 385. 

bichloride, 386. 

bisulphide, 386. 

cyanonitride, 386. 

metallic, 386. 

nitride, 386. 

protoxide, 386. 

sesquichloride, 386. 

sesquioxide, 386. 
Tl, thallium, 358. 
Toast, 481, 489. 
Tobacco, 589. 
Tokay, 504. 
Tolu balsam, 466. 

essential oil, 465. 
Toluidine, 452, 455, 534. 
Toluole, C 7 H 8 , 445. 
Tolylene, 537. 

diamine, 537. 
Topaz, 183, 287. 
Touch-paper, 412. 
Touch-stone, 133. 
Translation, rate of, 16. 
Trap-rock, 290. 
Treacle, 491. 
Tree- wax of Japan, 574. 
Triacetine, 555. 
Triacid triamines, 537. 
Triad elements, 158. 
Triamines, 537. 
Triamylamine, 533. 
Triatomic elements, 158. 
Tribasic phosphates, 233. 

phosphoric acid, 233. 
Tribenzoyl-phosphide, 542. 
Tribenzylamine, 550. 
Triborethyle, B(C 2 H 5 ) 3 , 526. 
Tricetylamine, 533. 
Trichloracetic acid, HC 2 C1 3 2 , 555. 
Trichloraniline, 540. 
Trichlorhydrine, 450. 

of phenose, 450. 
Triethylamine, N(C 2 H 5 ) 3 , 532. 
Triethylareine, As(C 2 H 5 ) 3 , 525, 539. 
Triethylene-octethyl-tetrammonium, 

hydrate, 538. 
Triethylene-tetralcohol> 554. 
Triethylene-tetramine, 538. 
Tri-ethylene-triamine, N 3 H 3 (C 2 H 4 ) 3 , 537. 
Trietliylphosphine, P(C 2 H 5 ) 3 , 539. 
Triethylstibine, Sb(C 2 H 5 ) 3 , 539. 
Trimethylamine, 538. 
Trimethylarsine, 525. 
Trinitro-cellulose, 497. 
Trinitrocresylic acid, 457. 
Trinitrophenic acid, 456. 
Triphane, 271. 
Triple phosphate, 281. 
Tripotassamide, NK 3 , 542. 



INDEX. 



665 



Trithionic acid, 215. 
Tungsten, W, 386. 

binoxide, 387. 

blue oxide, 387. 

chlorides, 387. 

metallic, 387. 

separated from tin ores, 380 . 

steel, 387. 

sulphides, 387. 

test for, 387. 
Tungstic acid, W0 3 , 386. 

dialysecb 386. 
Turbith or turpeth mineral, 368. 
Turkey red, 592. 
Turmeric, 593. 

action of boracic acid on, 117. 
Turnbull's blue, Fe 3 Fdcy, 438. 
Turner's yellow, 357. 
Turpentine, C 10 H 16 , 464. 

action of nitric acid on, 34. 
hydrates, 464. 
hydrocarbons, 465. 
in chlorine, 150. 
Twrqicoise, 291. 
Tuyere pipes, 301. 
Type furniture allov, 349. 
Type-metal, 353, 382. 
Types, chemical, 157. 

U, ueic acid, 612. 

Urinate of ammonia as manure, 609. 

Ulmic acid, 619. 

Ultramarine, artificial, 290. 

green, 290. 
Umber, 285. 

Uniequivalent elements, 158. 
Unitary definitions, 253. 

formulae, 42. 
Upcast shaft, 75. 
Uranium, U, 298. 

oxides, 298. 
Urea, CH 4 N 2 0, 609. 
analysis of, 127. 
artificial formation, 610. 
chemical constitution, 610. 
extraction from urine, 609. 
isomeric with cyanate of ammonia, 610. 
nitrate, 610. 
Ureides, 611. 
Uric acid, H 2 C 5 H 2 N 4 2 , 612. 

action of nitric acid on, 612. 
bibasic, 612. 

extraction from boa-excrement, 
612. 

urine, 612. 
Urine, 609. 

as manure, 616. 
composition, 614. 
putrefaction of, 609. 

Vacuum-pans, 492. 

Valentinite, 375. 

Valerian, essential oil of, 465. 

Valerianic acid, HC 5 H 9 2 , 507, 560. 

Valerian root, 560. 

Valerine, 573. 

Valerolactic acid, 552. 

Valerone. 548. 

Valeryle,' 549. 

Vanadic acid, 388. 

Vanadium, V, 388. 

chlorides, 388. 



Vanadium ink, 388. 

metallic, 388. 
oxide, 388. 
sulphide, 388. 
Vapour- densities, influence of temperature 

on, 193. 
Vapour-densities of the olefmes, 509. 
Varnishes, 468. 
Vegetable parchment, 210. 
Vegetation, chemistry of, 614. 
Venetian red, 321. 
Venice turpentine, 464. 
Ventilation, illustrations of, 74. 

necessity for, 74. 
Veratrine, 529. 
Verdigris, 555. 
Verditer, 343. 
Vert de Guignet, 331. 
Vermilion, HgS, 371. 
Vesta matches, 166. 
Vinegar, composition, 488. 

French, 488. 

malt, 488. 

manufacture, 487. 

mother of, 488. 

sulphuric acid in, 488. 

white wine, 488. 
Vinic acids, 516. 
Vitelline, 606. 
Vitriol-chambers, 206. 

corrosive properties of, 208. 
Vivianite, 322. 
Volcanic ammonia, 266. 
Volcano, artificial, 193. 
Voltameter, 33. 

Volume of gas, calculation of, 15. 
Volumes, combining, 36. 

of compound gases, 36. 
Vulcanised caoutchouc, 476. 
Vulcanite, 476. 

W, TUNGSTEN, 386. 

Wad, 324. 

Walls, efforescence on, 268. 
Washing precipitates, 112. 
Wash-leather, 582. 

Watch-spring for burning in oxygen, 27. 
Water, H 2 Q, 4. 

action upon metals, 10. 

analysis, 4. 

chemical relations of, 39. 

crystallisation of, 51. 

decomposed by battery, 4. 
heat, 7. 

distilled, 49. 

electrolysis of, 4. 

from natural sources, 42. 

-gas, 85. 

hard, 44. 

of constitution, 41. 

of crystallisation, Aq., 41. 

oxygenated, 51. 

purification, 49. 

soft, 44. 

synthesis, 31. 
Waterproof cloth, 476. 

felt, 476. 
Waters, ammonia detected in, 370. 

mineral, 49. 
Water-type theory of acids and salts, 255. 
Watery vapour, 51. 
Wavellite, 291. 

2u 



666 



INDEX. 



Wax, bees', 573. 

bleaching, 574. 
Chinese, 573. 
Weld, 591. 
Welding, 313. 

Weldon's chlorine process, 145. 
Well-water, 43. 
Welsh coal, 68. 
Whale-oil, 572. 
Wheat, composition, 479. 

sprouted, 482. 
Wheaten flour, 488. 
Whey, 601. 
Whisky, 504. 
White gunpowder, 164. 

iron, 306. 

lead, 355. 

manufacture, 356. 
ore, PbO.OOg, 346. 
metal, Cu 2 S, 335. 
precipitate, NH. 2 HgCl, 369. 

fusible, 369. 
vitriol, 297. 
Willow-bark, bitter principle, 471. 
Windows, crystals on, 269. 
Wine, 503. 
Wines, dry, 503. 

fruity, 503. 

proportion of alcohol in, 504. 

red, 503. 

ropy, 487. 

white, 503. 
Winter-green oil, 462. 
Wire iron, 311. 
Witherite, BaO.C0 2 , 274. 
Wolfram, 378, 386. 
Wood, carbonisation of, 62. 

-charcoal, 61. 

combustion, 61. 

composition, 459. 

destructive distillation of, 62, 459. 

for gunpowder-charcoal, 413. 

-naphtha, CH 4 0, 461. 

preservation of, 620. 

-smoke, 626. 

-spirit, 461. 

-tar, 460. 
Woody fibre, 460. 
Wool, 609. 

Wool and cotton, separation, 609. 
Worm, 49. 
Wormwood, 467. 
Wort, 484. 
Wrought iron, 307. 

Xantheine, 591. 
Xanthine, 591. 
Xylidine, 455. 
Xyloidine, 502. 
Xylole, 445. 



Yeast, 484. 

dried, 486. 
Yellow, chrome, 330. 

dyes, 597. 

fire, composi on for, 266. 

flowers, 591.1 

ochre, 300. 

orpiment, 248. 

Paris, 357. 
Yttrium, Y, 291. 
Yttrotantalite, 388. 

Zaffre, 328. 
Zinc, Zn, 292. 

-acetimide, 543. 

action of air on, 292. 

hydrochloric acid on, 156. 
sulphuric acid on, 296. 
on water, 12. 

-alcohol, 524. 

-amalgam, 366. 

amalgamated, 366. 

-amide, 543. 

-amyle, 525. 

and oxygen, 25. 

arsenide, 246. 

arsenite, 243. 

boiling-point, 293. 

carbonate, 293. 

chloride, 297. 

dissolved by potash, 296. 

distilled, 293. 

equivalent and atomic weights, 13. 

ethyle, Zn(C 2 H 5 ) 2 , 523. 

extraction, 293. 

Belgian method, 295. 
English method, 294. 
Silesian method, 295. 

granulated, 13. 

hyposulphite, 215. 

•identified, 296. 

impurities in, 296. 

metallurgy of, 293. 

-methyle, 524. 

nitride, 543. 

ores, 293. 

oxide, ZnO, 296. 

in glass, 404. 

oximide, 543. 

phenylimide, 543. 

removal of lead from, 296. 

sulphate, ZnO.S0 3 , 297. 

action of heat on, 212. 

sulphide, 293. 

valerianate, 560. 

-white, 296. 
Zircon, 292. 
Zirconia, 292. 
Zirconium, Zr, 292. 
ZnS, sulphide of zinc, 293. 



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WORKS 



CHEMISTRY, MATERIA MEDICA 

PHARMACY, BOTANY, 

THE MICROSCOPE, 

AND 

OTHER BRANCHES OF SCIENCE 



INDEX 

Beasley's Pocket Formulary ... ... ... ... ... ix 

Do. Druggist's Receipt Book ... ... ... ... ix 

Do. Book of Prescriptions ... ... ... .. ... ix 

Bentley's Manual of Botany ... ... ... ... ... xi 

Bernays' Syllabus of Chemistry ... ... .. ... ... iv 

Bloxam's Chemistry ... ... .. . . ... ... in 

Do. Laboratory Teaching ... ... ... ... ... iii 

Bowman's Practical Chemistry ... ... ... ... ... iv 

Brooke's Natural Philosophy ... ... ... ... . . xv 

Brown's Analytical Tables ... ... ... ... ... iv 

Carpenter's Microscope and its Revelations ... ... ... ... xii 

Chauveau's Comparative Anatomy ... ... ... ... xiii 

Cooley's Cyclopaedia of Receipts ... ... ... ... ... vi 

Dunglison's Medical Lexicon .. ... ... ... ... xiv 

Fayrer's Poisonous Snakes of India ... ... ... ... xii 

Fownes' Manual of Chemistry ... ... ... ... ... iv 

Frazer and Green's Druggists' Price Book ... ... ... ... ix 

Fresenius' Chemical Analysis ... ... ... ... ... iv 

Galloway's First Step in Chemistry ... ... ... ... v 

Do. Seconddo. do. ... ... ... ... ... v 

Do. Qualitative Analysis ... ... ... ... ... v 

Do. Chemical Tables ... ... ... ... ... v 

Greene's Tables of Zoology ... ... ... ... ... xiii 

Griffiths' Chemistry of the Four Seasons ... ... .. ... v 

Hardwich's Photography, by Dawson ... ... ... ... xv 

Huxley's Anatomy of Vertebrates... ... .. ... .. xiii 

Do. Classification of Animals... ... ... ... ... xiii 

Kay- Shuttle worth's Modern Chemistry ... ... ... ... v 

Kohlrausch's Physical Measurements ... ... ... ... xi 

Lescher's Elements of Pharmacy ... ... .. ... ... x 

Martin's Microscopic Mounting ... ... ... ... ... xii 

Mayne's Medical Vocabulary ... ... ... ... ... xiv 

Microscopical Journal (Quarterly)... ... ... ... ... xii 

Nevins' Analysis of Pharmacopoeia ... ... .. .. ix 

Ord's Comparative Anatomy • ... ... ... ... ... xiv 

Pereira's Selecta e Prsescriptis ... ... ... ... ... ix 

Pharmaceutical Journal and Transactions ... ... ... . xi 

Phillips' Materia Medica ... ... ... ... ... vii 

Preserver's Pharmacopoeia ... ... ... .. ... xi 

Price's Photographic Manipulation ... ... ... ... xv 

Proctor's Practical Pharmacy ... ... ... .. ... x 

Rod well's Natural Philosophy ... ... ... ... ... xv 

Royle's Materia Medica... ... ... ... ... ... vii 

Shea's Animal Physiology ... ... ... ... ... xiv 

Smith's Pharmaceutical Guide ... ... ... ... ••• viii 

Southall's Materia Medica ... ... ... ... ••• via 

Squire's Companion to the Pharmacopoeia ... ... ... ••• viii 

viii 



Do. Hospital Pharmacopoeias 

Steggall's First Lines for Chemists ... ... viii 

Stowe's Toxicological Chart ... ... ... ... • •• . x 

Sutton's Volumetric Analysis ... ... ... ... ••• v 

Thorowgood's Materia Medica ... ... ... ... ••• vii 

Tuson's Veterinary Pharmacopoeia ... ... ... ••• xi 

Valentin's Inorganic Chemistry ... ... ... ... ••• vi 

Do. Qualitative Analysis ... ... ... •••' ••• vi 

Vestiges of Creation ... ... ... . . . . , ... xiv 

Wagner's Chemical Technology ... ... ... ••• ... vii 

Wahltuch's Dictionary of Materia Medica ... ... ... ... vi 

Whalley's Human Eye ... ... ... ... •■• xii 

Wilson's Zoology ... ... ... •■■ ... ••• xiv 

Wittstein's Pharmaceutical Chemistry, by Darby ... ... ... x 

Year Book of Pharmacy ... ... ••• ... •■• xi 

%* The Works advertised in this Catalogue may be obtained through any Bookseller 

in the United Kingdom, or direct from the Publishers, on Remittance being made. 



A LIST OF 



Messrs CHURCHILL'S WORKS, &c 



C. L. Bloxa?n 

CHEMISTRY, INORGANIC and ORGANIC: 

With Experiments. By Charles L. Bloxam, Professor of Chemistry in 
King's College, London ; Professor of Chemistry in the Department for 
Artillery Studies, Woolwich. Second Edition. With 295 Engravings on 
W T ood .... . . 8vo, 1 6s. 

%* It has been the author's endeavour to produce a Treatise on Chemistry sufficiently 
comprehensive for those studying the science as a branch of general education, and one 
which a student may peruse with advantage before commencing his chemical studies at 
one of the colleges or medical schools, where he will abandon it for the more advanced 
work placed in his hands by the professor. The special attention devoted to Metallurgy 
and some other branches of Applied Chemistry renders the work especially useful to those 
who are being educated for employment in manufacture. 



" Professor Bloxam has given us a most 
excellent and useful practical treatise. His 
666 pages are crowded with facts and expe- 
riments, nearly all well chosen, and many 
quite new, even to scientific men. . . It 



is astonishing how much information he often 
conveys in a few paragraphs. We might 
quote fifty instances of this. " — Chemical 
News. 



By the same Author 

LABORATORY TEACHING: Or, Progressive Exercises in 
Practical Chemistry, with Analytical Tables. Third Edition. With 89 
Engravings ..... Crown 8vo, 5 s. 6d. 

* ** This work is intended for use in the chemical laboratory by those who are com- 
mencing the study of practical chemistry. It does not presuppose any knowledge of 
chemistry on the part of the pupil, and does not enter into any theoretical speculations. 
It dispenses with the use of all costly apparatus and chemicals, and is divided into 
separate exercises or lessons, with examples for practice, to facilitate the instruction of large 
classes. The method of instruction here followed has been adopted by the author, 
after twenty-three years' experience as a teacher in the laboratory. . 



Messrs Churchill's Works 



"John E. Bow?nan and C. L. Bloxam 

PRACTICAL CHEMISTRY, Including Analysis. 
By John E. Bowman and C. L. Bloxam. Sixth Edition. With 98 
Engravings on Wood . . . Fcap. 8vo, 6s. 6d. 

* \* The intention of this work is to furnish to the beginner a text -book of the prac- 
tical minutice of the laboratory. The various processes employed in analysis, or which 
have been devised for the illustration of the principles of the science, are explained in lan- 
guage as simple as possible. This edition has been embellished with a large number of 
additional wood engravings from sketches made in the laboratory. 



Albert J. Bernays 

NOTES FOR STUDENTS IN CHEMISTRY: Being a 
Syllabus of Chemistry and Practical Chemistry. By Albert J. Bernays, 
Professor of Chemistry at St. Thomas's Hospital. Fifth Edition, Revised. 

[Fcap. 8vo, 3s. 6d. 
%* A new feature is an Appendix giving the doses of the chief chemical preparations 
of the "Materia Medica." 



' ( The new notation and nomenclature are 
now exclusively used. We notice additional 
notes in apparently every paragraph in the 



book, and a close revision of the whole. "- 
Scientific Opinion. 



J. Cainpbell Brown 

ANALYTICAL TABLES for STUDENTS of PRACTICAL 
CHEMISTRY. By J. Campbell Brown, D.Sc. Lond., F.C.S. 

[8vo, 2s. 6d. 



G. Fownes 

MANUAL OF ELEMENTARY CHEMISTRY, 

Theoretical and Practical, By G. Fownes, F.R.S. Edited by Henry Watts, 
B.A., F.R.S. Eleventh Edition. With Wood Engravings. Crown 8vo, 15s. 



Remigius Fre senilis 

QUALITATIVE ANALYSIS. By C. Remigius Fresenius. 

Edited by Arthur Vacher. Eighth Edition, with Coloured Plate of Spectra 

and Wood Engravings .... 8vo, 12s.. 6d. 

By the same Author 

QUANTITATIVE ANALYSIS. Edited by Arthur Vacher. 

Sixth Edition (reprinted from the Fourth), with Wood Engravings. 8vo, 18s. 



Messrs Churchill's Works 



Robert Galloway 

THE FIRST STEP IN CHEMISTRY : A New Method for 

Teaching the Elements of the Science. By Robert Galloway, Professor 

of Applied Chemistry in the Royal College of Science for Ireland. Fourth 

Edition, with Engravings . . . Fcap. 8vo, 6s. 6d. 

By the same Author 

THE SECOND STEP IN CHEMISTRY: or, the Student's 
Guide to the Higher Branches of the Science. With Engravings. 

[Fcap. 8vo, ios. 
Also 

A MANUAL OF QUALITATIVE ANALYSIS 

Fifth Edition, with Engravings . . Post 8vo, 8s. 6d.. 

Also 

CHEMICAL TABLES: On Five large Sheets, for School and 
Lecture Rooms. Second Edition . . The Set, 4s. 6d. 



"We can always give praise to Mr. Gal- 
loway's educational works. They are inva- 
riably written on a system and founded on 
experience, and the teaching is clear, and 
in general complete." — Chemical News. 



" Mr. Galloway has done much to simplify 
the study of chemistry by the instructive 
manner in which he places the principal 
details of the science before his readers." 
— British Medical Journal. 



T. Griffiths 

CHEMISTRY OF THE FOUR SEASONS : Spring, Summer, 
Autumn, Winter. By T. Griffiths. Second Edition, with Engravings. 

[Fcap. 8vo, 7s. 6d. 



U. J. Kay-Shuftleworth 

FIRST PRINCIPLES OF MODERN CHEMISTRY. 

By U. J. Kay-Shuttleworth, M.P. Second Edition. Crown 8vo, 4s. 6d. 

"We can recommend the book." — I "Deserving warmest commendation."— 
Athenaeum. \ Popular Science Rev. 

Francis Sutton 

HANDBOOK OF VOLUMETRIC ANALYSIS; 

or, the Quantitative Estimation of Chemical Substances by Measure applied 

to Liquids, Solids, and Gases. By Francis Sutton, F.C.S., Norwich. 

Third Edition. With Engravings . . 8vo. In the Press 

%* This work is adapted to the requirements of pure Chemical Research, Pathological 

Chemistry, Pharmacy, Metallurgy, Manufacturing Chemistry, Photography, etc., and for 

the Valuation of Substances used in Commerce, Agriculture, and the Arts. 

"Mr. Sutton has rendered an essential service by the compilation of his work." — 
Chemical News. 



vi Messrs Churchill's Works 



R. V. Tuson 

COOLEY'S CYCLOPAEDIA OF PRACTICAL 

RECEIPTS, PROCESSES, AND COLLATERAL INFORMATION 
IN THE ARTS, MANUFACTURES, PROFESSIONS, AND 
TRADES : Including Pharmacy and Domestic Economy and Hygiene. 
Designed as a Comprehensive Supplement to the Pharmacopoeias and 
General Book of Reference for the Manufacturer, Tradesman, Amateur, 
and Heads of Families. Fifth Edition, Revised and partly Rewritten by 
Professor Richard V. Tuson, F.C.S., assisted by several Scientific 
Contributors ..... 8vo, 28s. 



" A much improved edition. . . . 
Long recognised as a general book of re- 
ference." — Times. 

• - The book is of considerable value for 
household use, as well as professional pur- 
poses, for it contains a quantity of interest- 
ing information relating to the composition 



of articles in common use as food and 
medicine." — Pall Mall Gazette. 

1 ' Other of the article s, as on ' brewing, ' 
'bread,' etc., are specimens of what cyclo- 
paedic writing should be, being concise and 
thoroughly exhaustive of the practical por- 
tion of the subject." — Veterinarian. 



W. G. Valentin 

INTRODUCTION TO INORGANIC CHEMISTRY. By 

Wm. G. Valentin, F.C.S., Principal Demonstrator of Practical Che- 
mistry in the Royal School of Mines and Science Training Schools, 
South Kensington. With 82 Engravings .... 8vo, 6s. 6d. 

Also 
QUALITATIVE CHEMICAL ANALYSIS. With 19 
Engravings 8vo, 7s. 6d. 

Also 
TABLES FOR THE QUALITATIVE ANALYSIS OF 
SIMPLE AND COMPOUND SUBSTANCES, both in the Dry and Wet 
Way. On indestructible paper . . . 8vo, 2s. 6d. 



Adolfihe Wahltuch 

A DICTIONARY OF MATERIA MEDICA AND THERA- 
PEUTICS. By Adolphe Wahltuch, M.D. . . 8vo, 15s. 

* # * The purpose of this work is to give a tabular arrangement of all drugs specified in 
the British Pharmacopoeia of 1867. Every table is divided into six parts :— (i) The 
Name and Synonyms ; (2) Character and Properties or Composition ; (3) Physiological 
Effects and Therapeutics; (4) Form and Doses; (5) Preparations ; (6) Prescriptions. 
Other matter elucidatory of the Pharmacopoeia is added to the work. 

" A very handy book." — Lancet. 



Messrs Churchill's Works 



R. Wagner and W . Crookes 

HANDBOOK OF CHEMICAL TECHNOLOGY. By 

Rudolf Wagner, Ph.D., Professor of Chemical Technology at the 
University of Wurtzburg. Translated and Edited from the Eighth German 
Edition, with Extensive Additions, by William Crookes, F.R.S. 

[8vo, 25s. 

* # * The design of this work is to show the application of the science of chemistry to 
the various manufactures and industries. The subjects are treated of in eight divisions, 
as follows : — 1. Chemical Metallurgy, Alloys, and Preparations made and obtained from 
Metals. 2. Crude Materials and Products of Chemical Industry. 3. Glass, Ceramic 
Ware, Gypsum, Lime, Mortar. 4. Vegetable Fibres. 5. Animal Substances. 6. Dye- 
ing and Calico Printing. 7. Artificial Light. -8. Fuel and Heating Apparatus. 



"Full and exact in its information on 
almost every point." — Engineer. 

" This book will permanently take its 
place among our manuals." — Nature. 



" Mr. Crookes deserves praise, not only 
for the excellence of his translation, but 
also for the original matter he has added." 
— American Journal of Science and Arts. 



C. D. F. Phillips 

MATERIA MEDICA AND THERAPEUTICS : VEGE- 
TABLE KINGDOM. By Charles D. F. Phillips, M.D. . 8vo. 

[Just ready. 



J. Forbes Royle and F. W. Headland 

A MANUAL OF MATERIA MEDICA. By J. Forbes 
Royle, M.D., F.R.S., and F. W. Headland, M.D., F.L.S. Fifth Edition, 
with Engravings on Wood . . . ' . . Fcap 8vo, 12s. 6d. 

%* This edition has beexi remodelled throughout on the basis of the present edition of 
the British Pharmacopoeia. The medicines of the British Pharmacopoeia will be found 
arranged in natural order, the preparations described at length, and the formulae 
explained. Other medicines and preparations, mentioned only in the London Pharma- 
copoeia of 185 1, are separately described and included in brackets. All remedies of 
value, whether officinal or not, are noticed in their place in this Manual. 



' ' This Manual is, to our minds, unrivalled 
in any language for condensation, accuracy, 



and completeness of information." — British 
Medical Journal. 



J. C. Thorowgood 

THE STUDENTS GUIDE TO MATERIA MEDICA. 

Including the New Additions to the British Pharmacopoeia. By John C. 
Thorowgood, M.D. Lond., Lecturer on Materia Medica at the Middlesex 
Hospital . . . . . Fcap 8vo, 6s. 6d. 



viii Messrs Churchill's Works 

J. B. Smith 
PHARMACEUTICAL GUIDE TO THE FIRST AND 
SECOND EXAMINATIONS. By John Barker Smith. Second 

Edition Crown 8vo, 6s. 6d. 

first and sf.cond examinations 
Latin Grammar — Fractions — Metric System — Materia Medica — Botany 
— Pharmacy— Chkmistry — Prescriptions. 



W. Southall 

THE ORGANIC MATERIA MEDICA OF THE BRITISH 
PHARMACOPOEIA SYSTEMATICALLY ARRANGED : Together 
with Brief Notices of the Remedies contained in the Indian and United 
States Pharmacopoeias. By W. Southall, F.L.S. . Post 8vo, 2s. 6d. 



Peter Squire 
COMPANION TO THE BRITISH PHARMACOPOEIA. 

With Practical Hints on Prescribing ; including a Tabular Arrangement 
of Materia Medica for Students, and a Concise Account of the Principal 
Spas of Europe. By Peter Squire, Chemist in Ordinary to the Queen 
and the Prince of Wales ; late President of the Pharmaceutical Society. 
Ninth Edition 8vo, ios. 6d. 

By the same Author 
PHARMACOPCEIAS OF THE LONDON HOSPITALS. 
Third Edition. . . Fcap 8vo, 6s. 

%* Mr. Squire has collected all the Formulae used in twenty-two of the principal 
Hospitals of London, and arranged them in groups of mixtures, gargles, &c., &c. These 
Formulas were revised and approved by the medical staff of each of the Hospitals, and 
may therefore be taken as an excellent guide to the medical practitioner, both as to dose 
and best menstruum in prescribing. 



John Steggall 
FIRST LINES FOR CHEMISTS AND DRUGGISTS 

preparing for Examination at the Pharmaceutical Society. By John 
Steggall, M.D. Third Edition . . . . . i8mo, 3s. 6d. 



Notes on the British Pharmacopoeia, the 
Substances arranged alphabeticallv. 

Table of Preparations, containing Opium, 
Antimony, Mercury, and Arsenic. 

Classification of Plants. 



CONTENTS 

Thermometers. 
Specific Gravity. 
Weights and Measures. 
Questions on Pharmaceutical Chemistry 
and Materia Medica. 



Messrs Churchill's Works ix 



J. Birkbeck Nevins 

THE PRESCRIBER'S ANALYSIS OF THE BRITISH 
PHARMACOPCEIA. By J. Birkbeck Kevins, M.D. Lond., Lecturer on 
Materia Medica in the Liverpool Royal Infirmary Medical School. Third 
Edition, Revised and Enlarged .... Royal 32mo, 3s. 6d. 

Jonathan Pereira 
SELECTA E PR^ESCRIPTIS : Containing Lists of the Terms, 
Phrases, Contractions, and Abbreviaticns used in Prescriptions, with Ex- 
planatory Notes ; the Grammatical Construction of Prescriptions ; Rules 
for the Pronunciation of Pharmaceutical Terms ; a Prosodiacal Vocabulary 
of the Names of Drugs, &c. ; and a Series of Abbreviated Prescriptions 
illustrating the use of the preceding terms. To which is added a Key, con- 
taining the Prescriptions in an Unabbreviated Form, with a Literal Trans- 
lation for the Use of Medical and Pharmaceutical Students. By Jonathan 
Pereira, M.D., F.R.S. Sixteenth Edition .... 32mo, 5s. 

Henry Beasley 

THE POCKET FORMULARY AND SYNOPSIS 

OF THE BRITISH AND FOREIGN PHARMACOPCEIAS : Compris- 
ing Standard and approved Formulae for the Preparations and Compounds 
employed in Madical Practice. By Henry Beasley. Ninth Edition. 

[i8mo, 6s. 
By the same Author 

THE DRUGGIST'S GENERAL RECEIPT-BOOK: 

Comprising a Copious Veterinary Formulary and Table of Veterinary 
Materia Medica ; Patent and Proprietary Medicines, Druggists' Nostrums, 
&c. ; Perfumery, Skin Cosmetics, Hair Cosmetics, and Teeth Cosmetics ; 
Beverages, Dietetic Articles and Condiments ; Trade Chemicals, Mis- 
cellaneous Preparations and Compounds used in the Arts, &c. ; with useful 
Memoranda and Tables. Seventh Edition .... i8mo, 6s. 

Also 
THE BOOK OF PRESCRIPTIONS : Containing 3,000 Pre- 
scriptions collected from the Practice of the most eminent Physicians and 
Surgeons, English and Foreign. Fourth Edition . . . i8mo, 6s. 



"Mr. Beasley's 'Pocket Formulary,' 
* Druggist's Receipt-Book,' and ' Book of 
Prescriptions' form a compact library of 



reference admirably suited for the dispens- 
ing desk." — Chemist and Druggist. 



Frazer and Green 

THE DRUGGIST'S STOCK AND PRICE BOOK. 

Comprising the Drugs, Sundries, and Proprietary Articles in general use, 
with Ruled Columns for Stock-taking Purposes, and for recording the Cost 
and Retail Price of every Article kept in Stock. Arranged by Frazer 
and Green, Pharmaceutical Chemists to the Queen, Glasgow. 8vo, 3s. 6d. 



Messrs Churchill's Works 



F. H. Lescher 
AN INTRODUCTION to the ELEMENTS of PHARMACY. 
By F. Harwood Lescher. Fourth Edition . 8vo, 7s. 6d. 

Detec- 



Sec. I. 

II. 

III. 



IV. 
V. 



VI. 



Materia Medica : Characteristics of Drugs ; Geographical Sources , 

tion of Spurious Specimens. 
Botany : Sketch of Organs, with their Functions ; Groupings of the 

Characteristics ; Natural Orders. 
Chemistry : Outline of Physics ; Simple Primary Analysis ; Detection of 

Adulterations ; Poisons — Tests and Antidotes ; Organic and Inorganic 

Chemicals. 
Pharmacy : Pharmacopoeia ; Preparations ; Active Ingredients. 
Prescriptions : The Latin Language ; Examples, with Errors and Unusual 

Doses ; Tables of Doses. 
Practical Dispensing : Groupings of Strengths of Solutions ; Emulsions ; 

Pills, &c. ; Changes in Mixtures. 



B % S. Proctor 
LECTURES ON PRACTICAL PHARMACY. 

By Barnard S. Proctor, Lecturer on Pharmacy at the College of Medi- 
cine, Newcastle-on-Tyne. With 43 Wood Engravings 8vo, 12s. 

*** The object of the writer is to assist earnest Students by indicating the direction 
and manner in which the study of Pharmaceutical subjects should be pursued ; attention 
being principally directed to such points as are not included in the usual Manuals of 
Chemistry and Materia Medica. The object is divided into — 

Abstract Processes : Drying, Grinding, Solution, Diffusion, Filtration, etc. 
Official Processes. 

Extempore Processes : Dispensing Mixtures, Pills, Plasters, Ointments, etc. Read- 
ing difficult Autographs, illustrated with lithographic fac-similes. 
Official Testing. Notes on the Qualitative and Quantitative Systems of the Pharma- 
copoeia. 
Pharmacy of Special Drugs, being Studies of Cinchona, Opium, Aloes, and Iron. 

William Stowe 
A TOXICOLOGICAL CHART, Exhibiting at one view the 
Symptoms, Treatment, and Mode of Detecting the Various Poisons, 
Mineral, Vegetable, and Animal. To which are added concise Directions 
for the Treatment of Suspended Animation. By William Stowe, 
M.R.C.S.E. Thirteenth Edition .... Sheet, 2S. ; Roller, 5s. 



G. C. Wittstein 

PRACTICAL PHARMACEUTICAL CHEMISTRY: An 

Explanation of Chemical and Pharmaceutical Processes ; with the Methods 
of Testing the Purity of the Preparations, deduced from Original Experi- 
ments. By Dr. G. C. Wittstein. Translated from the Second German 

Edition by Stephen Darby i8mo, 6s. 

" It would be impossible too strongly to recommend this work to the beginner, for the 

completeness of its explanations, by following which he will become well grounded 

in practical chemistry. " — From the Introduction by Dr. Buchner. 



Messrs Churchill's Works xi 

THE PRESCRIBER'S PHARMACOPCEIA : The Medicines 
arranged in Classes according to their Action, with their Composition 
and Doses. By A Practising Physician. Fifth Edition. 

[Fcap i6mo, cloth, 2s. 6d.; roan, with flap and elastic band, 3s. 6d. 

THE PHARMACEUTICAL JOURNAL AND TRANSAC- 
TIONS. Published weekly Price 4d. 



THE YEAR-BOOK OF PHARMACY: Containing the 
Proceedings at the Yearly Meeting of the British Pharmaceutical Con- 
ference, and a Report on the Progress of Pharmacy, which includes notices 
of all Pharmaceutical Papers, new Processes, Preparations, and Formulas 
published throughout the world. Published annually. 

[8vo, 1870, '71, '72, 7s. 6d. each ; 1873, IQ s. 



R. V. Tuson 

A PHARMACOPCEIA, INCLUDING THE OUTLINES OF 

MATERIA MEDICA AND THERAPEUTICS, for the. Use of Prac- 
titioners and Students of Veterinary Medicine. By Richard V. TUSON, 
F.C.S., Professor of Chemistry and Materia Medica at the Royal 
Veterinary College. Second Edition 7s. 6d. 

" Not only practitioners and students of want in veterinary literature." — Chemist 
veterinary medicine, but chemists and and Druggist. 
druggists will find that this book supplies a 



Robert Bentley 

A MANUAL OF BOTANY: Including the Structure, Func- 
tions, Classifications, Properties, and uses of Plants. By Robert 
Bentley, F.L.S., Professor of Botany, King's College, and to the Pharma- 
ceutical Society. Third Edition, with 1,138 Wood Engravings. 

[Crown 8vo, 14s. 

"As the standard manual of botany its position is undisputed." — Chemist and 
Druggist. 

F. Kohlransch 
AN INTRODUCTION TO PHYSICAL MEASUREMENTS, 
With Appendices on Absolute Electrical Measurement, etc. By Dr. F. 
KOHLRAUSCH. Translated from the Second German Edition by T. H. 
Waller, B.A, B. Sc, and H. R. Procter, F.C.S. With Engravings. 

[8vo, 12s. 



Xll 



Messrs Churchill's Works 



THE MICROSCOPE 
W. B. Carpenter, M.D., 
Engravings 



W. B. Carpenter 

AND ITS REVELATIONS. By 

F.R.S. Fifth Edition, with more than 500 Wood 

Crown 8vo. Just ready. 



%* The author has aimed to combine within a moderate compass that information in 
regard to the use of his instrument and its appliances, which is most essential to the 
working microscopist, with such an account of the objects best fitted for his study as may 
qualify him to comprehend what he observes, and thus prepare him to benefit science, 
whilst expanding and refreshing his own mind. 



J. H. Martin 

A MANUAL OF MICROSCOPIC MOUNTING; with Notes 
the Collection and Examination of Objects. By John H. Martin, 
Microscopic Objects." With upwards of 100 Engravings. 

[8vo, 7s. 6d. 

*** The aim of this work is to supply the student with a concise manual of the prin- 
ciples of microscopic mounting, and to assist his progress in the manual dexterity, as far 
as illustrations and words render it possible, necessary in their application. 



on 
author of 



THE QUARTERLY JOURNAL OF MICROSCOPICAL 

SCIENCE. (Established in 1852.) Edited by Dr. J. F. Payne, Demon- 
strator of Morbid Anatomy, and Assist.-Physician at St. Thomas's Hospital ; 
Mr. E. Ray Lankester, Fellow of Exeter College, Oxford ; and W. T. 
Thiselton Dyer, Professor of Botany to the Royal Horticultural Society. 
[Annual Subscription, 16s. ; Single Numbers, 4s. 

%* The Memoirs are, when needful, illustrated by Lithographic Plates, many of which 
are Coloured. The Journal contains, in addition, Notes and Memoranda, Reviews of 
Books, Quarterly Chronicle, and Proceedings of Societies. 



J. Fayrer 

THE THANATOPHIDIA OF INDIA; being a Description 

of the Venomous Snakes of the Indian Peninsula. With an Account of 
the Influence of their Poison on Life, and a Series of Experiments. By 
J. Fayrer, M.D., C.S.I., Honorary Physician to the Queen ; late President 
of the Asiatic Society of Bengal. Second Edition, with 31 Plates (28 
Coloured) . Folio, 7/. 7s. 



IV. Whalley 

THE HUMAN EYE, WITH REMARKS ON THE EYES 

OF INFERIOR ANIMALS : A Popular Description. By W. Whalley, 
M.R.C.S. With 40 Engravings . . . Fcap 8vo, 3s. 



Messrs Churchill's Works 



A. Chauveau and G. Fleming 

CHAUVEAU'S COMPARATIVE ANATOMY OF THE 

DOMESTICATED ANIMALS. Translated from the Second French 
Edition, and Edited by GEORGE FLEMING, F.R.G.S., Veterinary Surgeon, 
Royal Engineers ; Author of " Travels on Horseback in Mantchu Tartary," 
" Horse-shoes and Horse-shoeing," " Animal Plagues," etc. With 450 
Engravings on Wood .... 8vo, ^1 us. 6d. 



" The want of a text-book on the Com- 
parative Anatomy of the Domesticated 
Animals has long been felt. The present 
work is the fruit of a desire to fill a void in 
medical literature which has always existed, " 
so far as the English language is concerned. 
The care and attention with which hippo- 
tomyhas been cultivated on the Continent 
are illustrated by every page in M. Chau- 
veau's work. ... If we compare the 
description, say of the arteries of the head 
and neck of the horse, as given in Chau- 
veau's work, with the elaborate description 
given in Quain or Ellis of the same arteries 
in man, we shall find that in minuteness of 
detail the anthropotomist has been very 
closely rivalled by the hippotomist. . . 
In taking leave of this book we may con- 
gratulate Mr. Fleming on the completion 
of so great and useful an undertaking. He 
has translated his author into excellent 
scientific English, and his contributions 
(which in the text are placed between 
brackets) are proof of the large amount of 
study and research he has given to make 



the book as complete as possible. He has 
not only produced a most valuable— and, 
in fact, the only — anatomical text-book for 
the veterinary student, but he has given us 
a work to be prized by every scientific 
man who wishes to become acquainted with 
the anatomy of the higher vertebrata." — 
Medical Times and Gazette, May 10, 1873. 
"This is a valuable work, well con- 
ceived and well executed by the authors, 
MM. Chauveau and Arloing, and well 
translated by Mr. Fleming. Altogether 
the work reminds us very much of Quam 
and Sharpey's, where the histological part 
in the latter intercalated with the syste- 
matic ; and this is giving it no slight praise. 
We have compared M. Chauveau's descrip- 
tion of the bones and other organs, where 
practicable, with those of O^en, Huxley, 
Flower, and other English writers, and find 
that they are in general very accurate and 
good. . . . The ihustrations are very 
numerous, and Mr. Fleming has introduced 
a large number that are not contained in 
the original work. " — Lancet, May 31, 1873. 



y. Reay Greene 

TABLES OF ZOOLOGY: indicating the Tribes, Sub-Orders, 

Orders, and Higher Groups of the Animal Kingdom, for Students, 

Lecturers, and others. By J. Reay Greene, M.D., Professor of Natural 

History in the Queen's University in Ireland. Three large sheets, 7s. 6d. 

the set; or, mounted on canvas, with roller and varnished . . 18s. 

%* These Tables have been carefully prepared in accordance with the present state of 

science, and with a view to remove the difficulties which arise from the various opinions 

held by different zoologists. 

T. H. Huxley 

A MANUAL OF THE ANATOMY OF VERTEBRATED 
ANIMALS. By Prof. Huxley, LL.D., F.R.S. With numerous Engrav- 
ings. [Fcap. 8vo, 12s. 

By the same Author 

INTRODUCTION to the CLASSIFICATION of ANIMALS. 
With Engravings 8vo, 6s. 



XIV 



Messrs Churchill's Works 



W. M. Ord 

NOTES ON COMPARATIVE ANATOMY: a Syllabus of 

a Course of Lectures delivered at St. Thomas's Hospital. By William 

Miller Ord, M.B. Lond., MR C.P., Assistant-Physician to the Hospital, 

and Lecturer in its Medical School Crown 8vo, 5s. 

" Compact, lucid, and well arranged. 
These Notes will, if well used, be valuable 
to learners, perhaps still more so to 
teachers. " — Nature. 



' ' We have gone through it carefully, and 
we are thoroughly satislied with the manner 
in which the author has discharged his task." 
— Pop. Science Review. 



Johit Shea 

A MANUAL OF ANIMAL PHYSIOLOGY. With Appendix 

of Examination Questions. By JOHN Shea, M.D., B.A. Lond. With 



numerous Engravings . . . 

VESTIGES of the NATURAL HISTORY 

With 100 Engravings on Wood. Eleventh Edition 



Fcap. 8vo, 5s. 6d. 

OF CREATION. 

Post 8vo, 7s. 6d. 



Andrew Wilson 

THE STUDENT'S GUIDE TO ZOOLOGY: 

A Manual of the Principles of Zoological Science. By Andrew Wilson, 
Author of i: Elements of Zoology," and Lecturer on Zoology, Edinburgh. 
With Engravings . . . . . . Fcap 8vo, 6s. 6d. 

/?. G. Mayne 

MEDICAL VOCABULARY : an Explanation of all Names, 

Synonyms, Terms, and Phrases used in Medicine and the Relative 

Branches of Medical Science, giving their correct Derivation, Meaning, 

Application, and Pronunciation. Intended specially as a Book of Reference 

for the Young Student. Third Edition . . . Fcap 8vo, 8s. 6d. 

" We have referred to this work hundreds Botanical, and Pharmaceutical Terms are 
of times, and have always obtained the in- to be found on almost every page." — 
formation we required . . . Chemical, Chemist and Druggist. 



R. Dunglison 
MEDICAL LEXICON: A DICTIONARY OF MEDICAL 

SCIENCE. Containing a Concise Explanation of the various Subjects 
and Terms of Anatomy, Physiology, Pathology, Hygiene, Therapeutics, 
Pharmacology, Pharmacy, Surgery, Obstetrics, Medical Jurisprudence, and 
Dentistry, Notices of Climate and of Mineral Waters, Formulae for Officinal, 
Empirical, and Dietetic Preparations ; with the Accentuation and Etymo- 
logy of the Terms, and the French and other Synonyms. By Robley 
Dunglison, M.D. New Edition, thoroughly Revised by Richard J. 
Dunglison, M.D. . . . Royal 8vo (1,130 pp.), 28s. 

* \* The object of the author from the outset has been to make the work an epitome 
of the existing condition of medical science. Starting with this view, the great demand 
which has existed for the work has enabled him, in repeated revisions, to augment its 
completeness and usefulness, until at length it has attained the position of a recognised 
and standard authority. 



Messrs Churchill's Works xv 



Lake Price 

A MANUAL OF PHOTOGRAPHIC MANIPULATION. 

By Lake Price. Second Edition, Revised and Enlarged, with numerous 

Engravings Crown 8vo, 6s. 6d. 

%* Amongst the Contents are the Practical Treatment of Portraits— Groups in the 
Studio— Landscapes — Groups in Open Air — Instantaneous Pictures — Animals — Architec- 
ture—Marine Subjects— Still Life— Copying of Pictures, Prints, Drawings, Manuscripts, 
Interiors — Stereoscopy in Microphotography, &c, and Notices of the last Inventions 
and Improvements in Lenses, Apparatus, &c. 



" In these days, when nearly every intel- 



ligent person can, after a few weeks, master - Price, in the volume before us, proves 



the manipulatory details of our art-science, 
attention to the artistic treatment of sub- 
jects is a matter for the serious considera- 
tion of the Photographer ; and to those who 

I 



desire to enter on this path, Mr. LAKE 



himself to be 'a guide, philosopher, and 
friend.' "—The British Journal of Photo- 
graphy . 



G. Dawson 

A MANUAL OF PHOTOGRAPHY. By George 

Dawson, M.A., Ph.D., Lecturer on Photography in King's College, London. 
Eighth Edition, with Engravings . . Fcap 8vo, 5s. 6d. 



" The new edition of this excellent 
manual, which is founded on and incorpo- 
rates as much of Hardwich's ' Photographic 
Chemistry ' as is valuable in the present 
further advanced stage of the art, retains 
its position as the best work on the subject 
for amateurs, as wel! as professionals. The 



many new methods and materials which 
are so frequently being introduced, make it 
essential that any book professing to keep 
up to the times must be frequently revised, 
and Dr. Dawson has in this work presented 
the subject in its most advanced position." 
— Nature, May 29, 1873. 



C. Brooke 
THE ELEMENTS OF NATURAL PHILOSOPHY. By 

Charles Brooke, M.B., M.A., F.R.S. Based on the Work of the late 
Dr. GOLDING Bird. Sixth Edition, with 700 Engravings on Wood. 

[Fcap 8vo, 12s. 6d. 

CONTENTS 

I, E'ementary Laws and Properties of Matter : Internal or Molecular Forces — 
2, Properties of Masses of Matter : External Forces — 3, Statics — 4, The Mechanical 
Powers, or Simple Machines — 5, Principles of Mechanism — 6, Dynamics — 7, Hydro- 
statics — 8, Hydrodynamics — 9, Pneumatics — 10, Acoustics — II, Magnetism; Diamag- 
netism— 12, Franklinic Electricity— 13, Voltaic Electricity — 14, Electro- Dynamics — 
15, Electro-Telegraphy — 16, Thermo-Electricity — 17, Organic Electricity — 18, Catop- 
trics and Dioptrics — 19, Chromatics — 20, Optical Instruments -21, Polarised Light — 
22, Chemical Action of Light : Photography — 23, Thermics — 24, Radiant Heat. 

G. P. Ro dive II 

NOTES ON NATURAL PHILOSOPHY. 

By G. F. RODWELL, F.R.A.S., Lecturer on Natural Philosophy in Guy's 
Hospital, Science Master in Marlborough College. With 48 Wood Engrav- 
ings ..... Crown 8vo, 5s. 



"As an introductory text-book for this 
Examination [the Preliminary Scientific 
(M.B.) of the University of London], it is 
quite the best one we have seen . . The 
Notes ' chiefly consist of lucid and con- 
cise definitions, and everywhere bristle with 



the derivations of scientific terms." — 
Nature. 

11 A well-arranged and carefully-written 
condensation of the leading facts and prin- 
ciples of the chief elements of Natural 
Philosophy." — Chemical Nws. 



The following Catalogues issued by Messrs Churchill 
will be forwarded post free on application : 

1. Messrs Churchill's General List of nearly 600 works on 

Medicine, Surgery, Midwifery, Materia Medica, Hygiene, 
Anatomy, Physiology, Chemistry, &c, &c, with a complete 
Index to their Titles for easy reference. N.B. This List 
includes those which follow. 

2. Selection from Messrs Church ill's General List, comprising 

all recent works published by them on the A rt and Science 
of Medicine. 

3. A Selected and Descriptive List of Messrs ChurcliilVs works 

on Chemistry, PJiarmacy, Botany, Photography, and other 
branches of Science. 

4. Messrs ChurcJiilVs Red- Letter List, giving the Titles of 

forthcoming New .Works and Nezv Editions. 

[Published every October.] 

5. The Medical Intelligencer, an Annual List of New Works 

arid Nezv Editions published by Messrs J. & A. Churchill, 
together with Particulars of the Periodicals issued from 
their House. 

[Published every January.] 

[Sent at the commencement of each year to every Medical Practitioner in 
the United Kingdom whose name and address can be ascertained. A 
large number are also forwarded to the United States of America, 
Continental Europe, India, and the Colonies.] 



Messrs CHURCHILL have a special arrangement with Messrs 
LINDSAY & BLAKISTON, of Philadelphia, in accordance with 
which that Firm acts as their Agents for the United States of America, 
either keeping in Stock most of Messrs Churchill's Books, or reprinting 
them on Terms advantageous to Authors. Many of the Works in this 
Catalogue may therefore be easily obtained in America. 



?£' '^i'Gsyoan &> Co., Printers, Great Windmill Street, Hay market. 



